By Meteorologist, Liz Walsh

The 2020 Hurricane Season is shaping up to be one of the most active hurricane seasons on record with 20 named storms so far as of Friday 18^th September 2020 at 9am Irish Time.

The average number of storms over the entire season which stretches from June 1 through to November 30 is 12, with 6 of those storms strengthening to hurricane, and 3 of the 12 strengthening to Major Hurricane Strength (classified as Category 3 or more on the Saffir- Simpson Hurricane Wind Scale [1]). Note that a tropical storm is a tropical cyclone that has maximum sustained surface winds ranging from 39-73 mph / 63-119 km/h / 34-63 knots). A hurricane is a tropical cyclone that has maximum sustained surface winds of 74 mph / 119 km/h/ 64 knots or greater.

On the 14^th September, the US National Hurricane Center issued advisories on five tropical cyclones over the Atlantic basin – tying with the record for the most number of tropical cyclones in that basin at one time, last set in September 1971.

Image above from National Hurricane Center on September 14^th 2020.

As predicted by the US National Oceanic and Atmospheric Administration [2], the 2020 season has seen an exceptionally high number of named storms, reaching the letter V (Vicky) as of Monday 14 September. Vicky is the earliest 20^th Atlantic named storm on record.  The old record was set by Vince on October 9, 2005. The season lasts until 30 November.

Only the name Wilfred remains, and there are currently two tropical disturbances that are candidates to claim that name over the next day or so. One disturbance located over the south-western Gulf of Mexico currently labelled as Tropical Depression Twenty-two, and another disturbance located a few hundred miles southwest of the Cabo Verde Islands off the coast of West Africa. So it is quite possible that both Wilfred and Alpha could be named by the National Hurricane Center by the end of this weekend.

The hurricane name lists include only 21 letters out of 26, because it is not easy to find 6 appropriate names (for the 6 rotating lists) starting with Q, U, X, Y and Z. In the interests of safety, names must be easily recognizable. In addition, they have to reflect a balance between French, Spanish and English names due to the geographical coverage of the storms throughout the Atlantic and Caribbean, and respect societal sensitivities.

The use of the Greek alphabet (Alpha, Beta, Gamma, Delta, Epsilon, Zeta, Eta, Theta, etc.) has only happened once before in 2005, when six names from the Greek Alphabet were used.

Image above from the World Meteorological Organisation

2005 was a record-breaking year with devastating hurricanes including Katrina, Rita and Wilma, whose names were all retired.

While 2020 is comparable to 2005 with regard to the number of storms, the strength or intensity of the storms so far this year has been less. By the 18^th September in 2005, there had been 4 storms that had become major Hurricanes (classified as Category 3 or more) in the Atlantic Basin (including Katrina) and advisories had begun on what would become the 5^th one, Rita.

In comparison, this year, 2020, there have been only 2 storms that have reached major hurricane status in the basin so far, Hurricane Laura, which reached Category 4 on the 26^th August and Hurricane Teddy which intensified to a Category 4 hurricane last night (Irish time) and is expected to approach Bermuda this weekend. There are still over two months left in the season so there is still time for additional storms to join Laura and Teddy on the list of Major Hurricanes for 2020.

Factors that have been cited by the National Oceanic and Atmospheric Administration to cause this “extremely active” hurricane season include

• warmer-than-average sea surface temperatures in the tropical Atlantic Ocean and Caribbean Sea
• reduced vertical wind shear (i.e. change in wind speed or direction with change in height)
• weaker tropical Atlantic trade winds (Trade winds are the prevailing easterly winds that flow in the Earth’s equatorial region)
• an enhanced West African Monsoon (Characterised by changes in surface wind field over Western Africa leading to summer rainfall (wet season) and winter drought (dry season)).

Climate Drivers

A main climate factor driving the above mentioned conditions is the ongoing warm phase of the Atlantic Multi-Decadal Oscillation, which reappeared in 1995 and has been favouring more active hurricane seasons since that time.

Another contributing climate factor this year is the possibility of La Niña developing in the months ahead. La Niña conditions are classified as cooler-than-average sea surface temperatures in the equatorial regions of the eastern Pacific Ocean. Downstream effects of La Niña can further weaken the wind shear over the Atlantic Basin, allowing storms to develop and intensify. Current key indicators are currently at or approaching La Niña thresholds [3].

Image above from NOAA Climate.gov

Hurricane Season and Climate Change

The general consensus among the scientific community at the moment is that the warmer waters we are likely to experience in a warmer world will lead to stronger storms. What is less agreed upon, though, is the number of storms. The general hypothesis is that we expect to see either a decrease in the overall frequency of hurricanes or for it to remain unchanged. This scenario is generally believed to be a by-product of increasing wind shear in the tropics. There is not a perfect consensus on this, however, with a smaller number of studies that simulate an increase in the number of storms. So in terms of number of storms, this is still an area of active research.

An increase in the frequency of very intense storms, however, is generally accepted as a consequence of climate change regardless of whether the number of storms increase/decrease or stay the same. The impacts of this trend are likely to be exacerbated by sea level rise and a growing population along coastlines.  There is also the possibility that where cyclones reach maximum intensity will extend further northwards or poleward due to warmer sea surface temperatures.

What can we expect over the next couple of weeks and months?

The large scale pattern looks to generally remain conducive for Atlantic hurricane formation and intensification, although not as conducive as during the past two weeks according to the latest forecasts from Colorado State University of Atlantic Hurricane Activity as of the 16^th September 2020. [4].

We have passed the peak of Atlantic Hurricane Season but there is still a way to go and as we head through the latter part of September and October. The delayed warming of the Atlantic Ocean forces the location of extra-tropical transitioning storms northward late in the season so here in Ireland, we are more likely to see the remnants of these storms influencing our weather over the coming weeks and months.

Image from the National Hurricane Center showing the average spread of storms during the season, with the peak of season on September 10^th.

Met Éireann Podcast

For further information on Hurricanes, have a listen to our Met Éireann Podcast on Hurricanes with National Hurricane Center Senior Hurricane Specialist, John Cangialosi.

https://www.met.ie/education/podcast

For the latest satellite imagery, visit:

https://www.star.nesdis.noaa.gov/GOES/sector_band.php?sat=G16&sector=taw&band=13&length=24

https://www.met.ie/latest-reports/satellites/world-infrared

For the latest weather outlook for Ireland, go to:

https://www.met.ie/forecasts/national-forecast

Works Cited in this commentary:

A second named storm in August

Meteorologist Commentary by Joan Blackburn (Deputy Head of Forecasting) and Sinéad Duffy, Met Éireann, Monday 24th August 2020

Storm Francis was named by the UK Met Office due to expected impacts in the UK as a result of the second unseasonable storm in August 2020.

Storm Francis is expected to cross Ireland during Tuesday morning 25 August 2020.

Over Ireland the main concern is for intense rainfall over short periods of time. Orange level rainfall warnings are in operation for Connacht, Donegal, Cavan and Monaghan and also for Southern Coastal Counties of Kerry, Cork, Waterford, Wexford with status yellow rainfall elsewhere. Some flash flooding is likely in places and also this rainfall will further elevate river levels and may result in river flooding as well. The intense rainfall is likely to ease off in southern counties by early Tuesday morning.

It will be very windy, possibly stormy, for a time Tuesday mainly in parts of the south and southeast with yellow wind warnings in operation for Munster and for counties Wexford, Wicklow and Dublin with potential for some damaging gusts.

Caution is advised. With trees in full leaf and many on holidays across the country, impacts could be significant with the potential for damaging winds, heavy rain, and flooding in affected areas.

Tourists in exposed locations in particular will be at risk.

Please sign up for warnings notifications on the Met Éireann app and get the latest warnings  https://www.met.ie/warnings and www.metoffice.gov.uk

Figure 1. Rain and Wind warnings associated with Storm Francis (as at 7pm 24th August 2020)

Storm Francis is forming in the Atlantic to the southwest of Ireland as a low pressure deepens rapidly. The extensive bands of cloud and rain are approaching quickly.

Figure 2. EUMETSAT animation of Storm Francis on 24th August 2020

The warnings may be updated as the forecast models are updated, so please keep up to date on the website and apps.

https://www.met.ie/warnings

https://www.met.ie/forecasts/national-forecast

https://www.met.ie/forecasts/marine-inland-lakes/sea-area-forecast

Figure 3. Met Éireann's high-resolution Ensemble Prediction System (IREPS) showing the range of possibilities of 24 hour rainfall amounts.

Climate perspective

As our planet warms, so does our atmosphere. Warmer air has the ability to hold more moisture. Here in Ireland we have seen an increase in average annual rainfall by about 6% over the last 30 years as compared to the previous 30 years. The latest climate model projections suggest Ireland will likely see more frequent heavy rainfall events, as our planet continues to warm.

Named Storms

Storm Francis is the sixth named storm from the 2019/2020 storm list of the Met Éireann, UKMO and KNMI partnership. It is the ninth named storm overall.

The first one, storm Lorenzo, was named by the National Hurricane Center in the USA. Lorenzo originated as Hurricane Lorenzo, the eastern- and northern-most category 5 hurricane ever recorded in the Atlantic Ocean but it weakened considerably as it stalled off the northwest coast and produced few impacts as it tracked over Ireland on Friday 4th October 2019.

Storm Elsa (18th December 2019) and Storm Jorge (29th February 2020) were named by the IPMA, the national meteorological service of Portugal, and AEMET, the national meteorological service of Spain, due to their forecasted impacts in the Iberian region.

