We are now in a very different type of pattern compared to what we were last month and the change as alluded to and expected since way back in mid-July was due to the sharp rise in water temperatures surrounding the UK along with the progression of the season and the cooling which was taking place up at 500mb just to our north. This change allowed heights to lower and thus our pattern was seen to turn more unsettled and that indeed turn out correct.

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I believe we will have a warm-up on the way, perhaps at the close of August and start to September and the evidence is in the fact that the NAO is set to go sharply positive. September could start off very nice across western Europe but it may be cool and unsettled further east into central and eastern areas while the Med stays above normal.

Here’s the GFS NAO ensemble which shows the return to positive.

The CFSv2 500mb heights show a strong ridge positioned just north of Scotland week 3 or between Aug 25-Sept 1 but as you can see, the heights significantly lower once again by week 4 which is no surprise given that the increase in cool to the north of the UK and those warm waters will do their dirty work once again. The warm up is likely to be short lived I think but it may start September on a good note and one that leads people into a false sense of security. The majority of the month looks much like August with unsettled conditions but with spells of warmth and settled conditions in between. My concern is that we get a spell of very wet weather late month and also a sharp cool down with early frosts thanks to cold building early and a negative NAO and AO.

The below CFS chart shows average temperatures for the UK and Ireland, but below normal to the south over France and Iberia while to the east it’s above normal over the Low Countries, Denmark and Scandinavia where warm high pressure settles. Eastern Europe should see a warmer than normal month.

Below is the current sea surface temperatures and this profile suggests that with lower heights as we head deeper into autumn, may support a lot of wet conditions towards mid and late month with flooding a real possibility. Back in September 2009 with a similar ENSO and water temperature profile, we some record rains followed by a drier October which then was followed by a very wet November.

Here’s the precipitation forecast according to the CFS.

All in all, September may start warmer than normal but we should see a largely mixed bag much like this month but the concern is very much on a potential 10-15 day wet spell which could cause flooding rains.

I intend to have my European autumn (Sept through Nov) forecast up later this week.

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Tags: Europe Autumn forecast 2013