Good afternoon. I have been away on holiday for the past week so not had a chance to post any updates for a while.

Latest CET estimate for September is 15.77C. So a steady fall off for the rest of the month as would be expected. Temperatures should stay slightly above average until the final three days of the month, mainly due to mild nights. Final September CET could be very similar to August.

Despite the fall off in the CET in the second half of the month this could still be the 7th warmest September on record. The CET has reached 16C or more on 6 occasions in September. We have never had a 15.8C or 15.9C September.

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Chart 1

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Chart 2

Looking a little warmer now as the jet stream remains further north right through the weekend so should keep the CET area on the warm side of the jet until at least Sunday. Current CET estimate for September has now gone up to 15.99C.

Met Office Hadley     17.1c     Anomaly     3.1c provisional to 20th

Metcheck                  16.24c   Anomaly     2.54c

Netweather               17.05c   Anomaly     2.12c

Peasedown St John    16.40c   Anomaly   2.12c. 

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I got an estimate in the mid-16s from yesterday's GFS 12z, but the model has again failed to resolve the low minimum temps under the inversion this morning, so I think it would be more like low 16s now. Apply the typical downward adjustment from provisional Hadley CET onto that and you're at GW's latest estimate .

It sure has been an extraordinary month. Looks like it will join the three previous 2.0+ CET anomaly Septembers since 1950: 1999, 2006 and 2016.

Studying previous 1.5+ CET anomaly Septembers, a very warm North Atlantic was present in 7 out of 8 cases. 2021 has made it 8 out of 9. Unsurprising given that temps in the north-eastern N. Atlantic reach their peak during this month while dependence on sunshine diminishes and the impact of heat plumes does a bit too (though remains significant).

I now find myself wishing I'd put more stock behind that rather than what the models were showing for the opening third or so, as of the end of August! They saw the warm signal but were well down on its magnitude. To be fair, though, it was a truly exceptional spell of high temps that took place in the 2nd week.

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Met Office Hadley        17.0c      Anomaly       3.0c provisional to 21st

Metcheck                     16.15c    Anomaly       2.43c

Netweather                  16.93c    Anomaly       3.24c

Peasedown St John     16.4c     Anomaly      2.16c. 

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Met Office Hadley        17.0c      Anomaly       3.0c provisional to 21st

Metcheck                     16.15c    Anomaly       2.43c

Netweather                  16.93c    Anomaly       3.24c

Peasedown St John     16.4c     Anomaly      2.16c. 

Looks like we're going to slip below 17.0C

 

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Met Office Hadley      16.9c       Anomaly      2.9c provisional to 22nd

Metcheck                   16.12c      Anomaly       2.39c

Netweather                16.82c      Anomaly       3.13c

Peasedown St John   16.24c      Anomaly       1.96c.

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Met Office Hadley      16.9c       Anomaly      2.9c provisional to 22nd

Metcheck                   16.12c      Anomaly       2.39c

Netweather                16.82c      Anomaly       3.13c

Peasedown St John   16.24c      Anomaly       1.96c.

 

Can we stay above 16c , going to be very close

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16C+ in September is truly elite territory.
September 1999 was much feted for its warmth but fell short of this mark.
It also is looking more and more likely that we will finish above August which must be pretty rare (it did of course happen in the legendary 2006 which in many ways this years Aug/Sept combo has reminded me of)

Met Office Hadley        16.8c      Anomaly      3.0c provisional to 23rd

Metcheck                     16.07c    Anomaly      2.35c

Netweather                  16.77c    Anomaly      3.08c

Peasedown St John     16.2c     Anomaly       1.92c.  

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Looks like September could end up a full 6C warmer than May. Looking through the CET record the only time that has happened previously is 1729: May 10.3, September 16.6.

May this year was 10.1C so we need this month to end up 16.4C to equal, 16.5C to beat 1729. Unlikely, but should be clearly in second.

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A stunning month. 

20 of the 24 days have exceeded 20c.

The highest temperature during the whole of August here was 22.9c. We have exceeded that value 7 times this month with 2 days in excess of 29c.