Figure 4: Storm names for 2019/2020 season

Storm Ellen brings unseasonably wet and stormy August weather

Meteorologist’s Commentary by Evelyn Cusack, Head of forecasting, Met Éireann Tuesday, 18^th August 2020

Met Éireann has named Storm Ellen for disruptive and potentially damaging winds Wednesday evening (19th) and throughout Thursday (20^th). Due to the combination of storm surge, spring tides and onshore winds there is a risk of some coastal flooding. There is a risk also of some inland and river flooding with some potentially heavy, thundery downpours.

Status Orange/Yellow wind warnings are in effect for the Island of Ireland and will be updated Wednesday morning. Orange level impacts may potentially occur over any part of the Island and tourists in exposed locations in particular will be at risk for these unseasonable stormy and wet conditions. Please sign up for warnings notifications on the Met Éireann app and get the latest warnings https://www.met.ie/warnings and www.metoffice.gov.uk

Figure 1: Warnings for Ireland issued Tuesday 18/08/2020 for Wednesday/Thursday

Storm Ellen is forming over the Atlantic fuelled by the remnants of Tropical Storm Kyle as shown here in Figure 2 which is a display of Airmass temperature and satellite imagery from the European satellite, Meteosat.

Figure 2: A large circulation in mid-Atlantic fuelled by the interaction of the remnants of tropical storm Kyle and the jet-stream.

Ellen is forecast to move over the southwest of Ireland Wednesday evening, tracking northwards over the country during Wednesday night and daytime Thursday. Gusts generally of 80 to 100km/h can be expected and potentially gusts may exceed 130km/h in some exposed coastal and mountain locations and some lower locations due to funnelling effects.

https://www.met.ie/forecasts/atlantic-charts/precipitation-pressure

Figure 3: Storm Ellen is forecast to track in over Ireland from the Atlantic

There is still a high degree of uncertainty in the exact track of the storm and there is a considerable spread in possibilities over Ireland with some models indicating that the east may get the strongest winds. The warnings will be updated Wednesday morning but here is the 18Z run of the Met Éireann high-resolution model, HARMONIE. It is an ensemble prediction system (IREPS) with 11 different possible tracks and outcomes. Orange level impacts may potentially occur over any part of the Island.

Figure 4: Met Éireann's high-resolution Ensemble Prediction System (IREPS) showing the range of possibilities of the severe winds.

With trees in full leaf and peak numbers on holidays in Ireland, impacts could be significant with damaging winds, heavy rain, and large waves along the coast. Strong winds overland, high, potentially dangerous, waves can occur on lakes as well as along coasts and over high ground.

Storm Ellen is the fifth named storm from the Met Éireann, UKMO and KNMI storm list of 2019/2020. It is the sixth named storm overall as the first one, storm Lorenzo, was named by the National hurricane Center. Lorenzo originated as Hurricane Lorenzo, the eastern most and northern most category 5 hurricane ever recorded in the Atlantic Ocean but weakenend considerably as it stalled off the northwest coast and produced few impacts as it tracked over Ireland on Friday October4^th 2019.     

Figure 5: Storm names for 2019/2020 season

Figure 6 is the Storm naming form Met Éireann shared with its partners the UK Met Office and KNMI, the Dutch Meteorological Service in the West group and the Southwest group consisting of Portugal, Spain, France and Belgium when we named Storm Ellen.

Figure 6: Storm Naming Form for Storm Ellen

Updates will be issued Wednesday morning. Extreme caution is advised.

https://www.met.ie/forecasts/marine-inland-lakes/sea-area-forecast

https://www.met.ie/warnings

https://www.met.ie/forecasts/national-forecast

Published Friday 14th of August

During the last week, Ireland, and to a much more exceptional extent our neighbours in southern Britain, have been experiencing very warm and humid conditions. This has been due to very warm or hot air over the European continent being transported northwards over our part of the world.

But that hot continental air has had low pressure associated with it. The combination of low pressure and warm humid air produced conditions that triggered thunderstorm activity. Torrential downpours and frequent thunder lightning occurred over southern parts of country on Wednesday night.

Another aspect of the conditions over the last week has been the generally light winds associated with what meteorologists would describe as a slack pressure pattern. The low pressure that has been affecting us hasn’t been particularly low – varying between 1010 and 1014 hPa - and rather than a tightly coiled feature that we would tend to witness with a storm system, the pressure pattern over us looks kind-of bland with big spaces between the isobars and accordingly, generally light winds.

06z Analysis on Thursday 13 August 2020

Where Thunderstorms have formed, they have been quite slow-moving - because of the light winds -and they have therefore managed to dump some high rainfall amounts leading to significant spot flooding.

There will be little change in the pressure pattern out to around Tuesday next week so the risk of heavy or potentially thundery downpours will remain until then, with the exact detail varying day to day and dependent on parameters like cloud cover and daytime heating.

Later Next Week:

Looking ahead to around midweek next week, we have to look further afield. And our meteorologists are keeping an eye on developments in the Atlantic. Currently we’re following a low pressure area which is expected to form southwest of Greenland (A in the picture below) and how that is going to interact with another feature which is currently off the coast of North Carolina (B in the picture below).

ECMWF Surface Pressure Chart over-layed with 850hPa temperatures for Saturday 15 August

The “B” system has attracted the interest of National Hurricane Center forecasters who are monitoring it for tropical development:

Regardless of what ends up happening, the interaction of the cold air coming down from Greenland and the relatively warmer air coming off the east coast of the US, is likely to result in a powering up of the Jet Stream across the Atlantic. With a strengthening of the Jet Stream, the return of an Atlantic-influenced westerly or south-westerly regime seems likely by around midweek next week, with Atlantic low pressure likely to bring spells of rain and noticeably windier conditions than of late.

The Year So Far 

Written by Paul Moore and Valerie Watters.

A very strong Stratospheric Polar Vortex leading into February helped to ignite the North Atlantic Jet stream, which brought numerous deep depressions towards North-western Europe. This led to a very wet and very windy month in Ireland, with temperatures a little above average overall.

As the Stratospheric Polar Vortex began to wind down during March, the North Atlantic Jet stream also became less active, and moved further away from Ireland during the second half of the month. This led to a split, with the first half of March still seeing a lot of low pressure and rain, whereas the second half saw more in the way of high pressure and dry weather.  Rainfall amounts ended up below average for the month overall, and temperatures also were below average.

April and May saw blocking high pressure in charge for the most part, with a weakened or split Jet stream steered away from Ireland to the north or south into the Mediterranean. This led to both April and May being very dry and mild months, with drought conditions in many places.

A pattern flip at the beginning of June pushed the blocking high pressure away, leading to an unseasonably strong Jet stream dominating our weather for the months of June and July. This has led to above average rainfall for both months, and near to, or below average temperatures.

Fig 1 - Rainfall amounts for the year so far.  Note that the July data, provisionally at 122% of normal (1981-2020), is up to 29^th of July.

Outlook

High pressure building from the Azores over the weekend will work in conjunction with high pressure over Europe to break down the jet stream, introducing dry and settled conditions over the country.  Rainfall amounts for the coming week will be well below average, although there is potential for some thundery downpours during the early days of next week in eastern parts of the country, which we will be monitoring closely in the coming days.  Temperatures will be above average for this time of year, with maximum temperatures in the low twenties, and winds will be light.

Fig 2 – Forecast maximum temperatures across Ireland from the ECMWF model for Saturday the 8th and Sunday the 9th of August.

Funnel Cloud Observed in Tipperary

One of the funnel cloud photos sent to us by Martin O'Brien

One of our Twitter followers, Martin O'Brien, tagged us in a series of 4 photos which clearly show a well-formed funnel cloud. He took these while passing through the scenic Blueway region in Carrick-on-Suir, Tipperary on Saturday afternoon 9th May, during this period of convection described below by Alan Hally.

Paul Downes, Forecast Meteorologist, Central Forecasts and Applications Office, Met Éireann, provided the following explanation.

This funnel, while not reaching the ground is a great example of the conservation of angular momentum. There are three main ingredients needed to get this.

1. Moisture. While you might not see it until it transforms into a cloud, moisture is all around us. The more humid the air the more moisture that is being suspended in the air. Saturday was a warm humid day.
2. Instability. Like a hot air balloon, the air inside a cloud has to be warmer than the air outside it, so when the sun heats the earth, 'bubbles' of warm air rises.

The air in the cools as you go up in the atmosphere, e.g. when you see ice crystals grow on the outside of an air plane window- its very cold out there! But the rate at which it cools is always changing. The air in the 'bubble' will cool too at a constant rate as it rises, the key here is if it cools slower than then atmosphere, we call this instability. The atmosphere is unstable and the bubble can continue to rise.

At a point called the Tropopause, approximately 10km above our heads, the atmospheric temperature begins to rise again and the air becomes stable once more. So If you have (1) moisture then as the invisible bubble rises and cools it will eventually condense into a cloud. If it is still unstable the cloud will continue to rise into a cumulonimbus  (cumulus- a towering cloud, nimbus - with rain).

