John Hammond’s Month Ahead – All sorts of Autumn!

The tropical Atlantic has been very quiet until recently; and within a few days, it will become relatively tranquil again. But briefly, the atmospheric lid has been lifted, allowing a number of hurricanes to erupt into life. These events may seem remote from us, but what effect might this explosion of energy have on our autumn? The atmosphere is a fluid – and the ripples can travel a long way… We’re in a for a rollercoaster ride.

 

Early warmth

Ex-Hurricane Helene brings stormy spell

Drier and chillier by the end of the month

 

 

MONDAY 17TH SEPTEMBER – SUNDAY 23RD SEPTEMBER

A ‘whirlwind’ week of weather

One things’s for sure – on our side of the ‘Pond’, we will not experience anything remotely as devastating as Hurricane Florence.

However, closer to home, ex-Hurricane Helene will be pivotal as it is swept up by the jet stream and catapulted towards us to start the week. There is an emerging consensus that this bundle of tropical energy will be impactful to the UK early in the week. But how impactful? There is still a large amount of disagreement between computer models, so it’s impossible to be too prescriptive at this stage. However, ahead of ‘Helene’, warm southerly winds may well briefly send temperatures into the mid-20s, most likely across eastern England early in the week. But storm clouds will be approaching and, on Tuesday, disruptive wind and rain look set to sweep rapidly across the west and north of the UK in particular. At this range, winds look more impactful than rain.

This will be a quick hit. By Wednesday, ‘Helene’ will be hurtling away from us. But after a brief respite, I expect a revved-up jet stream to propel one or two more wind and rain-makers in our direction in quick succession later in the week. Northwestern areas of the UK will be targeted, with the potential for further disruptive weather. A predominance of southwesterly winds will keep temperatures up though.

Then, towards the weekend, after a helter-skelter spell of weather, a marked change is on the way…

 

…the balance of power will shift towards higher pressure and drier weather

 

MONDAY 24TH SEPTEMBER – SUNDAY 30TH SEPTEMBER

Sudden change

The previous week’s hurricane hyperactivity may blow itself out, but it may leave a lingering imprint across the wider northern hemisphere, perturbing the North Atlantic jet stream into a much more meandering path of large loops. These big peaks and troughs tend to move more slowly, allowing near-stationary areas of high and low pressure to take up residence. The UK’s weather will depend crucially on exactly where they position themselves.

With time, the balance of power will shift towards higher pressure and drier weather. I expect a trend towards finer conditions through the week. With lighter winds than recently, days may feel pleasant; but if anything, temperatures will continue to ease down. There’s an increasing chance of night frosts and some lingering morning fog patches. And with the sun having headed south across the equator, there will be little argument that autumn is well and truly here.

 

MONDAY 1ST OCTOBER – SUNDAY 14TH OCTOBER

An eerie quiet… for a while

There are no really reliable signals from long-range models – certainly not that I trust, given recent performance. I wrote in the summer about the fitful nature of the jet stream and lack of sustained westerlies this year. And I expect the new month to continue this theme, allowing a quiet start to October. With shortening days and weakening sunshine, the air will have to come from a warm southerly source to keep temperatures up, and there’s no guarantee of that! Where winds fall light, frost and fog will become more of an issue with time. Rainfall will remain relatively infrequent, with disruptive storms less likely than at present.

Mists and mellow fruitfulness – the soft side to autumn But for how long? Should another burst of tropical cyclone activity erupt into life through October, this may again jolt the weather into a new frenetic phase later in the month.

And what of winter? My initial thoughts to come soon..

 

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