Meteorologist's Commentary

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

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, 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, 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 1pm Friday October 11th 2019 by Gavin Gallagher

Typhoon Hagibis is on track to make landfall in Japan on Saturday, October 12th. According to the Japan Meteorological Agency, this typhoon will be their most powerful storm of the year.

Visible Satellite of Typhoon Hagibis from 8am this morning (Irish time)

The centre of the storm is currently (1pm Friday) located 550 km south of the Japanese mainland and approx 750km south-southwest of Tokyo.

It currently has sustained winds of over 200km/h with gusts of 260km/h. This is equivalent to a Category Four hurricane in the North Atlantic.

Latest Track Map from the Japanese Meteorological Agency

It is forecasted that Hagibis will continue to track northwards then gradually turn towards the northeast this evening. Slow but steady weakening is anticipated during Saturday prior to landfall. Landfall is expected around 24 hours from now (10am Irish time, 6pm local Japanese time) with the current forecast bringing the centre of Hagibis passing close to the Tokyo area around 4pm Irish time Saturday, midnight local Japanese time.
Hagibis will then accelerate quickly out to sea to the east of Japan on Sunday.

Numerical weather forecasting model guidance remains in good agreement in terms of direction and speed and there is high confidence in the forecast track.
The Japanese Meteorological Agency has warned of strong winds, very heavy rain along with high waves and storm surge with coastal inundation.

Latest Warning Map from the Japanese Meteorological Agency

Relevant links:Japanese Meteorological Agency Warnings https://www.jma.go.jp/en/warn/index.html
Japanese Meteorological Agency Weather Forecast https://www.jma.go.jp/en/week/
Japanese Meteorological Agency Typhoon Information https://www.jma.go.jp/en/typh/
Joint Typhoon warning Centre https://www.metoc.navy.mil/jtwc/jtwc.html

Ireland play Samoa in the Rugby World Cup at 11:45am Saturday morning Irish time (7:45pm local Japanese time) in Fukuoka. Fukuoka is in the far southwest of the Japanese mainland and is not expected to be directly affected by Typhoon Hagibis.
The weather forecast for Ireland v Samoa on Saturday is dry and cloudy, it will be breezy with a temperature of 20°C.

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.