This post is on the late September/early October 2011 "heatwave" in Ireland and the UK.
What happened was that an intense high pressure sat to the southeast of the UK with low pressure just out to the west of Ireland drawing in a long fetched southerly to southwesterly airflow. The air was coming all the way from the Canary Islands and Iberia. How this came to fruition was through a warm front that pushed northwards on the 26th September after bringing heavy rain widely on the 25th. This eventually turned to cloud but more rain started to approach from the Atlantic into the west of Ireland and Scotland overnight on the 27th. This brought much cloudier and cooler conditions with temperatures failing to reach 20°C. However, the east of Ireland, England and Wales were all under clear air. At this time of year, the sun is still very strong so only made the temperatures shoot up on the 27th, 28th and the 29th before the rain reached the east of Ireland on the 30th and brought some flooding crashing with the warmth which only led to the rainfall intensifying. Oak Park had a daily rainfall of 48.1mm on September 30th.
This period had several of the warmest days of the entirety of 2011. Summer 2011 was very cool and is the coolest Summer of the 21st century so far - the Summer months and January were the only cool months in 2011. Phoenix Park had a maximum of 25.7°C on September 28th, its highest for September since 1906 and in fact, this was the station's warmest day of the year, warmer than any day during Summer 2011. Dublin Airport had 24.1°C whilst Casement Aerodrome had 24.4°C both on the same day, their highest September temperatures since 2003. This combined with abundant sunshine in them places made for some very pleasant weather to be had. I remember going to the beach after school to enjoy it because it was very unusual to see such warmth in September and especially for how late in the month it was. We didn't have to wait all that long to find such unusual warmth again in September 'cause 2016 did so.
Two new September date records were set for temperature in the UK with maxima of 28.8°C on the 29th and 29.2°C on the 30th. Two new October date records were set for temperature in the UK with maxima of 29.9°C on the 1st and 29.3°C on the 2nd with the 3rd being equalled for its highest maxima of all-time of 28.3°C (1908 and 1959 were the other years that recorded this on October 3rd). The maxima of 29.9°C on 1st October 2011 became the highest October temperature on record in the UK and just 0.1°C short of 30°C. The previous record was 29.4°C on 1st October 1985.
Rainfall was persistent on 1st October 2011 in the east of Ireland leading to further flooding, particularly in the Dublin area with the county having more than half of its October monthly rainfall on this day already (don't forget there was even more severe rainfall to come on the 24th October a few weeks after). Dublin Airport had a daily rainfall of 44.8mm on this day whilst Casement Aerodrome and Phoenix Park had 27.3mm and 35.4mm respectively.
The rain dissipated on the 2nd October generally but still lingering in northern England. More rain but mainly light pushed into the north on the 3rd with warmer temperatures across Ireland but England and Wales bit down on preceding days though still continuing very warm. Ashford, Co. Wicklow had 21.4°C on this day. It wasn't very sunny though in the warmth (bar England and Wales), it was mainly cloudy.
MODIS satellite for 1st October 2011.
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