GaWx

12Z Euro: W Gulf at 240

Nothing is black and white. I’m just saying it may be one factor contributing to the tropics waking up.

The SSN mean for Sept to date has been much lower than the 215 of Aug. That is especially the case the last 10 days, which have averaged only ~128. There’s no way to know but perhaps this is one of the reasons the tropical Atlantic is waking up and likely soon headed toward normal to above average activity. Perhaps Atlantic tropical instability is increasing and, if so, the solar downturn may be contributing to that: 2024 09 01 2024.668 182 14.5 27 35 2024 09 02 2024.671 195 20.7 26 33 2024 09 03 2024.673 180 21.2 20 23 2024 09 04 2024.676 174 26.1 21 26 2024 09 05 2024.679 181 13.1 15 20 2024 09 06 2024.682 189 13.3 19 24 2024 09 07 2024.684 168 17.8 24 29 2024 09 08 2024.687 171 18.7 20 26 2024 09 09 2024.690 156 19.1 23 26 2024 09 10 2024.693 149 12.8 24 30 2024 09 11 2024.695 153 15.4 29 34 2024 09 12 2024.698 144 11.6 24 28 2024 09 13 2024.701 118 13.1 26 31 2024 09 14 2024.704 117 10.6 24 31 2024 09 15 2024.706 100 14.1 22 27 2024 09 16 2024.709 142 16.2 22 27 2024 09 17 2024.712 141 13.4 28 36 2024 09 18 2024.714 109 9.9 24 28 2024 09 19 2024.717 109 11.1 25 31

The SSN mean for Sept to date has been much lower than the 215 of Aug. That is especially the case the last 10 days, which have averaged only ~128. There’s no way to know but perhaps this is one of the reasons the tropical Atlantic is waking up and likely soon headed toward normal to above average activity. Perhaps Atlantic tropical instability is increasing and, if so, the solar downturn may be contributing to that: 2024 09 01 2024.668 182 14.5 27 35 2024 09 02 2024.671 195 20.7 26 33 2024 09 03 2024.673 180 21.2 20 23 2024 09 04 2024.676 174 26.1 21 26 2024 09 05 2024.679 181 13.1 15 20 2024 09 06 2024.682 189 13.3 19 24 2024 09 07 2024.684 168 17.8 24 29 2024 09 08 2024.687 171 18.7 20 26 2024 09 09 2024.690 156 19.1 23 26 2024 09 10 2024.693 149 12.8 24 30 2024 09 11 2024.695 153 15.4 29 34 2024 09 12 2024.698 144 11.6 24 28 2024 09 13 2024.701 118 13.1 26 31 2024 09 14 2024.704 117 10.6 24 31 2024 09 15 2024.706 100 14.1 22 27 2024 09 16 2024.709 142 16.2 22 27 2024 09 17 2024.712 141 13.4 28 36 2024 09 18 2024.714 109 9.9 24 28 2024 09 19 2024.717 109 11.1 25 31

It is back on the UKMET (12Z) with it becoming a TC at 168 (12Z on 9/26) in NW Caribbean 150 miles SW of W tip of Cuba: NEW TROPICAL CYCLONE FORECAST TO DEVELOP AFTER 168 HOURS FORECAST POSITION AT T+168 : 20.1N 86.0W LEAD CENTRAL MAXIMUM WIND VERIFYING TIME TIME POSITION PRESSURE (MB) SPEED (KNOTS) -------------- ---- -------- ------------- ------------- 1200UTC 26.09.2024 168 20.1N 86.0W 1004 27

Looks like Euro will likely be W again with whatever forms on the run per early maps.

0Z GEFS says that the 0Z GFS is a major W outlier as just about all members recurve in the E Gulf. This is about the most threatening GEFS to W FL from Big Bend S of any run yet. 0Z UKMET has no TC through 168.

I storms have been extra damaging and/or deadly on the CONUS since Irene of 1999 and Isabel of 2003. Afterward, there was Ivan of 2004, Ike of 2008, Irene of 2011, Isaac of 2012, Irma of 2017, Isaias of 2020, Ida of 2021, Ian of 2022, and Idalia of 2023. Very damaging or deadly H storms for CONUS: Hazel of 1954, Hilda of 1964, Hugo of 1989, and Harvey of 2017. I storms overall have been the worst by a good margin of any letter for the CONUS the last 25 years.

Look out below! OISST just plunged 0.2 in 24 hours (because it’s playing catch-up) to -0.56 (weak La Niña territory) CRW: -0.55 CDAS: -1.00

12Z Euro: far NE TX 9/28 998 mb 12Z JMA: middle of Gulf 9/26 moving N 1004 mb 12Z Euro ens: quite active with main US threat E LA to Tampa

Other 12Z: -GFS 988 into FL Big Bend early 9/27 and then ENE to N of Daytona -CMC 974 Pensacola late afternoon 9/26

The NHC lemon has just come into the 12Z UKMET’s 168 hour range and it has TCG at 162 in NW Caribbean 200 miles SSW of W top of Cuba moving NNE toward W Cuba on 9/25: NEW TROPICAL CYCLONE FORECAST TO DEVELOP AFTER 162 HOURS FORECAST POSITION AT T+162 : 18.9N 86.2W LEAD CENTRAL MAXIMUM WIND VERIFYING TIME TIME POSITION PRESSURE (MB) SPEED (KNOTS) -------------- ---- -------- ------------- ------------- 1200UTC 25.09.2024 168 19.4N 86.0W 1004 27

