The provisional mid-month statistics for September are in and clearly show the unseasonably warm weather the UK has been experiencing.
In the first half of September the UK was on average warmer than June, July and August with a mean temperature of 15.9°C, 3.3°C higher than the average September. Norfolk and Suffolk have seen the biggest variance from the average with temperatures so far 4.3°C over the September average.
The hottest day of the year was recorded in Gravesend on 13 September at 34.4°C, the last time the hottest day was in the month of September was in 1954 and recorded at Regents Park. The last time there were three consecutive days above 30°C in September was 1929.
Minimum temperatures were also significantly higher than average. The minimum temperatures in North West England and Eastern Scotland were 3.8°C warmer than average.
These higher temperatures both through the day and night have been caused by warm and humid air being drawn up from the Continent. The map below clearly shows the increased average maximum temperatures across the UK in September so far.
|Max temp (°C)||Min temp (°C)||Mean temp (°C)|
|1-14 September 2016||Act||Diff from avg (8110)||Act||Anom (8110)||Act||Anom (8110)|
Although unseasonably warm, there have also been some wet conditions across the UK. Northern Ireland has had 71% of its average rainfall for the month, with County Fermanagh already surpassing the expected average with 101.8mm of rain so far this month. Some of this rainfall has been intense causing some surface water flooding. The early hours of 16 September saw Swanage in Dorset receive 31.8 mm and Cavendish in Suffolk 22.2 mm of rain in an hour.
|1-14 September 2016||Act||% of avg (8110)|
We are expecting a return to more usual September weather across the UK with temperatures reducing and frontal systems coming in from the Atlantic. We expect to see a continuation of the North West/South East split through the second half of the month, with the wettest and windiest conditions in the North West and drier and brighter weather in the South East with some rainfall as you would expect for the time of year.
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“These higher temperatures both through the day and night have been caused by warm and humid air being drawn up from the Continent.”
If that statement were strictly true, why do the temperature anomalies increase longitudinally from west to east along the south coast?
I would have thought that as the warm air was drawn up from the Continent the temperature anomalies would be aligned latitudinally rather than longitudinally even allowing for the extra sea track, but the anomalies in the SW are as low as anywhere in the country.
For whart its worth that temperature anomaly chart looks to me like one produced by more of a tropical maritime flow in a period of SW’lys when its cloudy and muggy in the SW, and warm or even hot in the sheltered and sunnier east.
As far as I remember there was air caught up in extratropical lows from a couple of ex tropical storms or depressions during the first week of September that brought extremely warm and humid air with greater than 570 dam (1000-500 hPa) thicknesses across the country.
I’ve had a closer look at the weather types for the first 14 days of September by downloading the Lamb Weather Types for each day from the Climate Research Unit of the University of East Anglia. Please excuse the abbreviations but most are self explanatory (U = unclassified; A = Anticyclonic)
01 : SW
02 : W
03 : SW
04 : U
05 : SW
06 : ASW
07 : S
08 : SW
09 : SW
10 : ASW
11 : S
12 : SW
13 : U
14 : E
I realise that the surface flow is backed by around 30° from the gradient, but the tropical air that caused the warm start to September was primarily maritime in origin and not continental. Air from the continent will always be drier and less humid than tropical maritime air is.
I made the first comment on Saturday morning, it’s now Thursday afternoon, have you forgotten me again or was it something that I said?
It’s been a week and I got fed up waiting…
Just discovered these comments.
I had the same experience when posting a comment at Channel 4 Weather recently.
My guess is that the shorter sea track into south east England (even when the wind is S or SSW) plays a key role (and despite Cornwall being somewhat further south than Kent).