September 2023 C.E.T. and EWP forecast contests

[Scorcher]

It begs the question as well...will this even be the last of the heat we see in September?

I would not be surprised to see another hot spell before the end of the month now (although not on this level).

[Don]

1 minute ago, Scorcher said:

It begs the question as well...will this even be the last of the heat we see in September?

I would not be surprised to see another hot spell before the end of the month now (although not on this level).

Wouldn't be surprised to see at least another settled spell.  Question is, will it be hot or more pleasantly warm by day and cool at night?

[SqueakheartLW]

An extraordinary start to September here and having 5 of the 8 days so far with CET means above 20C as well

We are now pulling well clear of any of the Septembers that went on to finish as a top 10 September on the CET mean and I expect the CET mean for today to come in above 20C as well and will very likely be the last one that does but tomorrow could be a close call for this. After that sub 20C looks certain.

[Don]

5 minutes ago, SqueakheartLW said:

An extraordinary start to September here and having 5 of the 8 days so far with CET means above 20C as well

We are now pulling well clear of any of the Septembers that went on to finish as a top 10 September on the CET mean and I expect the CET mean for today to come in above 20C as well and will very likely be the last one that does but tomorrow could be a close call for this. After that sub 20C looks certain.

I wonder where the CET will be in a week, Mid-17's?!  Still very warm.

[Scorcher]

50 minutes ago, SqueakheartLW said:

An extraordinary start to September here and having 5 of the 8 days so far with CET means above 20C as well

We are now pulling well clear of any of the Septembers that went on to finish as a top 10 September on the CET mean and I expect the CET mean for today to come in above 20C as well and will very likely be the last one that does but tomorrow could be a close call for this. After that sub 20C looks certain.

Tomorrow must have a good chance as well as tonight/tomorrow night are looking very warm. If the minimum ends up around 17C it won't take a particularly hot day to take the mean over 20C for the day.

[The PIT]

Sunny Sheffield up to 20.2C, +4.1C above normal. Rainfall 1mm 1.5% of the monthly rainfall.

May get another rise today and then thankfully downwards probably for the rest of the month.

Edited September 10, 2023 by The PIT

[Derecho]

The long range output is extremely uncertain, with plenty of members suggesting some warmer air moves in next weekend as low pressure stalls out west. Others bringing in a cool north-westerly and then loads of other options amongst ensemble members....

Until we know what tropical Margot will do its difficult to predict where the CET will go. The 00z GFS is one of the cooler runs for next weekend with the CET projected to go as follows:

10th: 20.4 (20.8 - note the thundery conditions have dented this daily mean for today a lot)
11th: 20.2 (17.6)
12th: 19.8 (14.4)
13th: 19.3 (15.3)
14th: 19.1 (16.4)
15th: 18.7 (12.5)
16th: 18.3 (11.6)
17th: 17.9 (12.4)
18th: 17.5 (11.4)
19th: 17.1 (9.9)
20th: 16.8 (10.8)
21st: 16.5 (10.8)
22nd: 16.5 (14.8)
23rd: 16.4 (14.3)
24th: 16.3 (15.5)
25th: 16.3 (15.9)
 
Better off throwing in a random number generator for the CET returns after this coming week though. If we get warmth drawn up from the south next weekend instead we have a chance of the warmest September CET on record. If the above scenario played out we'd need an exceptional end to the month to lift the CET back up.

[Earthshine]

The rolling mean CET up to the 9th for July 2018 and September 2023:

July 2018: 20.1°C

September 2023: 20.3°C

The mean maximum CET is an absolutely ludicrous 26.5°C, 9.0°C above the 1961-1990 mean.  Absolutely INSANE!  This has got to be by far the hottest start of any September.

[Stationary Front]

Have there been many first 10 days of July warmer than this September? 

[Earthshine]

2 minutes ago, Stationary Front said:

Have there been many first 10 days of July warmer than this September? 

I think 1976 was more anomalous, particularly for maximum CET.

[Methuselah]

2 minutes ago, Earthshine said:

I think 1976 was more anomalous, particularly for maximum CET.

Even more so given the 1961-90 mean? But 1976 is still the deniers' first port of call when denying the obvious reality of AGW. Just how hot were the first ten days of July 1976? 

[Earthshine]

3 minutes ago, Methuselah said:

Even more so given the 1961-90 mean? But 1976 is still the deniers' first port of call when denying the obvious reality of AGW. Just how hot were the first ten days of July 1976? 

First 9 days of July 1976 had a pretty bonkers mean CET of 22.7°C by my calculations, around 6.8°C above normal.  First 9 days of September 2023 are 6.7°C so this is the July 1976 of Septembers, at least in terms of the first third.  Mean max was about 30.3°C up to the 9th so July 1976 was actually more anomalous than this month up to the 9th.

[Summer Sun]

20.3c to the 9th

6.7c above the 61 to 90 average
5.3c above the 81 to 10 average

[richie3846]

2 hours ago, Methuselah said:

Even more so given the 1961-90 mean? But 1976 is still the deniers' first port of call when denying the obvious reality of AGW. Just how hot were the first ten days of July 1976? 

I question if it's fair to put people into a black and white category, such as 'denier'. There were some significant September heatwaves in the late 19th and early 20th century. This one was not very different from those heatwaves in terms of the temperatures achieved. What's different about this one is the length, but is that solely down to the synoptics? The position of the high was very favourable for ideal winds to arrive from warm places. Given the fact that the top temperatures were not in excess of the heatwaves of Septembers yesteryear, can this genuinely be put down to climate change? Is it right to box people off as deniers, if they question the nature of this particular heatwave?

