August was warm, wet and unusually stormy
August 2020 was warm, humid and cloudy with two named storms in the final third of the month. The first week saw a mostly west or south-westerly airflow with high pressure to the south and low pressure to the north bringing bands of rain or showers, especially between the 3th and 5th. The second week saw a slack, mostly easterly airflow over the country, with high pressure to the northeast over Scandinavia. This brought a few dry, sunny days, but as the week wore on, heavy thundery pulses of rain pushed up from the southeast to affect the southern half of the country, especially on the 13th and 15th. Atlantic low-pressure systems dominated most of the remainder of the month with coastal, river and flash flooding causing disruption in some areas. Slow moving weather fronts gave heavy falls of rain in places on the 17th and 18th before Storm Ellen, a record breaking deep Atlantic low pressure system, which contained the remnants of Tropical Storm Kyle, brought wide-spread gales and heavy rain or showers, sometimes thundery, across the country between the 19th and 21st. After a brief respite, another deep Atlantic low-pressure system, Storm Francis, brought very heavy falls of rain and gales across the country late on the 24th and into the 25th. Yet another Atlantic low-pressure system brought more bands of rain or showers, sometimes thundery on the 27th and 28th before a cool North Atlantic high-pressure system settled it down for the final few days of the month.
Rainfall: Above average nearly everywhere
The majority of monthly rainfall totals were above their Long-Term Average (LTA). Percentage of rainfall values ranged from 95% (monthly rainfall total of 100.1 mm) at Finner, Co Donegal to 215% (monthly rainfall total of 189.7 mm) at Sherkin Island, Co Cork (its wettest August since 1986). Monthly rainfall totals ranged from 85.1 mm (118% of its LTA) at Casement Aerodrome, Co Dublin to 219.7 mm (191% of its LTA) at Valentia Observatory, Co Kerry (its wettest August since 2009). The month’s wettest day was also recorded at Valentia Observatory, Co Kerry with 52.0 mm on Mon 24th (its wettest August day since 1986).
Nearly all mean air temperatures were above their Long-Term Average (LTA) for August. Deviations from mean air temperature ranged from -0.5 °C (14.7 °C mean temperature) at Dublin Airport, Co Dublin to 0.9 °C (the month’s lowest mean temperature of 14.6 °C) at Knock Airport, Co Mayo (its warmest August since 2003). Mean temperatures were as much as 16.4 °C (0.3 °C above its LTA) at Shannon Airport, Co Clare (its warmest August since 2003). The month’s highest temperature was reported at both Markree, Co Sligo and Mount Dillon, Co Roscommon on Friday 14th and Saturday 15th with a temperature of 25.2 °C.
EXTREME VALUES AT SYNOPTIC STATIONS
Rainfall
- Highest total: 219.7 mm at Valentia Observatory, Co Kerry (191% of its LTA) (its wettest August since 2009)
- Lowest total: 85.1 mm at Casement Aerodrome, Co Dublin (118% of its LTA)
- Highest daily rainfall: 52.0 mm at Valentia Observatory, Co Kerry (45% of its monthly LTA) on Mon 24th (its wettest August day since 1986)
Temperature
- Highest mean monthly temperature: 16.4°C at Shannon Airport, Co Clare (0.3°C above its LTA) (its warmest August since 2003)
- Lowest mean monthly temperature: 14.6°C at both Knock Airport, Co Mayo (0.9°C above its LTA) (its warmest August since 2003)
- Highest Air temperature: 25.2°C at both Markree, Co Sligo on Fri 14th and Mount Dillon, Co Roscommon on Sat 15th
- Lowest air temperature: 1.6°C at Mount Dillon, Co Roscommon on Mon 31st
- Lowest grass minimum: -1.4°C at Mount Dillon, Co Roscommon on Mon 31st
Sunshine
- Highest monthly total: 151.5 hrs (daily mean 4.89 hrs/day) at Cork Airport, Co Cork
- Lowest monthly total: 97.2 hrs (daily mean 3.14 hrs/day) at Dublin Airport*, Co Dublin (its dullest August on record (length 78 years))
- Highest daily sunshine: 14.5 hours at Malin Head*, Co Donegal on Sat 8th
Full report <<here>>
Summer was wet and dull with a stormy finish
After a spring where a weakened Jetstream remained away from Ireland to the north or south, the summer of 2020 saw an unseasonally strong North Atlantic Jetstream dominating our weather, keeping it mostly unsettled and cool at times. From a relatively dry beginning, June saw two intense thunderstorm outbreaks, between the 13th and 16th and on the 25th and 26th, when warm humid air was drawn up from the southeast over the country. The Jetstream was most active near Ireland in the final third of the month with Atlantic low-pressure systems bringing rain or showers on most days. July saw the Azores High briefly pushing up over Ireland between the 9th and 11th and between the 19th and 21st but for most of the month Ireland was situated directly under, or on the northern side of the Jetstream, keeping it cool and wet with low pressure in charge. The Jetstream weakened for a while after the first week of August, which brought some dry pleasant days, but slow moving fronts and thundery continental low-pressure systems kept it mostly cloudy with heavy rain at times. The final third of August saw the Jetstream activate again in the Atlantic, which brought two named storms, Storm Ellen and Storm Francis over the country with widespread gales and heavy rain causing some flooding.
