July 2019 saw the month’s daily maximum record broken on the 25th with a high of 36.8C, The reading beat the previous record set on July 1st 2015 by 0.8C and was the second highest reading recorded in this area. Cloud that drifted in mid afternoon put paid to any chance of all-time record though Cambridge, further north, managed to break the UK record with a reading of 38.7C. This temperature set in the Botanic Gardens beat the previous record of 38.5C set in Brogdale, Kent, in 2003.
Although it has been mentioned that the Cambridge site appears to be overdeveloped it meets the WMO standard and the Met Office are happy with the record.
Compared with 2003 the heat this time was far more widespread and further north, with many stations recording higher values than 2003, as shown by these 24 hours to 6pm readings below.
In 2003 some 44 stations recorded 30C or above whereas this year some 67 reached 30C or higher.
Though the heat was record breaking it was much shorter lived than 2003. Like last month and July 2015 the 9-day temperature trace is far more ‘pointed’ – perhaps a symptom of the changing behaviour of the jet stream.
Overall the monthly mean finished 19.9C, that’s 1.4C above average though 1.8C cooler than last July – the warmest month on record.
Rainfall at 61.5mm, was 141 per cent of average, the wettest for 2 years. Sunshine, at 165hrs, is 85 per cent of average and well down on last July’s 273hrs.
The month can also throw up some striking anomalies, none more so than the fact that the 13th is the only day in the month where the temperature has ever reached or exceeded 30C anywhere in the British Isles.
According to TORRO the highest daily maximum recorded in the UK is 28.3C at Earls Colne, Essex, in 1948; at Brixton, south London, in 1896 and Aboyne in 1994. Yet either side of this date has records comfortably above 31C, as the table below shows.
The closest we’ve got locally to 30C in the last 60 years was in 1989 when 27C was recorded.
So why is the 13th ‘cursed’ with traditionally being the coolest day of the month? The best explaination perhaps is the fact that the date occurs more or less during the middle of the North-west European monsoon.
According to Philip Eden’s list of singularities the June monsoon can strike any time between the 1st and 21st but normally peaks on the 16th with a 77 per cent frequency.
As well as cool temperatures the phenomenon can also bring copious amounts of rain, as happened in 1903 when large parts of Redbridge were inundated following a 59-hour deluge that started on… the 13th.
Will we see a repeat this Thursday? Unlikely, though the general pattern is not that different to what led to events over a hundred years ago.
Since February most of this region’s rainfall has been falling during the first half of the month.
May (to 26th) 54%
With only one of these months wetter than average the long-term, rolling trend continues to head downwards.
Considering past rainfall patterns it can only be a matter of time before the graph heads upwards again. Looking further back at rainfall data to 1961 reveals the extremes were higher and that the jump from dry to wet can be sudden.
The wettest 12-month rolling period ended mid way through May 1975 with a total of 873mm. However, just 16 months later, at the end of the hot summer of 1976, the rolling 12-month average was just 302mm, that’s less than half of our average annual rainfall!
April 2019 was yet another dry month. Just under 12mm was recorded, that’s 28 per cent of average.
There has been rain around but the prevailing wind has not been conducive for great amounts to fall here. Last weekend, over a period of 5 days, just 0.9mm fall. Yet Capel Curig in Snowdonia, 200 miles northwest as the crow flies, recorded 130mm thanks to a NW’ly regime.
A look at rainfall in Wanstead back to July 2013 shows that of the 3,550mm recorded just 17 per cent has fallen when the wind was NW’ly.
Because of the topography of the area most of our rain falls when the wind is blowing between SE’ly and SW’ly, a total of 43 per cent.
A westerly is usually reliable for rainfall, however because this area is in the lee of high ground areas such as Hampstead westerlies have delivered just under 8 per cent of that 6-year total.