So that is what starts the process. The final ingredient is:

3. Shear. This can have several forms but for now we will just look at directional shear. If winds change direction along a front, such as a sea or lake, breeze shear can exist along the front, this can cause the air to turn. Alone it will do very little and is quite common. However if you place it under an updraft (a cloud going upwards)  it acts like an ice skater in a spin. When an ice skater spins and their arms are out they rotate slowly, if they want to spin faster they pull their arms in - this is called the conservation of momentum and it works in nature just the same. If a large eddy of rotation exists along a boundary and a shower accelerated the air upward, it will tighten the rotation below it. This causes pressure to decrease and to condense, thus forming the funnel cloud we see in the photo above. In extreme cases it can produce powerful tornadoes. However more of every ingredient would be needed- which is something we rarely ever see here- as well as a lot of help from the jet stream which didn't really play a major role on Saturday.

Convection in Ireland: Thunderstorms on Saturday the 9th of May 2020
by Alan Hally, Meteorologist in the Research, Environment and Applications Division, Met Éireann

On the 9th of May, Ireland was under the influence of a high-pressure system with temperatures in the high-teens and low to mid-twenties countrywide. Dynamically, i.e. in the highest levels of the atmosphere, there was very weak forcing due to the presence of the high-pressure. Given the location of the initial thunderstorms in the south-west, orographic forcing (i.e. upwards motion of air due to mountains) was likely a very important contributory factor to these thunderstorms. The atmospheric conditions followed a conceptual model known as "convection in fair weather conditions". Using a combination of satellite photos and vertical cross-sections of the atmosphere, we can get a very clear picture of what was occurring on Saturday the 9th of May.

In order for a surface based thunderstorm to occur, the dew-point temperature must be 12C or higher. Figure 1 below shows a satellite photo of Ireland at 1pm on Saturday the 9th of May in the infra-red along with an overlay of the 12C dew point isotherm (in purple) from an analysis provided by the European Centre for Medium Range Weather Forecasts (ECMWF) weather model. This clearly illustrates that Munster was perfectly primed for the development of strong thunderstorms.

Figures 2 (a), (b) and (c) are what we call vertical cross-sections. These figures demonstrate respectively; rising motion (known as omega), convergence/divergence (very important for illustrating areas where thunderstorms can occur) and relative humidity. These images detail the conditions of the atmosphere from the surface up to a height of approximately 12km. Image 2 (a) displays a large area of red from approximately 1000hPa to 300hPa. This represents the very strong updrafts, or upward motions of air in the atmosphere. Images 2 (b) and (c) compliment this perfectly as they show both convergence of air at the surface (in red on 2(b)) and high values of relative humidity in the upper atmosphere (green lines on image 2 (c)). The combination of all these factors; the mountains of the south-west, the high dew-point values, the strong rising motion and the moist air in the upper atmosphere led to very heavy downpours throughout the afternoon of Saturday the 9th of May. A satellite animation of the development of the storms can be seen below in what is known as the "Day Natural Colours RGB". The presence of tall convection producing cumulonimbus clouds can clearly be seen by the blue/cyan colours in Munster and areas over the south-east.

Figure 1: Ireland at 1pm on Sat. 9th of May in infra-red, 12C dew-point isotherm in purple

Figure 2 (a): Rising motion in red and equivalent potential temperature values in solid black lines. The equivalent potential temperature values decrease from the ground to around 500hPa, a further indication of the likelihood of convection

Figure 2 (b): Convergence of air at the surface (in red) and divergence of air higher up in the atmospshere (in blue)

Figure 2 (c): Relative humidity through a vertical layer of the atmosphere from the surface up to 200hPa. Green lines indicate values above 80% relative humidity.

Day Natural Colours RGB. The satellite image loop that shows the thunderstorms bubbling up from 06UTC to 18UTC in steps of 3-hours

Please see below thunderstorm activity, mostly over Munster this afternoon. ⛈️

Lightning strikes, when they occur, are displayed as a cross. Initially they are red but change to orange and then yellow after a period, then disappear.

For more info visit: https://t.co/YJqxvBBwTs pic.twitter.com/3ot01s5fmU

— Met Éireann (@MetEireann) May 9, 2020

By Dr Rónán Darcy & Dr Noel Fitzpatrick, Research Division and Evelyn Cusack, Head of Forecasting Division.
Met Éireann has launched a significant upgrade to the forecast system it uses to help predict the weather. This upgrade will aid our forecasters in their day-to-day duties and open the way to providing earlier warnings for severe weather events. The system has been developed and tested by Met Éireann staff over the past several months, and has been implemented as part of a new computing collaboration with the Dutch weather service, KNMI.

Numerical Weather Prediction (NWP) refers to the use of computer models to predict the weather, and forms the basis of modern forecasting. In recent years, national weather services and researchers have been developing and utilising an enhanced form of NWP known as Ensemble Prediction Systems (EPS).
The Met Éireann Podcast - Chaos and Computing in Weather Forecasting

While traditional weather models produce a single forecast for a given time (known as a deterministic forecast), ensemble systems produce multiple forecasts or possible outcomes for the same time period. Forecasters can then examine this range of possible forecasts to answer questions such as how likely is a given weather event (i.e. do most of the forecasts show a similar outcome or do they disagree significantly), what is the possible range of values for a weather variable like wind, temperature etc., or how much uncertainty is there in the location or timing of a storm’s arrival.

Essentially, this method marks a substantial increase in the information available to forecasters in terms of the probability of occurrence, severity and timing of given weather conditions, information that is particularly important in the build up to potentially high-impact weather events.

In 2018, Met Éireann developed its first ensemble-based NWP system, known as the Irish Regional Ensemble Prediction System (IREPS). Originally run twice per day, this system produced 11 forecasts (known as members) for weather conditions over the next 36 hours. On April 15^th 2020, the IREPS system was upgraded to a 54-hour, 11-member ensemble which is run four times per day. This will help increase how frequently our forecasters are updated on changing weather events and aid in lengthening forecast and warning times.

Technical details

KNMI Supercomputer has a capacity of 50 trillion calculations/sec (50 teraflops). HARMONIE requires around 3 quadrillion calculations

Due to the vast amounts of calculations and data that must be processed to simulate the atmosphere, large, high performance computing (HPC) systems are required to run NWP models with the necessary accuracy and timeliness. Met Éireann uses computing resources on the HPC system of the European Centre for Medium Range Weather Forecasts (ECMWF) to run its NWP models. To meet the additional computing resources required to realise the latest upgrade to IREPS, Met Éireann has established a collaboration with the Dutch national weather service, KNMI. The newly acquired resources on the KNMI HPC system have been combined with the existing resources at ECMWF, providing sufficient computing power to run the enhanced system.

IREPS is an ensemble which uses the HARMONIE-AROME model configuration (version 40h1.1) of the shared ALADIN-HIRLAM NWP system (hereafter HARMONIE-AROME). It consists of 10 ensemble members with 1 control member. The control member and the 10 ensemble members produce 54-hour forecasts and run four times daily at 00 Z, 06 Z, 12 Z, and 18 Z. IREPS runs with a horizontal grid spacing of 2.5 km, a spatial extent of 1000 x 900 grid points (see figure below), and 65 vertical levels. Both conventional (observations from weather stations, ships, buoys, balloons and aircraft) and scatterometer (satellite wind data) observations are assimilated or ingested into the model.

The geographical area over which Met Éireann runs its operational NWP forecasts is highlighted in colour.

The ensemble members are constructed using a combination of boundary condition perturbations and perturbations applied to surface parameters in the model. The boundary condition perturbations follow the Scaled Lagged Average Forecasting (SLAF) technique whereby older boundary conditions valid at the current time are perturbed by a scaling factor which depends on their age with respect to the current time. The surface perturbations are applied to a number of variables within the surface code in the model such as sea surface temperature and soil moisture. These perturbations are intended to account for uncertainty related to energy transfer from the model surface to the planetary boundary layer (usually the lowest kilometre of the atmosphere).

To summarize: The observations (initial conditions) and the model are not perfect. Small errors in the initial conditions of a forecast grow rapidly, and affect predictability. The ensembles provide forecasters with an objective way to predict the skill of a forecast and to estimate the most likely scenario. This will improve forecasts and warnings and enhance support for impact-based decision making for weather events and contribute to the safety of citizens and property.

What does output from an EPS look like?

The output of an ensemble prediction system may be displayed in many ways, each with their own purpose. Plots of all members are displayed side-by-side (called “postage stamps”) to give an indication of the spread in the range of possible solutions over a large area at a given time. In the below image, postage stamps for the 06 Z forecast from 16^th April indicate rainfall is likely to occur in the south-east, but the north east is more uncertain with some solutions suggesting relatively dry conditions.

Postage stamps from the 06 Z IREPS on 16th April 2020 showing rainfall predicted up to 54 hours later - between 09 Z (10:00 local) and 12 Z (13:00 local) on the 18th April 2020. All eleven members (1 control + 10 perturbed) are plotted, as well as their mean.

Another method combines all members together to form a single pseudo-probability plot based on a threshold. In the image below, the number of members exceeding 5 mm of rainfall in 6 hours are counted, giving an indication of the probability of this threshold being exceeded over the area plotted.

A pseudo-probability plot for rainfall totals exceeding 5 mm in a 6 hour window. The raw data has been upscaled to 5x5 grid points to avoid the double-penalty issue seen with high-resolution ensemble prediction systems.

Yet another method is the use of meteograms. Here, a time-series plot is produced for a specific parameter at a single location to visualise how each of the ensemble members progress. This gives an indication of the spread, and identifies “clustering”, where several members may bunch around a particular solution.

