September has continued a quite impressive run of unusually warmer than average months for much of Western Europe and like June, pretty much all of Europe was warm. So much so this month could be one of Europe’s as well as UK & Ireland’s warmest September’s on record.
Warmth was one aspect, lack of appreciable rainfall another for southern and eastern UK while wetter, albeit close to average rainfall for much of Ireland and Scotland (mixed according to below % of normal past 30 days) but check out France and much of England! (See September Recap available next day or so for score!)
One possible reason behind this continued stuck pattern extending out of summer into autumn may well be a lack of tropical activity in Atlantic which often creates a ripple or kick to the atmosphere as well as feedback of warm sea/dry ground leading to higher pressure above. El Nino is likely another as it typically takes time for the jet stream to strengthen.
In the past 30 days most Atlantic fronts dropped most moisture on Ireland and Scotland thanks to strong euro ridging deflecting rain bearing Atlantic systems towards Norway and Iceland keeping much of England and France in the shadow and locked in it’s warm, sunny, dry cycle.
Despite some wetter weather sputtering south into the drought zone, conditions have worsened through September.
So the question is, will summer’s warm, dry curse continue for south and southeastern England and much of western mainland Europe into October and deeper into meteorological autumn? Or will it be a month which marks a fundamental super nino-induced switch in the form of strengthening Atlantic influence to more southern parts?
As cold gains ground over high latitudes and residual warmth lingers through the subtropics, the westerlies typically liven up with deeper lows. However both euro and gfs extended aren’t for great reading.
30-day MSLP anomaly
30-day precip anomaly
Both models unsurprisingly show generally warmer than average away from Scotland, SW Norway, Iceland.
When breaking down the 5-day increments 1-15th, note the GFS ensemble retrogrades the ridge but it’s dominant, perhaps triggered by Pacific tropical activity?
Therefore firmly drier than norm.
That westward pull back could mean cooler mid month like model suggests.
The CFSv2 weeklies are more fluid with the ridging towards mid month.
This suggests weaker ridge and potentially more open to Atlantic influence than GFS Ens suggests and that makes a big difference when it comes to rainfall.
As the below graphics show, past Super Nino’s have tended to see a transition from anticyclonic September/October followed by a shift to cyclonic and much wetter, albeit still mild November.
While timing a potential shift can be difficult, I believe this October ‘could’ see a shift to a more rigorous polar and possibly subtropical jet stream into Europe bringing a change to wetter, I suspect this, if it does come, would be towards the final 2 weeks.
The Verdict
A WARMER/DRIER than normal 1-15th with Atlantic lows clipping NW Ire/UK followed by potentially WETTER and more dominant Atlantic low pressure and possibly storminess (staying warmer than norm) between 15-31st for most of UK/Ireland/W Europe.
Overall near average temps & wetter NW Ireland, W/NW Scotland while Warmer, Drier E, SE Ire & most of England, Wales, E Scot into France, Wetter parts of Iberia and through Med. Most of Europe away from Scand, Iceland WARMER than average!
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