GaWx

Indeed! The potential for this to be a huge ACE producer along with providing lots of beautiful satellite pics is way up there. 12Z UKMET stronger than 0Z and is a little N of prior run, but it is ~300-350 miles WNW/W of the Euro/CMC/GFS at 168 (end of run) implying not a guarantee it would miss the CONUS, especially NE, had it gone out further: NEW TROPICAL CYCLONE FORECAST TO DEVELOP AFTER 30 HOURS FORECAST POSITION AT T+ 30 : 13.2N 39.8W LEAD CENTRAL MAXIMUM WIND VERIFYING TIME TIME POSITION PRESSURE (MB) SPEED (KNOTS) -------------- ---- -------- ------------- ------------- 0000UTC 06.09.2023 36 13.8N 41.3W 1010 25 1200UTC 06.09.2023 48 14.4N 44.5W 1007 33 0000UTC 07.09.2023 60 15.7N 46.4W 1007 39 1200UTC 07.09.2023 72 16.9N 49.0W 1005 34 0000UTC 08.09.2023 84 17.8N 51.8W 1005 32 1200UTC 08.09.2023 96 18.9N 55.3W 1005 34 0000UTC 09.09.2023 108 19.9N 58.2W 1005 31 1200UTC 09.09.2023 120 20.2N 60.9W 1004 41 0000UTC 10.09.2023 132 21.1N 63.8W 1000 48 1200UTC 10.09.2023 144 21.7N 65.6W 997 51 0000UTC 11.09.2023 156 22.8N 67.5W 994 61 1200UTC 11.09.2023 168 23.7N 69.1W 993 57

Fortunately for CONUS it appears about to recurve in the run.

12Z Euro is much stronger than the 0Z and is a beast (930s SLP) north of the Caribbean.

I assume you realize that climo heavily favors a miss of the CONUS from a TCG in the E MDR in Sept, especially with it not La Niña. Climo based odds are somewhere around 80% of no CONUS hit, easily the best bet. However, I assume you agree that the problem this far out, especially with no TC center to track yet, is that nobody knows for sure that this won't be one of the 20% that do hit. It isn't as if the chance were something tiny like 5%. Also, if TCG doesn't occur until the W MDR, then that 80% stat becomes irrelevant. Over the next few days we should get a clearer picture. We need to make sure that this won't be a pretty rare long tracking Sep El Niño US hit like Florence of 2018, Ivan of 2004, and Frederic of 1979. Granted, those three were all during a weak El Niño. However, 2023's much stronger El Nino has yet to act much like one. One thing I will say about the GFS is that it may have a left bias these days based on how it did with Ian and Idalia. Any thoughts about this? Edit: 0Z UKMET (goes out 168 hours) is nearly identical to its prior run trackwise though it is weaker. 0Z EPS is pretty similar to its prior couple of runs strongly favoring no NE Caribbean, Bahamas, or CONUS hit.

0Z Euro fits in well with the consensus of the last couple of EPS runs with a recurve near 67W and no land hit though it might have gotten close to Bermuda might had the run continued. It is at a very powerful 941 mb at 240!

So, JJA RONI of 0.57 is a whopping 0.49 cooler than the JJA ONI of 1.06. The 0.49 is possibly the largest amount cooler on record for RONI vs ONI.

Excellent point. Thus, what's usually analyzed regarding whether or not Nino 4 is warmer than the E zones are anomalies rather than absolutes. If we were instead going by absolutes, Nino 4 would just about always be warmer in all months since its base climo is much warmer. In August as you stated, there hasn't been even one El Niño since at least 1951-2 that wasn't warmest in Nino 4. I can find only two El Niños since 1950 for which Nino 4 isn't warmer in all of D, J, and F than all of the other three zones in terms of absolutes: 1982-3 -Jan was warmer in 3.4 than in 4 -Feb was warmer in both 3 and 3.4 than in 4 -DJF was barely warmer in 3.4 than in 4 1997-8 -Feb was warmer in 3 than in 4 ------------------ -So, regarding DJF, I've found no single month warmer in 1+2 than in 4 -Regarding DJF averaged out, I've found none warmer in either 1+2 or 3 vs 4. But 1982-3 was warmer (although only barely) in 3.4 vs 4. -So, anomalies are what are normally compared between regions.