A meteogram time-series plot demonstrating the evolution of the temperature forecast at Dublin Airport for each of the 11 members of an IREPS forecast

Case Study 1: Ophelia Monday 16th October 2018

Prior to Ophelia only the deterministic forecast (a) was available from HARMONIE-AROME. The track of Ophelia was re-run using the 10-member ensemble system (b). While the deterministic track was very close to the observed track, had the IREPS been available 54-hours ahead it would have given more certainty to the forecasters particularly helping to provide a longer lead-in time in the issuing of the Status Red wind warnings.

(a) Projected track of the central low pressure of Ophelia over a 24-hour period from the operational run of HARMONIE-AROME at 0000 UTC on the 16th of October.
(b) Projected track of the central low pressure of Ophelia over the same period for each of the ensemble members of IREPS – this illustrates the confidence we could have in the track of Ophelia.

Case Study 2: Thunderstorms, Saturday 9th May 2020

Saturday the 9^th May 2020 was a warm, humid day with temperatures up to 24 degrees. Thunderstorms with hail developed in the afternoon. The white map of Ireland is the afternoon radar on the 9^th showing intense showers/thunderstorms. The other 11 green maps are the showers as forecast by our new 54-hour IREPS from a forecast on the evening of Thursday the 7^th, each one being a possible outcome.

The overall IREPS forecast was excellent. However the 10 ensemble members show the different locations possible illustrating how difficult it is to pinpoint exactly where showers will develop and how difficult it still is to give thunderstorm warnings for exact locations two days ahead.

Some cumulus congestus on their way to becoming cumulonimbus thunderstorms at Thurles, Co Tipperary Saturday morning, 9th May. Photo by Dr Emily Gleeson, Research scientist Met Éireann.

You can listen to Rónán Darcy and Alan Hally talking about setting up IREPS and its benefits for weather forecasting.

Further plans to 2023

Met Éireann’s operational NWP team from top left; Colm Clancy, Rónán Darcy, Alan Hally and below, NWP team leader, Eoin Whelan

The upgrade to IREPS is thanks to the development of the system by our Met Éireann NWP team led by Eoin Whelan and the substantial installation and testing work performed by them over the last several months. In addition, personnel from Technology, Forecasting, and Business Services Division were involved in testing and implementing the necessary technical changes and in managing the agreements and approvals required for our collaboration with KNMI.

The next stage in Met Éireann's HPC projects will see us collaborate with Denmark, Iceland, and the Netherlands to develop a common numerical weather prediction system. Known as UWC-West, this project is due to go operational in 2023 and preparations are well underway with most non-shift staff in Met Éireann remote working at this time.

by Gavin Gallagher, Meteorologist, Met Éireann

An Update on Recent Rainfall Measurements and the Rainfall Forecast, Recent Drought conditions, Pollen & Sunburn.

Low Rainfall levels for March and thus far in April have brought drought and an increased risk of forest fires.

The majority of monthly rainfall recordings across the country were below their Long-Term Average for the month of March, as high pressure dominated our weather from mid-month. The lowest relative rainfall being 56% of the expected monthly rainfall at Moore Park, Co Cork, with a monthly rainfall total of just 47.9 mm.

The much drier than normal weather from the midpoint of March to mid-April has led to meteorological ‘Dry Spells’ and ‘Absolute Drought’ conditions in parts of Ireland. A dry spell is defined as “A period of 15 or more consecutive days to none of which is credited 1.0 mm of precipitation”, while absolute drought conditions in Ireland are defined as “A period of 15 or more consecutive days to none of which is credited 0.2 mm or more of precipitation.”

Recent Dry spells have been recorded at the following stations:

Absolute drought has recently been recorded at the following stations:

Above is the recorded rainfall for Dublin Airport for the month of March. The green line is the long term average (or expected) rainfall. The red lines are the daily rainfall amounts, with blue being the cumulative rainfall. Note the near zero rainfall from mid-March.

Find the graph for your local area here:

https://www.met.ie/climate/past-weather-statements

Choose “Rainfall Graph” from the menu.

Above is the cumulative rainfall for Athenry in Co. Galway for the past 20 days. The pink line is the long term average (or expected) rainfall, the blue line is the actual amount received and the light blue/green lines is the range of rainfall forecast (from our model ensemble) over the next 10 days. This shows that rainfall is well below expected values and will remain so for the coming 10 days.

Past 7 Days Rainfall:

Rainfall totals were below average across the entire country in the past week. Largest relative totals of up to 86% of normal were measured in inland parts of southern Leinster, however most areas received only 10 to 50% of average rainfall for this time of year, mainly resulting from rainfall last Sunday, April 5th.

Forecast Rainfall (Fri April 10 to Fri April 17) :

Areas in the west and north of the country will receive rainfall today, Friday, and again tomorrow Saturday, while it will remain mostly dry elsewhere. All areas will likely see rainfall on Sunday, before high pressure dominates our weather again from early next week, heralding another period of mostly settled, mostly dry weather.

Below, is the forecast rainfall (mm) for the next 7 days out to midday Friday April 17^th. Most of this rain will fall this Sunday April 12^th.

The longer range forecast for late April and early May is for our weather to be drier than normal with below average rainfall.

It is worth noting that with rainfall below average, the danger of forest fires / gorse fires burning out of control, increases

U.V.

As we approach the midpoint of spring, the sunlight we receive becomes noticeably stronger, with harmful UV rays causing sunburn. People may be surprised to get sunburn in early April, but it’s helpful to remember that the sun is as strong in Ireland in April as it is in August. Sunlight is at its strongest at the summer solstice in June, then it is as strong in May as it is in July, as strong in April as it is in August and so on. So even though it may not be as warm in April as in August, the sun is just as strong, and you will still burn when exposed to the sun.

Also, the ozone hole over the Arctic is at its biggest (most damaging) at the end of winter and during spring, allowing more harmful UV rays to reach the surface.

Below, is the UV measurement from one of our Brewer Spectrophotometers (an instrument which measures ozone, and computes the UV level). This one is at Valentia Observatory in Co. Kerry, and the UV Index today is low due to cloud cover.

Daily U.V. forecasts will be issued by Met Éireann and be available on our website and social media from Tuesday April 14^th.

Pollen:

Tree pollen peaks in Ireland in March and April with grass pollen at its peak from May to August. Daily pollen forecasts will be issued by Met Éireann and be available on our website and social media from Tuesday April 14^th.

by Joanne Walker, Met.ie website/app manager, Digital Communications Unit, Forecast Division

This year it focuses on Climate and Water

World Meteorological Day showcases the essential contribution of National Meteorological and Hydrological Services to the safety and wellbeing of society. This work continues 24/7 despite the challenges and constraints of the pandemic.

“We feel the effects of climate change mostly through water: more floods, more droughts, more pollution. Just like viruses, these climate and water-related shocks respect no natural boundaries,” said WMO Secretary-General Petteri Taalas.

”The world needs to demonstrate the same unity and commitment to climate action and cutting greenhouse gas emissions as to containing the Coronavirus pandemic,”  he said.

“Changes in the global distribution of rainfall are having a major impact in many countries. Sea levels are rising at an increasing pace, driven by melting of the largest glaciers, like in Greenland and Antarctica. This is exposing coastal areas and islands to a greater risk of flooding and the submersion of low-lying areas,” said Mr Taalas.

Taken from the WMO World Met Day 2020 press release, available here.

• This week our Met Éireann app will be updated allowing you to set up and receive Push Notifications of all Marine Warnings for Ireland.
• Met Éireann provide climate information services which promote the safety of citizens and supports economic and environmental resilience.
• Met Éireann is developing a Flood Forecasting Warning Service in conjunction with the OPW.

Weather is so much a part of our everyday life that access to high quality information on the weather is expected or taken for granted as a normal convenience of modern life — whether it’s a storm or a flood that threatens life and property, fog or icy conditions that disrupt road transport or air traffic, or just a minor inconvenience due to summer showers. The changing climate and, the increased frequency of extreme weather events, in tandem with increased urbanisation, is making Ireland more vulnerable to the impacts of weather. Since our beginnings over 80 years ago Met Éireann has been serving Ireland by providing public weather information, forecasts and warnings to help protect life and property. Over the next decade we will rise to the growing challenges of climate change by supporting Ireland in becoming weather and climate prepared.

Marine Services

Met Éireann produces specialised sea area forecasts for Irish coastal waters and inland lakes, and our wave height forecast map. We work closely with the Coastguard and other agencies in the protection of life and property. Met Éireann has produced a number of reports into how climate change will affect water levels around the coasts.

Our Marine Climatology page contains graphs of buoy data since they were installed and the record of average monthly sea temperatures at Malin Head compared with the WMO 30 year average period of 1961-1990.

We are currently developing a Flood Forecast Centre with the OPW to assist the public and the emergency services in preparing for major flood events.

Met Éireann actively promotes Water Safety particularly during the key summer months with a permanent link on our homepage to Water Safety Ireland and our Water Safety information and advise article.

Climate Services

Air Masses

In the Climate menu of our website you can learn all about the Climate of Ireland, read up on our work on Climate Change, view the Weather Extreme Records for Ireland and download reports on Major Weather Events in Ireland.

The Past Weather Statements page contains a vast archive of monthly, seasonal and annual weather summaries along with daily values and rainfall, temperature graphs.

Our Climate Services are focused on the timely production and provision of high quality data (observational data, gridded data, scientific analysis, etc) and products to decision makers. In order to support Irish society at large and facilitate the development and evaluation of adaptation and mitigation strategies for Ireland.

Oak Park Weather Station, Carlow

Our Available Data section contains graphs of Daily Data and Monthly Data from all our weather stations, you can also download Historical Data from those stations and our voluntary observer stations. Read all about MÉRA- our Climate Re-Anaysis project, and view the 30 Year Averages- the WMO recommend that climate averages are computed over a 30 year period of consecutive records.