Rainfall: Above average everywhere
All rainfall totals were above their Long-Term Average (LTA) for the season. Percentage of rainfall values ranged from 113% (the lowest seasonal rainfall total of 217.1 mm) at Oak Park, Co Carlow to 181% (the highest seasonal rainfall total of 561.1 mm) at Valentia Observatory, Co Kerry (its wettest summer since 2009). The season’s wettest day was also recorded at Valentia Observatory, Co Kerry with 54.5 mm on Wednesday 29th July
Temperature: Below average in most places
The majority of mean air temperatures across the country were below their Long-Term Average (LTA) for the season. Mean temperatures were lowest at Knock Airport, Co Mayo with 13.2 °C (0.1 °C below its LTA). The season’s highest temperature was reported on the first day of summer (Monday 1st June) at Newport, Co Mayo with a temperature of 27.1 °C.
Sunshine: Below average everywhere, dullest summer on record for Dublin Airport
All available monthly sunshine totals were below their Long-Term Average (LTA) for the season. Percentage of seasonal sunshine values ranged from 78% (seasonal sunshine total of 361.2 hours) at Casement Aerodrome, Co Dublin (its dullest summer since 1987) to 89% (the season’s highest seasonal sunshine total of 451.2 hours) at Cork Airport, Co Cork. Seasonal sunshine totals were lowest at Gurteen, Co Tipperary with 275.5 hours (No LTA comparison*). The highest number of daily sunshine hours recorded this season was on the first day of summer (Monday 1st June) with 15.6 hours at Johnstown Castle, Co Wexford.
Wind: Gales, strong gales and storm force winds reported with two named storms
Seasonal mean wind speeds ranged from 5.5 knots (10.2 km/h) at Ballyhaise, Co Cavan to 12.9 knots (23.9 km/h) at Mace Head, Co Galway. Gales were reported on 5 days or more during the season with strong gales reported on Thursday 20th August during Storm Ellen and Tuesday 25th August during Storm Francis. Mean wind speeds were storm force and reached violent storm force 11 on the south coast on Wednesday 19th August during Storm Ellen.
EXTREME VALUES FOR SUMMER AT SYNOPTIC STATIONS
Rainfall:
- Highest seasonal total: 561.1 mm at Valentia Observatory, Co Kerry (181% of its LTA)
- Lowest seasonal total: 217.1 mm at Oak Park, Co Carlow (113% of its LTA)
- Highest daily rainfall: 54.5 mm at Valentia Observatory, Co Kerry (55% of its monthly LTA) on Wed 29th Jul
Temperature:
- Highest mean seasonal temperature: 15.2°C at Oak Park, Co Carlow (0.3°C above its LTA)
- Highest mean seasonal temperature: 15.2°C at Oak Park, Co Carlow (0.3°C above its LTA)
- Highest air temperature for the season: 27.1°C at Newport, Co Mayo on Mon 1st Jun
- Lowest air temperature for the season: 1.6°C at Mount Dillon, Co Roscommon on Mon 31st Aug
- Lowest grass minimum for the season: -1.6°C at Mount Dillon, Co Roscommon on Mon 8th Jun
Sunshine
- Highest seasonal total: 451.2 hrs (daily mean 4.90 hrs/day) at Cork Airport, Co Cork
- Lowest seasonal total: 275.5 hrs (daily mean 2.99 hrs/day) at Gurteen*, Co Tipperary
- Highest daily sunshine for the season: 15.6 hours at Johnstown Castle*, Co Wexford on Mon 1st Jun
Full report <<here>>