Further to what bluewave said the exact opposite, a mean Aleutian low/trough, is best for cold anomalies in the MidAtlantic states and especially the SE US as it is part of a +PNA and usually results in an E US trough and no SE ridge in winter. Now further N into New England and further NW/W into the E Midwest, it isn’t as clearcut as +PNA isn’t as correlated to cold or perhaps none at all if far enough N or NW/W. An Aleutian low is most common in El Niño and Aleutian high is most common in La Niña. That’s why I don’t care for La Niña down here as this often means strong SE ridge. Remember all of those models showing a beautiful Aleutian low at H5 for last winter that I as well as many others were salivating over constantly? It ended up not verifying, which isn’t surprising because seasonal models aren’t at all reliable. That’s why I caution others to not assume the H5 maps for this winter on models like the CFS and Cansips will verify well. My advice as always is to take long range model output, including at 500 mb (H5), with a gigantic grain of salt.

What do you know about the cause of that insanely warm N Pacific area? It wouldn’t surprise me if some anomalies in that +5+ area are +8+! I’ve been reading about underwater seismic activity possibly being a cause. What do you know about that?

Now a lemon: An area of low pressure could form this weekend over the western Caribbean Sea. Thereafter, some slow development of this system is possible through early next week while the system moves slowly to the north or northwest over the northwestern Caribbean Sea.* Formation chance through 48 hours...low...near 0 percent. * Formation chance through 7 days...low...20 percent.

For the first time in a very long time, 3.4 per OISST, CRW, CDAS; OHC, and TAO buoys are all at their coolest of the year to date.

But over a day earlier than prior GFS runs

Chuck, I did a quick and dirty check of 1950-1979 for Oct NAO >+0.5. I did see a large portion of those become -NAO JFM. But here’s my concern about this: - Oct NAO >+0.5 much more common 1950-79 (15 of 30 or 50%) vs 1980-2023 (only 5 of 44 or a mere 11%) - JFM NAO <-0.25 much more common 1951-1979 (17 of 29 or 59%) vs 1980-2024 (only 6 of 45 or 13%) So, of course there is a significantly higher % of +NAO Octs that switch sign for JFM in 1951-79 (a whopping 10 of 15 or 67%) vs in 1980-2024 (only 1 of 5 or 20%). They’re like two different eras to me and thus I like to stick to the current +NAO winter era of last 45 years.

Thanks. I like to just look at 1979-80+ because we’re in a winter +NAO era that started them. I’m still trying to figure out why. I prefer to look at DJF since it’s net winter but I’ll look at JFM since 1979-80. Changes in NAO status when changing to JFM: Additions: 1980, 2013 Deletions: 2011, 2021 Additions: -1980: prior Oct had -0.3 -2013: prior Oct had -2.1 Deletions: -2011: prior Oct had -0.9 -2021: prior Oct had -0.7 ————————— So, net change for last 45 years was essentially a wash JFM vs DJF So, still 1/4 (or 1/3 if keeping neutrals)

I respect Chuck’s extensive leading indicator knowledge. However, he had to have figured this differently from me. My analysis of the last 45 years shows only 25-33% (depending on whether or not one throws out the two neutral Octs) changed sign: 1984: -0.1 neutral (but didn’t change sign if it’s counted) 1986: +1.6 changed sign 1995: +0.2 neutral (did change sign if it’s counted) 2009: -1.0 didn’t change sign 2010: -0.9 didn’t change sign 2020: -0.7 didn’t change sign - So, ignoring the two neutrals, only 1 of 4 (1986) changed sign - If not ignoring two neutrals, still only 2 of 6 changed sign.

But what do you think about the data I just showed, which is for the 6 -NAO winters of the last 45 years? It shows no correlation to a +NAO in Oct.

Taking this further, it has +NAO in Nov-Jan and a -NAO in Feb/Mar. I’m not familiar with Chuck’s work. But I did my own check: there have been 6 -NAOs since 1979-80. Here were the preceding Oct NAOs: 1984: -0.1 1986: +1.6 1995: +0.2 2009: -1.0 2010: -0.9 2020: -0.7 Average Oct NAO: -0.15/neutral with 3 -NAO and 1 +NAO This tells me there’s no correlation of Oct +NAO and winter -NAO based on the last 45 years.

But don’t forget that the mean H5 shown on this and other long range models could easily be wrong. Last winter is just one example. If H5 had even been close, last winter would have been much better. They’ve overall averaged too cold in recent years in the E US.

The 12Z EPS has fwiw a whopping 20% (10) of its 50 members with a H landfalling in the FL Big Bend to Panhandle region. Plus there are a couple of TS hits there, too. That’s a strong signal for so far out. Expect it to change from run to run.

Keep in mind that this table has worldwide MHs rather than just Atlantic MHs. Thus El Niño years’ MHs have actually averaged higher than non-Nino MH due I assume mainly to the Pacific more than making up for the slowing in the Atlantic. For the period 1980-2023, worldwide MHs averaged 24. But that increased to 26 for just El Niño seasons. There have been 7 of these years with 30+ worldwide. Of those 7, 5 were Nino years with the super Nino of 2015 the highest at 39. The other 2 were neutral. So, no Niña years. https://tropical.atmos.colostate.edu/Realtime/index.php?arch&loc=global