What does a weather station look like? Photos and details of all our weather stations- and webcams images- are available here.

View the archive of Lightning strikes over Ireland on a map, download available.

WOW-IE

WOW-IE map

WOW-IE is the Weather Observations Website of Met Éireann and is part of the global WOW network of crowdsourced weather observations. It is available at wow.met.ie  If you own a weather station we invite you to connect it to the WOW database and view the data online. You can view real-time temperature, pressure, wind values and more from privately-owned weather stations, Met Éireann’s stations (including half hour observations) and from National Meteorological Services around the world!

WOW-IE is a Weather Education and Data Comparison tool. You can view the archive of past weather observations on the WOW-ie map, on a graph or table and the data is available to download. WOW-IE displays weather observations from various sources in real-time*.

WOW-IE uses the UK Met Office WOW database, as do national meteorological services in the Netherlands, Belgium, Sweden, New Zealand and Australia whose data can also be viewed on the WOW-IE map. Currently in Ireland there are about 15 private weather station owners uploading their weather observations to WOW-IE. Met Éireann uploads data from 20 of its official automatic weather stations and over 30 of its new automatic climate stations. By sharing your weather station data you are helping to improve the Irish weather observing network and helping Met Éireann forecasters to get a better picture of weather around Ireland.

*Met Éireann does not correct or review WOW data, hence incorrect values or missing data may occur, even from official stations. Quality controlled data from Met Éireann’s official weather stations are available here.

Click to view Met Éireann's strategy statement

Storm Jorge from Space – Saturday 29th of Feb, 2020

By Conor Lally (Meteorologist, Observations Division)

Presented are a series of three satellite images detailing the progression of Storm Jorge (pronounced Hor-hay), the seventh winter storm of the season, as it crossed the country today.

These images are Natural Colour RGB (Red Green Blue) composites courtesy of the European Organisation for the Exploitation of Meteorological Satellites (EUMETSAT). Composite satellite images combine pictures taken at different visible and infra-red frequencies, each of which contains slightly different information. To highlight each picture’s own particular specialty, that is to say those features that are captured best in that particular frequency, they are tinted a different colour. Then when combined together they reveal more information than they would by themselves.

The centre of the storm Jorge, which developed in the mid-Atlantic and deepened rapidly as it approached Ireland thanks to a strong jet stream aloft, was clearly identifiable as the dark patch to the west of the country in the first of our series of satellite photos, which was taken at 9am. At this stage the pressure in the centre of the storm was predicted to be in the region of 950 hPa and the closest of our stations to the centre of the storm, Belmullet in Co Mayo, recorded a Mean Sea Level pressure of 963 hPa.

Despite the proximity of the storm centre we can also see that Saturday started off as a bright clear day for many with an absence of cloud for much of the eastern half of the country. However, the storm quickly began make its presence felt shortly after sunrise on the west coast, as a swathe of storm force winds began to drive in across the west of the country by which time our station in Mace Head had already recorded a wind gust of 92 km/hr.

We can see in the second image taken at 11 pm the storm’s occluded front, which was visible as the thick band of cloud in the shape of a comma head that is wrapped around the storm’s centre, push its way into to the middle of the country. With the front came heavy rain but also for a short while some sleet and snow along its leading edge. Our station in Knock airport recording 3 cm of snow lying by 11 am. Looking carefully at our composite image we can just discern this band of frozen precipitation as a light blue streak to the right of the thick white and warmer cloud of the front. The tip of the comma head often contains much of the highest winds and this is evident in the winds recorded at this time with Mace Head, Newport, and Athenry recording gusts of 133, 102 and 98 km/hr.

In our third image taken at 1 pm, the front has spread across the whole of the country and ‘Jorge’ now shows signs of a maturing system. What was in our first image the tight core of the storm centre has become elongated as cold air, visible in the picture as the dark clear sector east and south of Ireland, was dragged into the centre. This has the effect of cutting the storm off from the supply of warm air which drives it and thus reducing its intensity.

Storm Jorge: highest ten minute means and gusts

Meteorologist’s commentary issued at 6pm Thursday 27^th February 2020

by Joan Blackburn (Deputy Head of Forecasting Division), Sinéad Duffy (Meteorologist, Technology Division) and Eoin Sherlock (Head of Flood Forecast Division) on Thursday, 27^th February 2020

Storm Jorge (named by AEMET, the Spanish meteorological service) is the latest in a series of Atlantic storms this month and is due to affect Ireland from early Saturday. Rain will extend countrywide from the west tonight, before the storm arrives.

The Meteorological Situation:

Storm Jorge (pronounced Hor-hay) is a storm centre which will undergo rapid cyclogenesis in the mid-Atlantic during Friday 28th February as it tracks northeastwards towards Ireland. It is then expected to fill slowly as it crosses over the north of the country during Saturday 29^th February. Figure 1 shows the forecast position of Storm Jorge and its associated fronts at 12 midday on Saturday.

Figure 1. Forecasted position and fronts of Storm Jorge at midday Saturday 29th February.

Storm Jorge is forecast to bring severe winds to western and northwestern coastal counties (orange wind warning) and less severe winds to the rest of the country (yellow wind warning) from Saturday morning into early Sunday morning.

Spells of heavy rain associated with Storm Jorge will worsen the flooding situation across the country. A yellow level rainfall warning will come into operation for Munster, Connacht and Donegal from tonight (Thursday night) to late on Saturday evening.

The animation in figure 2 below shows the position of the strong Atlantic jet with the corresponding deepening of the storm centre from early Friday morning to early Sunday morning.

Figure 2. Forecast position of the Jet stream during Storm Jorge

Figure 3 shows the wind field from the Harmonie high-resolution weather model for early Saturday morning, the start of the orange warning for Mayo, Galway, Clare and Kerry.

Figure 3. Wind warning forecast from the Harmonie weather model at 6am Saturday 29th February

Storm Jorge is the seventh named storm of the season. It was originally named by AEMET, the Spanish national meteorological service, due to the impact of the storm’s active cold front which is forecast to bring severe gusts and strong waves to the northwest of Spain.

Here’s the list of the winter storms so far this season:

1. Lorenzo, 4^-Oct-2019 (Ex-hurricane, named by the NOAA National Hurricane Centre in the USA)
2. Atiyah, 8-Dec-2019
3. Elsa, 18-Dec-2019 (named by IPMA, the national meteorological service of Portugal)
4. Brendan, 13-Jan-2020
5. Ciara, 9-Feb-2020
6. Dennis, 16-Feb-2020
7. Jorge, 29-Feb-2020 (named by AEMET, the national meteorological service of Spain)

Storms are named to aid the communication of approaching severe weather, helping the public to be better placed to keep themselves, their property and businesses safe. Met Éireann are part of a western Europe storm-naming group which includes the Dutch meteorological service, KNMI and the UK’s meteorological service UKMO. The national meteorological services of Spain, Portugal, France (MeteoFrance) and Belgium (RMI) are part of a southwestern Europe storm-naming group which has a separate list of names allocated to the Winter 2019/20 storm season. When a storm has already been officially named by another national meteorological service or the US National Hurricane Centre, that storm name is retained.

Flooding issues

1. A) Elevated river levels
   Currently river levels are elevated across the country, particularly in the Midlands (Shannon catchment). Levels across the Northern half of the country are also high. Therefore, additional rainfall over the coming days will compound the flooding issues here.
2. B) Coastal Flooding
   We are in a period of transition between Spring (High) Tides and Neap (Low) Tides. This means there will not be a large variation between high and low tides. The combination of high seas and strong winds or stormy conditions associated with Storm Jorge may increase the possibility of coastal flooding, especially in flood-prone areas along the Atlantic coast on Saturday (particularly when coincident with high tides).

 Keep up to date

As forecast confidence improves over the coming days Met Éireann will issue warnings as required. Please check for updates on https://www.met.ie/warnings.

Push notifications for all weather warning levels (yellow, orange and red) for your location are available on the latest version of the Met Éireann App.

Latest February Analysis 2020 updated at 10am, Wednesday 27th February 2020 by Paul Moore, Aidan Murphy and Sandra Spillane, Climate Services

A strong Stratospheric Polar Vortex, coupled with the troposphere, has led to the North Atlantic Oscillation being in a strongly positive phase during February 2020. This has resulted in a zonal pattern across the Atlantic with a strong Polar Jetstream, further south than normal, bringing a series of vigorous Atlantic depressions, towards or just to the north of Ireland. These depressions, including two named storms, Ciara and Dennis, brought prolonged periods of heavy rainfall and stormy weather leading to extensive flooding in places, particularly along the Shannon catchment. Heavy rainfall falling on already saturated ground and with low evaporation rates in winter exacerbated the flooding.
The position and strength of the Polar Jetstream has resulted in 1.5 to 3 times the normal monthly rainfall so far for February throughout the country (a month usually associated with one of the least rainfall amounts).
The highest monthly rainfall total during the period 1-26 February was observed at Newport, Co Mayo with 306.6 mm (242 % of its February LTA). The Lowest monthly rainfall total during the period 1-26 February was observed at Dublin Airport, Co Dublin with 120.7 mm (247% of its February LTA). While the highest daily rainfall total was 51.5 mm on Saturday 8 February 2020 at Knock Airport, Co Mayo (50% of its monthly LTA).

