GaWx

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

The 12Z Euro is another that still has nothing of significance, far different from the GFS/CMC/Euro-AI. The 12Z GEFS favors FL including panhandle whereas the GEPS is about 50% FL Big Bend south and 50% E LA to AL. For those not familiar: Operationals are of limited use this far out because they’re like throwing darts to a pretty far away dartboard. The ensemble members are also darts to a far away dartboard but there are a bunch of darts at once to better give us tendencies/trends.

Indeed, I agree that CC/AGW is real and significant. My point to TT was that the UHI portion for large cities like Phoenix and LV shouldn’t be dismissed as insignificant. He said, “I’ve never bought it that the urban he Island is a big enough factor in this thing”. That’s what I was responding to. Perhaps I misinterpreted him. Maybe he just meant that UHI isn’t the dominant metric, which I’d lean toward though I could see it approach 50% in some of the faster growing large metros like LV.

Yeah, I realize that we’ve all been looking at Atlantic ACE only and I still feel like you that there’s a notable negative correlation of that and SSN. This graph is based on worldwide MH count, obviously not at all the same as ATL ACE. If I get the time, I may due to curiosity look at just Atlantic MH to see if there appears to be a decent inverse correlation to SSN. One would think so but you never know. Regardless, the worldwide MH count apparently not negatively correlating to SSN admittedly makes me wonder why. Could there be something about the Atlantic that makes it more conducive to negatively correlating to SSN than other basins? If so, I wonder what that could be. Interesting to think about!

Below is a repost of that Ryan Maue graph posted earlier today. Note that the global MH freq is the sum of the prior 3 years as opposed to the 3 years centered on that date. If this had instead been the latter, it would have suggested a notable inverse relationship of global MH frequency and SSN. But it isn’t. Calculations 1/86: MH 3 yr sum peak 71/SSN prior 3 yr avg 57 1/89: MH 3 yr sum dip 56/SSN prior 3 yr avg 64 9/94: MH 3 yr sum peak 92/SSN prior 3 yr avg 100 7/01: MH 3 yr sum dip 62/SSN prior 3 yr avg 148 3/07: MH 3 yr sum peak 87/SSN prior 3 yr avg 41 10/13: MH 3 yr sum dip 55/SSN prior 3 yr avg 81 9/16: MH 3 yr sum peak 94/SSN prior 3 yr avg 82 3/23: MH 3 yr sum dip 53/SSN prior 3 yr avg 51 Analysis -Highest MH 3 yr sum peaks (94, 92) when prior 3 yr SSN avg not low (82, 100) -Lowest MH 3 yr sum dips (53, 55) when prior 3 yr SSN avg not high (51, 81) -So, two highest MH 3 yr sum peaks (avg 93) had avg prior 3 yr SSN avg up at 91 while two lowest MH 3 yr dips (avg 54) had avg prior 3 yr SSN down at 66. Conclusion I can’t conclude that there’s even a very limited negative correlation of SSN and worldwide MH based on this data. The graph is deceiving (not necessarily intentional). Had this same graph been measuring 3 yr MH sums centered on each date instead of the 3 yrs prior, I would have concluded a decent negative correlation of MH count and SSN just from looking at this with no calculations needed. But it’s not. Those MH peaks/dips that you see are the sums of the 3 years prior. So, you can’t just look at those MH peaks/dips (blue) and go directly down to the SSN (red). You instead have to look at the avg of the reds for the 3 yrs prior to each MH peak/dip. Monthly SSN: https://www.sidc.be/SILSO/DATA/SN_m_tot_V2.0.txt

For the 8th run in a row the CMC has a TC form in the W Caribbean 9/21-2 and move N toward the U.S. The 0Z GFS also has a similar storm that comes in a little later. Before that interestingly enough, it does something similar to the 12Z Euro forming a weak LLC SE of NYC at least partially from the remnants of PTC-8. It similarly moves S and gets down to 1001 mb. But instead of turning W to NC, it then turns SW and goes over C FL while opening up.

The CRW Nino 3.4 updated for the first time in two months! It has usually been either very close to or slightly warmer than OISST. But currently it is slightly cooler at -0.38: OISST has resumed cooling (now at -0.28):

The Euro Weeklies, which have been quite impressive both with the very active early season as well as the relatively quiet peak season, are like they have for many days still calling for weekly ACE rising to near normal late Sep and to well above normal in the first 2 weeks of Oct, like it or not.

The Phoenix area has grown nearly tenfold since 1960 and is now at 4.8 million. It has doubled in size just in the last 30 years. Minimizing the importance of UHI as a significant factor seems presumptuous to me. I’m not saying I think it is larger than CC (I fully believe in AGW), but rather I’m saying I think it is far from trivial and that it wouldn’t surprise me if it something like 30-40%: https://www.macrotrends.net/global-metrics/cities/23099/phoenix/population

The late portion of the 12Z Euro with its TC heading W toward NC is more of a fwiw/mainly for entertainment run than the late portion of the 12Z CMC imo because unlike the CMC this Euro is very different from prior Euros. Interestingly, this isn’t at all from a tropical origin and is instead related to a combo of PTC-8’s vorticity going NE and the vorticity associated with that 32N, 70W circulation that I mentioned earlier going N. They combine and get stuck near NYC under a new Rex block. Then a new surface low forms Wed night (only 60 hours from now), moves S, and then turns W late. I want to first see if there will even be a surface low that forms SE of NYC wed night. Also, I’m going to keep watching that circulation near 32N, 70W as it heads N.

FEMA/NFIP flood insurance covers flooding from heavy rain from whatever the source. But homeowner’s normally doesn’t pay for flooding from rainfall. It pays to have FEMA/NFIP. It isn’t even expensive outside of high risk flood zones. https://flood.nc.gov/ncflood/insuranceagent.html#:~:text=Is flood insurance available everywhere,NC communities are participating communities.

This was even worse than Florence in some areas due to it falling within a much shorter period of time. This shows you don’t need a TS or STS to have near biblical effects.