Mean monthly temperature in August was 16.9c with 45mm rainfall

So far this month the mean stands at 17.5c with 2.8mm rainfall.

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Latest CET estimate still keeping just at 16C. It will be close. Monday still looks above average due to high overnight minimums as the cold front goes through. By Thursday the CET is looking very chilly. If it wasn't for the cold last couple of days we could have been around 16.2C.

Chart 1

Chart 2

Latest CET estimate still keeping just at 16C. It will be close. Monday still looks above average due to high overnight minimums as the cold front goes through. By Thursday the CET is looking very chilly. If it wasn't for the cold last couple of days we could have been around 16.2C.

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Chart 1

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Chart 2

 

All just about the margin that Weather Idle wins the month by 

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A stunning month. 

20 of the 24 days have exceeded 20c.

I agree it has been a stunning month 

However that's not going to prevent me from hitting the bottom after my guess & being late with penalties lol

 

Still all good fun though 

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A stunning month. 

20 of the 24 days have exceeded 20c.

The highest temperature during the whole of August here was 22.9c. We have exceeded that value 7 times this month with 2 days in excess of 29c.

Mean monthly temperature in August was 16.9c with 45mm rainfall

So far this month the mean stands at 17.5c with 2.8mm rainfall.

August really was crap wasn’t it. July wasn’t much better down here aside from one week. June was no great shakes. And May was awful. 

Forgettable summer somewhat salvaged by a nice September. 

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It would be hard for this to go sub 16 surely? Especially with the last few days relatively mathematically insignificant.

Interesting that with a few exceptions, the Had line and GWs are so parallel- and we know how accurate GWs estimates are towards the end of the month. Makes me think we shouldn't bother with the provisional HadCET data during the month- or take a fixed amount off. I still wonder why it's worth publishing them at all even as 'provisional'. 

Regarding this month, only the 1st and 2nd were sub 20 max here. I have only a few summer months in my records (back to 1860 fairly locally and the 1990s here) when 20C was exceeded on all days in the month and no Septembers. Obviously there will be some < 20 days in the cooler end-month spell but quite a month nonetheless.

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Interesting that with a few exceptions, the Had line and GWs are so parallel- and we know how accurate GWs estimates are towards the end of the month. Makes me think we shouldn't bother with the provisional HadCET data during the month- or take a fixed amount off. I still wonder why it's worth publishing them at all even as 'provisional'. 

The provisional CET data is a complete waste of time in my view as it is not accurate. The good news is that the Met Office is updating the CET data set soon with a fully traceable system. They have been promising this for a while so I won't hold my breathe. Their website has been saying the following since early this year:

"This version of CET will be superseded by CETv2 later in 2021. This will be a fully traceable system, with improved homogenisation and data adjustments to ensure a more consistent data-set through history and up to the present day. Further details to follow in due course."

 

The provisional CET data is a complete waste of time in my view as it is not accurate. The good news is that the Met Office is updating the CET data set soon with a fully traceable system. They have been promising this for a while so I won't hold my breathe. Their website has been saying the following since early this year:

"This version of CET will be superseded by CETv2 later in 2021. This will be a fully traceable system, with improved homogenisation and data adjustments to ensure a more consistent data-set through history and up to the present day. Further details to follow in due course."

That's the first I've heard of it and it does sound promising- exciting even. But then, I haven't felt your exasperation waiting for it!

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Met Office Hadley      16.8c      Anomaly      3.0c provisional to 24th

Metcheck                   16.15c    Anomaly      2.43c

Netweather                16.76c    Anomaly      3.07c

Peasedown St John   16.28c    Anomaly     2.0c.       

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Latest CET estimate still keeping just at 16C. It will be close. Monday still looks above average due to high overnight minimums as the cold front goes through. By Thursday the CET is looking very chilly. If it wasn't for the cold last couple of days we could have been around 16.2C.

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Chart 1

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Chart 2

I guess if September had 31 days and not 30 we'd be very likely to be under 16C?

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