So far this month, ten synoptic stations have already had their wettest February on record, including Phoenix Park, Co Dublin (records going back to 1850), Shannon Airport, Co Clare (record length 74 years), Newport, Co Mayo (record length 60 years), Claremorris, Co Mayo (record length 19 years), Casement, Co Dublin (record length 56 years) and Knock Airport (record length 23 years).

Full report <<here>>

Meteorologist's Commentary at 12 noon, Monday, 25^th February 2020 by Sandra Spillane PhD, Climatologist and Aidan Murphy, Climate Services 

The Weather and Climate Statements for February 2020 and Meteorological Winter 2020 (December 2019, January 2020 and February 2020) will be published on the 2nd working day and 3rd working day of March 2020 respectively. For these publications, and more, see: www.met.ie/climate/past-weather-statements.

The recent rainfall is above average at all our SYNOPTIC stations when compared to the 1981-2010 climatological long-term-average period (LTA, the World Meteorological Organisation's standard period range for weather comparisons). The provisional rainfall totals for 1-24 February are currently at 225% of Ireland's average. For comparison, December 2015 (Storms Desmond on Sat 5th,  Eva on Thu 24th and Frank Tue 29th), was around 245% of normal.

Note: the provisional value may go up or down by the end of the month, as quality control is completed on the data and as more rainfall observations come into Met Éireann. You might spot in the February 2020 maps below that there are gaps in mountain regions, the reason for this is due to their location and that rainfall totals at mountain stations are generally read once a month.

A series of vigorous Atlantic depressions affected the country in February, tracking closer to Ireland than usual and bringing prolonged periods of heavy rainfall and stormy weather leading to extensive flooding in places. The Polar jet stream extended across the Atlantic right over Ireland for most of the month, marking the tracks of successive storms resulting in 1.5 to 2.5 times the normal rainfall so far this month throughout the country.

The highest monthly rainfall total during the period 1-24 February was observed at Newport, Co Mayo with 283.5 mm (224% of its LTA). While the highest daily rainfall total was 51.5 mm on Saturday 8 February 2020 at Knock Airport, Co Mayo (50% of its monthly LTA).

Be aware of flooding and keep up to date with the latest warnings and weather forecasts for your area: www.met.ie/warnings.

The following graph illustrates Newport's cumulative daily rainfall graph for the last 20 days together with the Forecast Ensembles going into the coming week.

It is not unusual for a single highest monthly total rainfall accumulation to be in this range and higher.

Recent Highest February Rainfall Totals

• 2019: 569.9 mm at in the Cummeragh Mountains (gauge no.3), Co Kerry (216% of its LTA), 81.9 mm on Tuesday 19 February 2019 at this station
• 2018: 305.9 mm at in the Cummeragh Mountains (gauge no.3), Co Kerry (116% of its LTA)
• 2017: 400.1 mm at Beenreagh Mountains, Co Kerry (164% of its LTA)
• 2016: 550.0 mm at Beenreagh Mountains, Co Kerry (225% of its LTA) with 99.5 mm on Tuesday 16 February (41% of its monthly LTA)

What is unusual is the lowest monthly rainfall total, observed at a rainfall station, to be this high. During the period 1-24 February 2020 at Roches Point, Co Cork there has been 115.7 mm total rainfall, this value is 155% of its monthly LTA (result is provisional until quality control is completed). The following graph illustrates Roches Point's cumulative daily rainfall graph for the last 20 days together with the Forecast Ensembles going into the coming week.

Recent Lowest February Rainfall Totals

• 2019: 15.8 mm at Ringsend, Co Dublin (37% of its LTA)
• 2018: 19.0 mm at Ringsend, Co Dublin (44% of its LTA)
• 2017: 28.5 mm at Clogher Head (Port), Co Louth (54% of its LTA)
• 2016: 43.6 mm at Malahide Castle, Co Dublin (100% of its LTA)

The following maps are for (provisional) 1-24 February 2020 and December 2015 when up to 943.5 mm of rainfall fell at Gernapeka, Co Cork. The lowest during that month was 149.0 mm at Malahide Castle, Co Dublin (219% of its LTA).

The following gridded maps show the observed rainfall totals across the last four February's for comparison.

Feb 2016	Feb 2017	Feb 2018	Feb 2019

To read more on the national weather records, see www.met.ie/climate/weather-extreme-records.

Latest updated Meteorologist's Commentary issued at 3pm, Friday, 14^th February 2020 by Paul Downes, Meteorologist, Forecast Division

Storm Dennis – Saturday 15^th to Monday 17^th February

Storm Dennis (as named by the UK Met Office), is currently undergoing rapid cyclogenesis in the western Atlantic. While staying to the northwest of Ireland, Storm Dennis will produce some wet and windy weather over Ireland this weekend.

The Meteorological Situation (Technical Discussion)

The strength of the jet stream is determined by the temperature gradient closer to the surface. We call the zone where warm and cold air meet the baroclinic zone (a strong temperature gradient that separates warmer air from colder air and often the battle field that spans our storms).

The ongoing battle between warm air over the south central Atlantic and a cold pool over much of eastern Canada has led to a strong level baroclinic zone fuelling a powerful jet aloft with several waves tracking across the Atlantic. The lead wave has been the driving force for this first deep low (~933 hPa) currently tracking in a northwesterly direction and occluding south of Iceland.

Warm air being pushed up along the US east coast meeting very cold air over Eastern Canada is the driving force for this powerful jet, with winds up to 225 knots (~416 km/h) at its core, currently aiding the rapid development of Storm Dennis. Dennis will develop rapidly today. Rapid cyclogenesis is defined as a drop in pressure of greater than 24 hPa in 24 hours. This storm is forecast to drop by around 70 hPa in 24 hours as it rapidly tracks north towards Iceland. With a forecast central pressure in the low 9-teens it will rival the lowest recorded pressure in the north Atlantic of 914 hPa, which occurred off the coast of Scotland on Monday 11th January 1993. The core of Storm Dennis is expected to stay well to our northwest as it rapidly strengthens, before pirouetting (the Fujiwhara effect) around Friday's low and coming back to visit us on Sunday as it slowly weakens.

View the Atlantic air mass chart animation here

Timeline for Ireland

For the latest warnings see: www.met.ie/warnings

Saturday: The first round of wet and windy weather will reach the Atlantic coast on Saturday morning spreading countrywide during the morning easing later and Status Yellow wind and rain warnings are in operation.

Sunday: The core of storm Dennis (actually a hybrid of Friday's low and Storm Dennis) will gradually fill and weaken as it tracks south-eastward towards Ireland bringing squally showers with a risk of thunder. A widespread status Yellow wind warning is likely to be issued and possibly Orange level winds locally (especially in the vicinity of squally showers along Atlantic coasts) can be expected.

Monday: Winds will gradually ease through Monday, but not dissimilar to this past Monday showery conditions can be expected with wintry conditions possible.

Flooding issues

A) Elevated river levels
Currently river levels are elevated across the country, particularly in the midlands, west and south, so any heavy rainfall would cause issues

B) Coastal Flooding
We are entering into a period of transition between Spring (High) Tides and Neap (Low) Tides. This means there will not be a large variation between high and low tides. The combination of high seas and strong winds or stormy conditions, may increase the possibility of coastal flooding especially along western and southern coasts Saturday and Sunday coinciding with high tides.

As forecast confidence improves over the coming days Met Éireann will issue warnings as required. Please check for updates on https://www.met.ie/warnings.

Meteorologist's Commentary issued at 5 pm, Friday 14^th February 2020 by Sandra Spillane PhD, Climatologist

Historic low pressures

During the storm called the 'Night of the Big Wind', barometric pressure was estimated to be as low as 918 hPa on 6 January 1839. It was the worst storm to affect Ireland for 300 years. It is also considered to have one of the lowest core pressures ever been recorded near the Irish isles.

“The two lowest barometric readings recorded in the Atlantic Ocean have occurred in the eighties and nineties of the 20th century. The first was the Atlantic Cyclone of 15 December 1986, which deepened to 916 hPa, and the other was the storm of 10-11 January 1993 which is much better documented. According to Gulev et al. (2001), Northern Hemisphere winter cyclones have intensified and produced deeper central mean sea level pressures in recent decades. However, these winter cyclones also appear to have shorter life cycles and dissipate more quickly.”

Source: http://oiswww.eumetsat.org/WEBOPS/iotm/iotm/19930111_storm/19930111_storm.html

Deep Atlantic lows, of course, may not come close to Ireland. The five lowest mean sea level pressure (MSLP) observations in the National Climate Archive are:

February's lowest mean sea level air pressures

The lowest February hourly mean sea level pressure observed at an Irish land station was 942.3 hPa at Middleton, Co Cork on Sunday 4 February 1951. The highest sustained (10-minute mean) wind speeds observed on that date was 65 km/h (35 knots, Gale Force) at Shannon Airport, Co Clare, while the highest gust (3-second mean) wind speed was 107 km/h (58 knots) at Valentia Observatory, Co Kerry during the evening. The highest 24 hour rainfall amounts around this event was:

• 67.6 mm at Waterville, Co Kerry on Saturday 3rd
• 51.3 mm at Rathdrum, Co Wicklow on Sunday 4th
• 39.4 mm at Mountrath, Co Laois on Monday 5th

For more on the storm Night of the Big Wind, see www.met.ie/cms/assets/uploads/2017/08/Jan1839_Storm.pdf.

For the national records of mean sea level pressure, see https://www.met.ie/climate/weather-extreme-records.

