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Climate Statement for September 2020

Warm first two thirds, cool final third. Wet in the Northwest, dry in the South

September 2020 started with low-pressure to the northwest, bringing active weather fronts across the country on Wednesday 2nd, with widespread heavy rain and some flooding in the Northwest. High pressure, which began to develop to the south of Ireland during the rest of the first week, gradually pushed the jet stream and low pressure systems further north, while keeping Ireland in a mild southwesterly airflow. This setup, which continued into the second week, brought a lot of dry weather, especially in the southern half of the country, but active weather fronts brought some heavy falls of rain to the North and North-west during this period. During the third week high pressure developed over mainland Europe and to the north of Ireland, which brought a warm and sunnier continental airflow over the country from the southeast and the dry conditions spread countrywide. The settled weather broke down at the beginning of the 4th week as a cold front brought a change of air mass with cooler conditions that continued for the rest of the month. The cold front was followed by an area of low-pressure crossing the south of the country on the 23rd and 24th, which brought widespread rain or showers. An area of high pressure gave a mostly dry final weekend of the month with plenty of sunshine, although cool at night with frost and fog in places. The month finished with active weather fronts moving in from the west on the 29th followed by heavy showers.

Rainfall: Below average for most
Nearly all rainfall totals were below their Long-Term Average (LTA) for the month. Monthly rainfall totals ranged from 41.6 mm (55% of its LTA) at Shannon Airport, Co Clare to 153.4 mm (117% of its LTA) at Newport, Co Mayo. Three stations in Co Cork had dry spells between Thursday 3rd and Monday 21st, including Moore Park, Cork Airport and Roches Point.

Temperature: Near or slightly above average overall
The majority of mean air temperatures were slightly above or slightly below their Long-Term Averages (LTA) for the month. Mean temperatures ranged from 12.0 °C (0.1°C above its LTA) at Knock Airport, Co Mayo to 14.2 °C (0.1°C be-low and 0.3 °C above their LTA respectively) at Sherkin Island, Co Cork and Roche’s Point, Co Cork.

Sunshine: Above average everywhere
All available sunshine totals were above their Long-Term Average. Monthly sunshine totals ranged from 109.8 hours (No LTA comparison*) at Belmullet, Co Mayo to 157.1 hours (No LTA comparison*) at Johnstown Castle, Co Wexford.

Wind: Strong gales reported
Monthly mean wind speeds ranged from 5.0 knots (9.3 km/h) at Moore Park, Co Cork to 14.5 knots (26.9 km/h) at Mace Head, Co Galway. The highest gust was 60 knots (111 km/h) reported at Valentia Observatory, Co Kerry while the month’s highest 10-minute mean wind speed was 44 knots (82 km/h) at Sherkin Island, Co Cork.

EXTREME VALUES AT SYNOPTIC STATIONS

Rainfall

  • Highest total: 153.4 mm at Newport, Co Mayo (117% of its LTA)
  • Lowest total: 41.6 mm at Shannon Airport, Co Clare (55% of its LTA)
  • Highest daily rainfall: 43.7 mm at Newport, Co Mayo (33% of its monthly LTA) on Wed 2nd

Temperature

  • Highest mean monthly temperature: 14.2°C at Shannon Airport, Co Clare (at its LTA), Sherkin Island, Co Cork (0.1°C below its LTA)
  • Roches Point, Co Cork (0.3°C above its LTA) and Valentia Observatory, Co Kerry (0.2°C above its LTA)
  • Lowest mean monthly temperature: 12.0°C at Knock Airport, Co Mayo (0.1°C above its LTA)
  • Highest Air temperature: 24.7°C at Phoenix Park, Co Dublin (7.0 °C above its LTA) on Mon 14th
  • Lowest air temperature: -2.1°C at Markree, Co Sligo (10.5 °C below its LTA) on Sat 26st (its lowest September minimum for 49 years)
  • Lowest grass minimum: -6.6°C at Oak Park, Co Carlow on Sun 27th (its lowest September grass minimum for 51 years)

Sunshine

  • Highest monthly total: 157.1 hrs (daily mean 5.24 hrs/day) at Johnstown Castle*, Co Wexford
  • Lowest monthly total: 109.8 hrs (daily mean 3.66 hrs/day) at Belmullet*, Co Mayo
  • Highest daily sunshine: 11.2 hours at both Gurteen*, Co Tipperary on Sun 20th and Belmullet*, Co Mayo on Sat 19th

Full report <<here>>

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