The Met Office have already said they will do an attribution study on this particular heatwave. My gut instincts suggest this particular heatwave is not overly influenced by climate change, and more about the specific wind directions we've experienced this past week. In other words, it may have happened anyway. 

Edited September 10, 2023 by richie3846

[Dancerwithwings]

The last seven days have blown my 15.4c guess out of the water, unless the last week of September gives us a full on northerly…I haven’t a hells bells chance

Edited September 10, 2023 by Dancerwithwings

[SqueakheartLW]

1 hour ago, Dancerwithwings said:

The last seven days have blown my 15.4c guess out of the water, unless the last week of September gives us a full on northerly…I haven’t a hells bells chance

I think we'll struggle now to get anything below 16C by the end of the month. A good guess if we go back to around average would be around 16.5C meaning 2006 should be safe but if we get another warmer spell then 2006 looks in danger of falling.

Also what are the chances we get a 17C September or even beat June 2023 to set the warmest month of the year in September. That can't happen very often, especially after average or above average summer months before it.

GFS 00z Model runs to predict possible rolling September CET

Using these three 2m temp runs I will create 3 possible scenarios of how September could play out up to the 25th. The 2m temp mean, P05 and P06.

Average

Using the 2m temp mean we get the following out to the 25th September

Still a very respectable 17.188C by the 25th if the GFS 00z 2m temp mean plays out as shown here. The yellow numbers are provisional CET values and the green for average values are in for the 10th to 25th. This puts us very close to 2006 at this stage with 2023 only a small margin warmer but looking like we'll drop below it before the end of the month.

Coldest member - P05

How will September 2023 possibly pan out if we go cooler than predicted and follow a route similar to P05? The result is below.

With using the coldest P05 member and colour coding these figures blue for cold we can see what a difference this makes to the rolling September CET with a value at 15.924C by the 25th. Still a warm value for September but at least not so ridiculous. This also places us below 8 of the top 10 years by this stage with only 1895 and 1929 still provisionally below 2023 if this coldest run were to prove the correct one.

Warmest member - P06

Now how ridiculously warm could September 2023 look if we do something similar to what is showing in P06?. The result is below.

With using the warmest P06 member and colour coding these figures red for warm we can see how ridiculously warm September 2023 could possibly turn out if we do indeed bring in another warm or very warm spell later in the month. This particular run leaves a provisional rolling September 2023 CET of a whopping 18.248C by the 25th which would effectively guarantee the 2006 record is smashed by a country mile and would possibly not only guarantee at least a 17C September but would be threatening a 18C September. This would be the December 2015 equivalent of a September month if this were to come off.

[Frigid]

GFS 12z looks very cool, could see the CET dip below 16C if it all comes to fruition. Of course I expect a middle ground, 16C is definitely looking likely. 

[Scorcher]

37 minutes ago, Frigid said:

GFS 12z looks very cool, could see the CET dip below 16C if it all comes to fruition. Of course I expect a middle ground, 16C is definitely looking likely. 

Far too early to make those sorts of assertions. The ECM actually looks pretty warm towards the end of the week.

I also think to go below 16C we would need a cooler high pressure with chilly nights (which doesn't look like happening at the moment). A trough over the UK probably wouldn't be that cool overall due to the cloud cover at night. 

Edited September 10, 2023 by Scorcher

[Derecho]

31 minutes ago, Frigid said:

GFS 12z looks very cool, could see the CET dip below 16C if it all comes to fruition. Of course I expect a middle ground, 16C is definitely looking likely. 

Still has a CET of 16.2C to the 25th.

One thing to note is that quite a few model runs are developing lower heights to our west later this week which would bring some warm air back up from the south for a few days. If that happened a record breaking September CET is possible. 

CET is likely to be around 18.5C by the 16th, cooler weather for the middle of this week has been downgraded.

[Don]

30 minutes ago, Derecho said:

Still has a CET of 16.2C to the 25th.

One thing to note is that quite a few model runs are developing lower heights to our west later this week which would bring some warm air back up from the south for a few days. If that happened a record breaking September CET is possible. 

CET is likely to be around 18.5C by the 16th, cooler weather for the middle of this week has been downgraded.

Typical! 

[summer blizzard]

The key target is 15.6C for the top 10.

[Derecho]

The GFS this morning now has a warm spell for the weekend and this slows down any drop:

11th: 20.1 (17.8)
12th: 19.6 (13.6)
13th: 19.2 (14.9)
14th: 18.9 (14.8)
15th: 18.8 (17.1)
16th: 18.9 (19.8)
17th: 18.9 (19.9)
18th: 18.8 (16.1)
19th: 18.4 (11.6)
20th: 18.0 (11.7)
21st:  17.8 (12.3)
22nd: 17.6 (14.7)
23rd: 17.6 (15.8)
24th: 17.6 (17.8)
25th: 17.5 (16.0)
26th: 17.4 (15.8)

So there would be a good chance of the CET record from 2006 being broken if that run came off. However whether we end up with a cool north-westerly or warm south-easterly this coming weekend will be decided by the finest of margins.

[TwisterGirl81]

I'm going to guess the September CET to be 17.1   Whats the highest September CET ever recorded please?

[The PIT]

Sunny Sheffield up to 20.3C +4.3C above average. Rainfall 1.5mm 2.3% of the monthly average.

So the fairly dry spell continuing here and the lower max offset more by the high overnight low.

 

[Don]

10 minutes ago, TwisterGirl81 said:

I'm going to guess the September CET to be 17.1   Whats the highest September CET ever recorded please?

You're too late lol!  Current September CET record is 16.9C back in 2006, but that might be on its last legs!!