Friday 1st September 2023

It’s the first day of autumn so of course it is time to talk about hot sunshine, at least partly thanks to Hurricane Franklin.

Thanks to Kathryn for the photograph.

Today starts cloudy with scattered heavy showers – an overhang of yesterday’s weather fronts. Gradually the cloud will break to allow for sunny spells, though also there will be a scattering of heavy showers breaking out once more. A tendency for the sun to be hazier later in the day too. Warm, we might squeeze 23’C. High cloud at first overnight, more in the way of low cloud and some mist/fog patches towards dawn. Down to around 14’C.

By Saturday we start to see the Azores High stretch up over the UK – helped along by Hurricane Franklin further to the west.

It will start cloudy, mist/fog patches in some places. Gradually it will burn away from around mid/late morning to leave sunny spells and fair-weather cloud for the rest of the day. A small chance of a shower. Warm, 23’C, maybe 24’C. Fairly clear skies for much of the night, though some low cloud and mist/fog patches developing by dawn. Down to around 11’C.

Sunday again starts with low cloud, mist/fog patches for most areas, but it will quickly lift into long sunny spells, with just a scattering of clouds and a bit of high cloud. Very warm, 25’C, maybe 26’C. Fairly clear skies overnight, some patches of low cloud/mist/fog forming by dawn, down to around 12’C.

By Monday our air source becomes France/Spain, so temperatures tick up. Early low cloud/mist/fog patches will quickly clear to long spells of sunshine. Quite hot, 27’C, maybe a shade more. Mostly clear skies overnight, down to around 13’C.

Tuesday sees long spells of sunshine, with a little high cloud at most. Fairly hot, around 27’C or so. Mostly clear skies for most of the night, but a chance of some patches of low cloud/mist/fog by dawn. Down to around 14’C.

By Wednesday we have pretty much the perfect set-up for heat – low pressure to the west of Spain/Portugal, high pressure to the east, a southerly breeze. Of course, it is September, the sun is weaker, the day is shorter – so the potential isn’t there for anything too hot. And our wet last two months have an impact too from the soil moisture profile and cooler seas around us.

So more sunshine for Wednesday, though perhaps a bit hazier than it has been with more in the way of high/mid-level cloud. Temperatures somewhere in the range of 27’C to 30’C. A warmer night probable, due to the high/mid-level cloud, say around 17’C.

Thursday probably keeps the hot conditions, with high/mid-level cloud making it hazy. Temperatures more likely in the range of 28’C to 32’C. An outside chance of a shower. A warm night probable.

Confidence reduces by Friday, as is fairly usual a week away, but the more likely outcome keeps the hot sunny weather, with temperatures in the range of 27’C to 31’C.

So at some point I’d expect an attempt at a breakdown, whether that be a westerly flow, or thundery showers moving up from the south/south-west, maybe Friday, maybe over the weekend or maybe not until early next week. I’d possibly pin Sunday as the more likely day in a fairly broad range.

Until the breakdown, it will be hot with sunny spells, perhaps hazy. After the breakdown there’s still a fair chance that it will settle down again and remain warm with sunshine at times. But, hurricanes in the western Atlantic can change plans…so always take September mid-range forecasts with even more of a pinch of salt than usual.

Enjoy your weekend, I’ll try to do the autumn forecast during it.

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