I use the conservative UKMET much more for position than for strength. It was the best by a good margin for Ian and one of the best for Irma and Idalia once within a few days of landfall. For strength, it is the trend rather than the actuals that are usually more informative.

The 12Z JMA, admittedly inferior for the tropics, has an obviously worrisome position at 192 in the Caribbean just S of DR.

When looking at the 12Z EPS 228 vs 0Z EPS 240, the consensus is similarly keeping the risk to the corridor from the NE Caribbean to the Bahamas pretty low (~10% based on ~5 of 51 hitting Bahamas) and to the region well east that includes Bermuda significantly higher. The bulk of the members cross into the box that covers 22-32N, 60-70W. (Bermuda is near 32N, 65W.) Hardly any are (aiming) west of 75W. Verbatim, this run suggests very low risk to the CONUS/Canada, similar to the prior run. There are once again many very powerful hurricanes on this run.

UKMET 0Z 168: 0000UTC 10.09.2023 168 19.5N 62.1W 1005 32 UKMET 12Z 156: 0000UTC 10.09.2023 156 20.6N 64.0W 1002 49 So, 12Z UK at 156 is a bit WNW of 0Z at 168 and stronger. Here's the complete 12Z UK run: NEW TROPICAL CYCLONE FORECAST TO DEVELOP AFTER 72 HOURS FORECAST POSITION AT T+ 72 : 14.3N 44.1W LEAD CENTRAL MAXIMUM WIND VERIFYING TIME TIME POSITION PRESSURE (MB) SPEED (KNOTS) -------------- ---- -------- ------------- ------------- 1200UTC 06.09.2023 72 14.3N 44.1W 1009 27 0000UTC 07.09.2023 84 14.7N 46.4W 1008 36 1200UTC 07.09.2023 96 15.7N 48.7W 1007 34 0000UTC 08.09.2023 108 16.4N 51.6W 1006 30 1200UTC 08.09.2023 120 17.2N 54.8W 1005 36 0000UTC 09.09.2023 132 18.1N 58.1W 1004 36 1200UTC 09.09.2023 144 19.3N 61.4W 1003 44 0000UTC 10.09.2023 156 20.6N 64.0W 1002 49 1200UTC 10.09.2023 168 21.5N 67.3W 1000 54 Looking at H5, there is a pretty strong persistent E coast trough and stationary TX strong (594 dm) ridge. The trough is stronger than it is on the other models. If that were to verify, that would imo likely recurve it away from the SE US like the model consensus is still suggesting. However, from NC Outer Banks north wouldn't be as clearcut. Again, this is strictly per the 12Z UKMET, not a forecast. H5: scroll down https://weather.us/model-charts/gbr/2023090312/north-america/geopotential-height-500hpa/20230910-1200z.html

Well, actually, the Nino 3 anomaly was slightly warmer than 3.4 in December. So, I guess it can be considered east-based to start. But Nino 3.4 was barely warmer in Jan and significantly warmer in Feb leading to a higher DJF in 3.4. I thought you were calling 1972-3 east-based, overall. If not, I misunderstood you. Nino 1+2 averaged cooler than both, especially in Jan and Feb.

1. Why are you calling 1972-3 east-based? I see per ERSST that DJF anomalies averaged higher in 3.4 than in any other region. They're slightly higher than Nino 3 and significantly higher than 1+2. Nino 4 anomalies are much lower than the other three regions. So, it certainly isn't west-based. But with 3.4 having the highest, wouldn't this be considered central rather than east based? The most central region has the highest anomalies. 2. I assume you agree that east-based doesn't always mean mild E US. 1976-7 had the highest anomalies of the four regions in Nino 3 and that was a frigid winter. I do realize it being weak helped its chances.