Meteorologist's Commentary issued by Dr Rónán Darcy, Meteorologist, Research Division on Wednesday 12th February 2020.

Storm Dennis – Saturday 15^th to Monday 17^th February 2020

Storm Dennis is forecast to track to the north of Ireland and the UK over the weekend. It will likely bring periods of very wet and windy weather, with some stormy conditions possible, particularly later Sunday into Monday.

The Meteorological Situation:

Cold air is forecast to exit Canada and enter the North Atlantic Ocean over the next few days, creating a sharp temperature gradient in the atmosphere. This will result in an intensification of the jet stream, shown in the graphics below, which will direct low pressure systems towards Ireland.

Gales are likely in coastal areas on Saturday with fresh to strong winds inland. Winds could increase further on Sunday, possibly becoming stormy, particularly along western coasts. It will be very gusty too over the weekend, with some damaging gusts possible.

Flooding issues

We are entering into a period of transition between Spring (High) Tides and Neap (Low) Tides. This means there will not be a large variation between high and low tides. The combination of high seas and strong winds or perhaps stormy conditions, may increase the possibility of coastal flooding especially along western and southern coasts due to wave transformation.

Storm Dennis may also bring very wet conditions with localised flooding possible. River levels are elevated across much of the midlands so any heavy rainfall would cause issues here.

Storm Naming

Storm Dennis is the fourth named storm of the season. The naming convention now also includes the Dutch meteorological service, KNMI as well as our existing partner UKMO. Storms are named to aid the communication of approaching severe weather, helping the public to be better placed to keep themselves, their property and businesses safe.

Keep up to date

As forecast confidence improves over the coming days Met Éireann will issue warnings as required. Please check for updates on https://www.met.ie/warnings.

Weather Warning Alerting Services

Push notifications for all weather warning levels (yellow, orange and red) for your location are available on the latest version of the Met Éireann App. Alternatively, you can also sign up to receive emails/SMS (red only) of weather warnings on our warning page. Both services are outlined here.

Cold Spell – Wintry Hazards Monday 10^th and Tuesday 11^th February

As Storm Ciara moves away today, colder air originating from Canada begins to feed down over Ireland. This will bring scattered wintry precipitation later tonight. The risk of snowfall increases during Monday and the risk will continue through Tuesday. While snow showers may develop anywhere they will occur chiefly in parts of the west and north, with some accumulations possible.

The windy conditions that the country has experienced over the last few days will persist and coupled with the colder air it will feel bitterly cold, with significant wind chill.

The animation below depicts regions of warm and cold airmasses. The warmer air is to the south of the country below the Polar Jet stream. The animation shows the much colder air moving in over Ireland over the coming days.

Airmass animation from today until Tuesday midnight

Met Éireann has wind and snow warnings in operation: (https://www.met.ie/warnings):

UPDATE

Issued 13:00, Saturday, 8th February 2020, by Evelyn Cusack, Head of Forecast Division and  Eoin Sherlock, Head of Flood Forecast Division.

Storm Ciara will pass to the north of Ireland on Sunday. It will bring extremely windy and in places stormy conditions during the morning. Southwest winds will reach gale to strong gale force in strength with damaging gusts likely.

These gusts will affect parts of the country not normally impacted by such strong winds. Gusts will typically range between 100-130 km/h but they may exceed 140 km/h locally ( see animation below).

Orange wind warnings have been issued for Storm Ciara. For full warning information please see https://www.met.ie/warnings

Flooding Issues:

We are in a period of Spring Tides and these will coincide with very high seas which will start today Saturday and will continue into next week.

The combination of Spring Tides, high seas and extremely strong winds or stormy conditions will result in a significant risk of coastal flooding especially along northwestern and western coasts. This risk will persist into the middle of the coming week.

Storm Ciara will also bring very wet conditions with localised flooding possible as intense falls of rain spread across the country with some embedded thunderstorm activity.

Wintry weather

As Storm Ciara moves away on Sunday colder air is introduced over Ireland. This will bring scattered wintry precipitation later on Sunday night. The risk of snowfall increases as we move into the coming week. While snow showers may occur anywhere they will occur chiefly in parts of the north and west.

-------------------------------------------------------------------------------------------------------------------------------------------------

UPDATE

Issued 15:00, Friday, 7th February 2020, by Evelyn Cusack, Head of Forecast Division and  Eoin Sherlock, Head of Flood Forecast Division.

Storm Ciara is expected to pass to the north of Ireland on Sunday but the country can expect some wet and windy weather before this on Saturday.

This spell of weather will bring heavy rain and strong winds, which have the potential to cause some disruption especially in western and northern counties.

The animation below displays the forecast winds for Saturday, 8th February using the Harmonie Forecast model.

As well as the heavy rain and strong winds, there is the risk of coastal and localised flooding.

As we get closer to a weather event Met Éireann's high resolution model Harmonie allows us to enhance the level of detail in our forecasts.

Met Éireann has this afternoon increased the wind warning levels for Saturday to Orange for Galway, Mayo and Donegal.

For the most up to date warnings please click here (https://www.met.ie/warnings):

Flooding Issues:

We are entering a period of Spring Tides and these will coincide with very high seas which will start on Saturday and will continue into next week.

The combination of Spring Tides, high seas and extremely strong winds or stormy conditions will result in an elevated risk of coastal flooding especially along north western, western and southern coasts. This risk will persist into the middle of next week.

-------------------------------------------------------------------------------------------------------------------------------------------------

Issued 15:00, Wednesday, 5th February, 2020, by Matthew Martin, Meteorologist, Forecast Division; Evelyn Cusack, Head of Forecasting and Eoin Sherlock, Head of Flood Forecast Division

Lá Fhéile Bríde

The first of February, marks the first day of spring in the Gaelic Calendar. The days are getting noticeably longer (dawn is an average of one to two minutes earlier in the morning and sunset one to two minutes later every evening). But in the Meteorological Calendar, which is based on average temperatures, February is the third month of winter and we can get very severe weather with the full winter range possible from heavy rain and floods to damaging wind storms, and also of course snow and ice.

Storm Ciara

Unsettled weather is expected to develop across Ireland and Northwest Europe this weekend. The change will occur as very cold air sweeps out of Canada into the North Atlantic creating a sharp temperature contrast in the atmosphere over the ocean. This temperature contrast will result in the intensification of the jet stream over the North Atlantic, which will drive vigorous areas of low pressure towards Ireland.

The animation below shows the evolution of the jet stream over the coming days.

After a period of rather quiet weather, the change to unsettled mobile conditions will occur during Friday (7^th Feb) as wet and windy weather moves in from the Atlantic. A further spell of heavy rain is expected on Saturday (8^th Feb) and this will be accompanied by strong and gusty winds with a possibility of Status Yellow warnings.

Weather conditions are expected to deteriorate further on Sunday (9^th Feb) as Storm Ciara (named by the UK Met Office on Wednesday 5th February) tracks to the north of Ireland.

Storm Ciara is forecast to be a vigorous Atlantic storm system with an expansive wind-field. Numerical Weather Prediction Models project the centre of the storm to track close to northern Scotland with a minimum central pressure of around 940hPa at lunchtime Sunday (see Figure Below).

There is a growing consensus that Sunday will be an extremely windy day across Ireland and the UK with widespread heavy rain, squally showers and with gales or storm force winds around our coasts.

Storm Ciara is the third named storm of the season. The naming convention now also includes the Dutch meteorological service, KNMI as well as our existing partner UKMO. Storms are named to aid the communication of approaching severe weather, helping the public to be better placed to keep themselves, their property and businesses safe.

Next week, conditions will remain very disturbed across Ireland and the UK. It will remain very windy and turn much colder with the chance of wintry showers and ice in some parts.

Flooding issues

The country will enter a period of Spring Tides this weekend. This will coincide with high seas, which are likely to affect coastal areas at first on Saturday but will continue into Sunday and the early days of next week. The combination of high Spring Tides and high seas as well as extremely windy or stormy conditions later in the weekend and early next week will result in an elevated risk of coastal flooding especially along western and southern coasts.

The unsettled weather is likely to produce significant rainfall totals over the weekend. This will result in an increase in river levels and may cause some localised flooding.

Keep up to date

As forecast confidence improves over the coming days Met Eireann will issue warnings as required. Please check for updates on https://www.met.ie/warnings.

Push notifications for all weather warning levels (yellow, orange and red) for your location are available on the latest version of the Met Éireann App.

Issued Sunday noon, 12^th January, 2020 by Evelyn Cusack, Head of Forecasting & Eoin Sherlock, Head of Flood Forecasting.

Storm Brendan will affect Ireland tomorrow, Monday, 13^th January bringing stormy conditions, heavy rain and high seas. Expect disruption to travel and possible localised flooding especially in coastal areas. There may also be some localised structural damage and trees uprooted.

Storm Brendan is currently off the east coast of Canada (991hPa), Figure 1, and is forecast to track eastwards across the Atlantic undergoing rapid cyclogenesis as it engages with a very strong Jet Stream. Rapid cyclogenesis is defined as a depression deepening 24hPa in 24-hours but Brendan is forecast to deepen by about 50hPa in 24-hours, Figure 2.

Figure 1

Figure 2

The following 6 images are from Met Éireann’s high resolution Harmonie forecast model. The images display the evolution of the forecast wind speeds as Storm Brendan approaches, crosses and clears away from Ireland.

The strongest winds will be initially along the west coast early on Monday morning before they spread countrywide during the morning affecting eastern counties around midday into the early afternoon. Disruption to travel and localised structural damage is possible as these winds affect the country.

