Thursday 13th August
Amber Warning of Extreme Heat issued at 10.01
N.B. The peak of 33.9C on Wednesday was exceed at 11.38 today, Thursday. The previous record of 34.1C set in 2020 was exceeded at 12.01.
The intense heat just built and built on Wednesday that resulted in a peak of 33.9C at 16.39 being a significant 12.3C above my long-term August average and 0.2C below my record for August set in 2020. The heat was slow to dissipate overnight that eventually produced a minimum of 16.9C at 05.37 being 5.1C above average, just before sunrise in Marlborough at 05.49. It was the hottest day since 9th July and the warmest might since 24th June.
As the partial eclipse reached its peak on Wednesday evening I observed that the pigeons, who frequent our roofs and who had fallen silent a little earlier, suddenly moved off together just after 19.00 and just before the peak of the partial eclipse. Previous to the start of the partial eclipse my records show that the solar radiation was falling steadily at a rate of about 30W/m2 every fifteen minutes. As soon as the eclipse started the solar radiation fell significantly at the rate of around 70W/m2 until about 19.00 when it began to tail off reaching a low at 19.30 before increasing again as the sun began to emerge from behind the earth’s shadow.
Thursday arrived with yet more strong sunshine that had lifted the temperature to 21.5C by 08.00, making it the warmest start to a day at that time since 11th July.
The soil temperature at a depth of 5cm, read daily at 08.00, already very warm after so many hot days, has continued to absorb more warmth during this heatwave with 20.9C, 21.6C and 24.2C recorded respectively over the past three days. I checked last night at 19.30, just as the extreme heat of the day was beginning to reduce, when the thermometer read 24.2C.
Often in the news it is commented when the temperature reaches 30C, well above the heatwave threshold for Wiltshire of 27C. Spending time indoors during the current heatwave I analysed my data to cover three five year periods for occasions when I recorded 30C or above. During the period of 2011-2015 there were just 5 days, from 2016-2020 there were 19 days and during the last five year period from 2021-2025 a significant increase to 28 occasions. This year there have already been 19 days when 30C or above has been recorded.
There were 3 days in September 2023 when 30C or above was recorded, a first for my station for September. Will that occur this year? A very clear picture of how the climate is heating up.
On Wednesday 30C was reached at 11.33, today, Thursday, 30C was reached at 10.14.
There are early signs that the heatwave will begin to ease after Friday and drop below the threshold by Saturday, when a cold front is forecast to slowly cross the country indicating a significant change into next week. Behind the cold front the Azores high will attempt to push a ridge back across the country although still dry on Saturday and Sunday. The wind will then come from a northwesterly direction, a cooler direction, that will result in lower temperatures by day. There has been a divergence of opinion over the last two days for the forecast from Monday, between the BBC and Met Office. As a gardener I hope the BBC is correct as they suggest we might receive light showers on Monday, although they only rate the possibility at 66% and even lower at 33% on Wednesday.