After two runs without TCG being noted on the UKMET, the new run (0Z) has TCG. So, together with a much stronger CMC vs 12Z, there is some reversal of recent runs' weakening trends despite the 0Z GFS being similar to its recent weaker runs. 0Z UKMET: moving WNW at 15 just N of Leewards at 168: NEW TROPICAL CYCLONE FORECAST TO DEVELOP AFTER 84 HOURS FORECAST POSITION AT T+ 84 : 14.8N 44.0W LEAD CENTRAL MAXIMUM WIND VERIFYING TIME TIME POSITION PRESSURE (MB) SPEED (KNOTS) -------------- ---- -------- ------------- ------------- 1200UTC 06.09.2023 84 14.8N 44.0W 1010 24 0000UTC 07.09.2023 96 15.7N 45.9W 1009 27 1200UTC 07.09.2023 108 16.4N 47.8W 1008 29 0000UTC 08.09.2023 120 17.2N 50.6W 1008 26 1200UTC 08.09.2023 132 17.8N 53.7W 1008 29 0000UTC 09.09.2023 144 18.3N 56.3W 1007 27 1200UTC 09.09.2023 156 18.6N 59.6W 1007 31 0000UTC 10.09.2023 168 19.5N 62.1W 1005 32

The 12Z EPS at 228 is similar to the 0Z EPS at 240 with <20% of members threatening the NE Caribbean, Bahamas, or CONUS. Of those that do, two appear to be cat 4-5 with a 923 and a 933 as of 240 both moving WNW near/toward the Bahamas. Bermuda is still threatened by a good # and there are once again many Hs.

Down to 994 at 192.

Yep although it still is the strongest of the 12Z runs at 144. Also, the 0Z Euro had similar weakening 132-156 followed by restrengthening. I'll be looking to see if the 12Z is similar.

12Z Euro is strongest of the 12Z models as of 120 and pretty close to earlier runs.

The 12Z model consensus is weaker/delayed on TCG. Not only does the GFS have very little early in the run (GFS TCG is delayed til the Caribbean), the CMC is similar. Plus the last few ICONs have been weaker than recent days. Also, the last two UK (goes out 168) have no TC after many in a row with it. Trend? Mean further west if there is ever TCG?

NDJ

The CFS ONI peak has come back way down from +2.15 just a few weeks ago to ~+1.80-1.85.

For this same AEW, I count 27 12Z EPS members (53%) with a H. That is more than the 0Z and is as high as any EPS I can recall for any as yet to develop system in the MDR this season to date. So, at a minimum, this looks likely to be a big ACE producer giving us pretty satellite pics. Edited

From the 12Z UKMET hour 168: Surface showing TC 300 miles E of Leewards (moving WNW at 15): scroll down https://weather.us/model-charts/gbr/2023090112/americas/sea-level-pressure/20230908-1200z.html -------------------------- H5: In addition to being a threat to the NE Caribbean, the 12Z UKMET doesn't yet look like anything close to a guarantee to not hit the CONUS although the best bet this far out is a miss based on 75%+ of E MDR systems doing just that: scroll down https://weather.us/model-charts/gbr/2023090112/americas/geopotential-height-500hpa/20230908-1200z.html

It won't be +1.2. It will be either +1.0 or +1.1. August OISST is ~+1.3, which translates to ERSST likely being slightly cooler than that (~+1.25?). June was 0.84 and July was +1.00. So, if Aug ERSST turns out to be +1.25, that would mean JJA average of +1.03, which would round down to +1.0 for the table. But if Aug ERSST were to come in at +1.31+, that would give a JJA of +1.05+, which would be reported as +1.1 in the table. So, that's why I say +1.0 or +1.1. To get a +1.2, you'd need a +1.6 for Aug, which isn't happening.

-Usually the best bet for an E MDR system since 75%+ don't hit the US although nowhere near a safe bet at least yet imo -12Z UKMET: still has TCG but unlike the prior run having TCG on Sunday, this waits til Wednesday (9/6). With the delay, it is notably weaker but is still in a potentially dangerous position at 168 (9/8) 300 miles E of the Leewards moving WNW at 15 mph: NEW TROPICAL CYCLONE FORECAST TO DEVELOP AFTER 120 HOURS FORECAST POSITION AT T+120 : 14.2N 44.1W LEAD CENTRAL MAXIMUM WIND VERIFYING TIME TIME POSITION PRESSURE (MB) SPEED (KNOTS) -------------- ---- -------- ------------- ------------- 1200UTC 06.09.2023 120 14.2N 44.1W 1010 27 0000UTC 07.09.2023 132 14.1N 46.7W 1009 29 1200UTC 07.09.2023 144 14.9N 49.0W 1007 37 0000UTC 08.09.2023 156 15.4N 51.8W 1007 31 1200UTC 08.09.2023 168 16.1N 54.9W 1007 34