During the afternoon a second core of extremely strong winds will affect parts of the west and northwest. Gusts are likely to exceed 130 km/h during the afternoon in exposed areas and along the coasts.

We are also in a period of Spring Tides. Storm Brendan will produce significant storm surges and the combination of these high Spring Tides, onshore storm force winds and storm surge will lead to a risk of flooding along all coasts. There is a significant risk to the south, west and northwest coasts with an elevated risk for all eastern coastal areas due to the high tides and the projected storm surge forecast.

The final figure displays the projected significant wave height for Monday evening. Offshore wave heights of up to 14 metres are forecast with high or very high seas forecast along all coastal waters. Met Éireann has issued a Status Red Marine warning for winds reaching violent storm force 11 in the west.

HARMONIE wind and warning isotach chart - Mon 06z

HARMONIE wind and warning isotach chart - Mon09z

HARMONIE wind and warning isotach chart - Mon12z

HARMONIE wind and warning isotach chart - Mon15z

HARMONIE wind and warning isotach chart - Mon18z

HARMONIE wind and warning isotach chart - Mon21z

ECMWF /Wave Ireland Significant wave height chart - Mon 18z

Please keep up to date at www.met.ie for warnings and forecasts for your area.

Heed the advice of the local authorities, the Gardaí and the HSE.

You can access our forecast products via these links:

https://www.met.ie/forecasts/atlantic-charts/precipitation-pressure

https://www.met.ie/forecasts/marine-inland-lakes/waves

At this link you can view the latest weather observations:

https://www.met.ie/latest-reports/observations

Issued by Harm Luijkx at 16:30 on Friday 10th January 2020

Unsettled spell of weather in the week beginning Monday 13th of January 2020

The weather will be very unsettled for the week to come with a sequence of developing depressions tracking across the Atlantic and affecting our weather.

Very windy weather is likely on Monday and possibly again on Tuesday and Thursday.

The forecast model from the European Centre forecasts that a depression, originating on the other side of the Atlantic, will deepen rapidly through Sunday and Monday as it tracks eastwards. The centre of the storm will move in the direction of Iceland and is expected to have a very low central pressure around 935 hPa on Monday night.

The strongest winds will stay to the northwest of Ireland, but there will still be a very strong wind field here as well, with the isobars close together over Ireland on Monday midday.

This chart from the UK Met office illustrates very well that the strong winds on Monday are expected ahead of the cold front.

The next system that will affect our weather can already be seen as a wave in the weather front to the southwest on the mid Atlantic. The pressure is not very low at that stage with 1003 hPa, but in the other charts above it can be seen that the expected pressure 12 hours later has come down to 988 hPa.

Because this system has not formed yet, the details of how it will affect us are uncertain at the moment of this writing (Friday afternoon, 10th of January).

Updated: 11am December 7th 2019 by Andrew Doran-Sherlock

Storm Atiyah (Ah-tee-ya) is forecast to track between Iceland and Ireland during Sunday producing strong winds and heavy rain from Saturday evening through to Monday morning.

• Status yellow winds will affect the country from Saturday evening through to Sunday morning and winds will increase further reaching orange level for Donegal, Galway, Leitrim, Mayo, Sligo, Clare, Cork, Kerry and Limerick. The yellow wind warning will continue for the rest of the country.

• A spell of heavy rain is forecast for all areas this evening (yellow rainfall warning for Donegal) and will be followed by squally heavy showers during Sunday.

This is the Met Éireann high resolution model, HARMONIE, with the forecast pressure and wind associated with Storm Atiyah. The colours indicate the warning levels.

Updated: 2pm December 5th 2019 by Liz Walsh

Met Éireann’s Forecast Office have been monitoring developments for Sunday the 8th December for a number of days now, and confidence is mounting for a period of potentially stormy weather for some parts of the country.

Widespread rain on Saturday night will clear eastwards overnight with a cooler, more showery westerly airflow following into Sunday. There is a threat of strong winds developing, accompanied by severe and squally gusts, chiefly in parts of the west and southwest, but the exact details as well as the timings are still open to change. Whatever the case, Sunday is shaping up to be a windy day countrywide with squally showers in the mix.

Below is an animation using data from the ECMWF of the surface pressure (solid black line), overlaid with the jet stream (in purple) and winds at 925hPa level (around 750 or 800 metres above the surface - sometimes used as an approximate indicator of gust speeds at the surface).

Met Éireann forecasters will continue to monitor the situation as we head into the weekend and warnings will be issued as required so stay tuned for further updates.

Updated: 5pm Thursday October 3rd 2019

Lorenzo has moved north-north-eastward parallel to the west coast of Ireland this afternoon as forecasted. The depression is still expected to take a turn eastwards this evening or early tonight whilst weakening. The latest forecast guidance has, however, slowed the eastward progression down. This means that we could see a more prolonged period of heavy rain in north-western parts of the country tonight and early tomorrow. Also, the timing and duration of the wind warnings have been and will continue to be adjusted accordingly - as required.

Storm Lorenzo was located around 180 nautical miles (340 km) west of Belmullet, Co Mayo at Midday today Thursday 3rd October 2019. The analysed pressure at 9z (1000 local) today was 969hPa at the M6 Buoy  which is located approximately 400 km west of Mace Head in Galway as the centre of the storm passed over, with storm force west to southwest gusts recorded on the southern side of the low pressure centre.

Our model guidance is calling for some slight deepening of the Lorenzo low to take place this afternoon as the system tracks north-eastwards to the west of Ireland, reaching a low of possibly 962hPa at 14z (1500 local). Because of this, south-easterly winds will be strong and gusty over much of the country this afternoon, with a countrywide yellow wind warning in operation until 6pm today.

The storm depression is forecasted to then turn east south-eastwards this evening towards the west coast of County Mayo (around 18z/1900local). This turn is due to upper air steering flows high up in the atmosphere. By this time, the depression will be starting to fill. What this means is that the storm force winds on the southern side of the low will begin to slowly subside. At 6pm, the orange level wind warning for western coastal counties of Galway, Mayo, Clare, Kerry and Limerick will come into operation, and the yellow wind warning will become confined to Sligo, Leitrim, Cork, Waterford, Tipperary and Wexford.

Below is some recent track guidance for the centre of Lorenzo from our HARMONIE Irish Regional Ensemble Prediction suite from midnight 3rd Oct to midday on 4th October.

For more information, please refer to our warning page on the website at www.met.ie/warnings

Hurricane Lorenzo in Climatological context

Hurricane Lorenzo is the eastern most and northern most category 5 hurricane ever recorded in the Atlantic Ocean. Hurricane Lorenzo is expected to make its transition from hurricane to extra-tropical storm when it is approximately at 49 degrees North, approximately 1000km to the southwest of Ireland. By comparison, storm Ophelia in October 2017 retained its hurricane status until it was within 500km of Ireland.

Met Éireann’s report on Storm Ophelia here

Met Éireann’s report on Storm Debbie here

Climate Change Context

The World Meteorological Organisation’s Task Team on Tropical Cyclones and Climate Change assessment has produced two reports on the Climate Change and Tropical Cyclones.  A summary can be found here: https://www.gfdl.noaa.gov/global-warming-and-hurricanes/

The main conclusion of the analysis are presented here:

Future Predictions:

• Sea level rise – which very likely has a substantial human contribution to the global mean observed rise according to IPCC AR5 – should be causing higher coastal inundation levels for tropical cyclones that do occur, all else assumed equal.
• Tropical cyclone rainfall rates will likely increase in the future due to anthropogenic warming and accompanying increase in atmospheric moisture content. Modelling studies on average project an increase on the order of 10 to 15 % for rainfall rates averaged within about 100 km of the storm for a 2°C global warming scenario.
• Tropical cyclone intensities globally will likely increase on average (by 1 to 10% according to model projections for a 2°C global warming). This change would imply an even larger percentage increase in the destructive potential per storm, assuming no reduction in storm size. Storm size responses to anthropogenic warming are uncertain.
• The global proportion of tropical cyclones that reach very intense (Category 4 and 5) levels will likely increase due to anthropogenic warming over the 21st century. There is less confidence in future projections of the global number of Category 4 and 5 storms, since most modelling studies project a decrease (or little change) in the global frequency of all tropical cyclones combined.

Past Observations:

• In terms of detection and attribution, much less is known about hurricane/tropical cyclone activity changes, compared to global temperature. In the northwest Pacific basin, there is emerging evidence for a detectable poleward shift in the latitude of maximum intensity of tropical cyclones, with a tentative link to anthropogenic warming.

• In the Atlantic, it is premature to conclude with high confidence that human activities–and particularly greenhouse gas emissions that cause global warming–have already had a detectable impact on hurricane activity.
• A recent study finds that the observed increase in an Atlantic hurricane rapid intensification metric (1982-2009) is highly unusual compared to one climate model’s simulation of internal multidecadal climate variability, and is consistent in sign with that model’s expected long-term response to anthropogenic forcing.
• Reduced aerosol forcing since the 1970s probably contributed to the increased Atlantic hurricane activity since then, but the amount of contribution, relative to natural variability, remains uncertain.
• There is some evidence for a slowing of tropical cyclone propagation speeds over the continental U.S. over the past century, but these observed changes have not yet been confidently linked to anthropogenic climate change.
• Human activities may have already caused other changes in tropical cyclone activity that are not yet detectable due to the small magnitude of these changes compared to estimated natural variability, or due to observational limitations.