GaWx

Fwiw and for the record the 6Z Euro AIFS is the 13th run in a row (back to the 6Z 8/19 run) with a TCG in the vicinity of the Leeward Islands ~Sept 2nd.

Good question. My understanding is (or at least the way I use it) that the required +/- 0.5C for 5 consecutive trimonthly periods is just for whether or not an event is Nino, neutral, or Nina based on ONI. However, because RONI is a pretty new concept and has yet to be used for official classifications, it’s going to be hard (if not impossible) to find anything about requiring 5 consecutive RONI for classifying. But I think it makes perfect sense to use RONI that way. I don’t see why not.

Very well thought out! Thanks for posting this. With my being in a vulnerable location, I hope you’re wrong with the very active peak or if not that people aren’t too badly impacted during the peak. I’d love for the peak to be like 2010. This is a minor point but I do want to point out that 2024 is 3rd highest of satellite era with 1980 also being higher as of today. The graph you show goes back only to 1991. That’s why it shows 2024 as 2nd highest. But since you mentioned 2nd highest of satellite era, I thought I should mention this.

- I believe that Oct is the most dangerous month for a direct landfall on the Gulf coast of FL. - Up here in E GA, Matthew in Oct of 2016 was easily the worst since at least David (1979). - Hazel in Oct of 1954 was one of worst ever in NC/SC and then was a monster well inland in much of E US - Oct of 1898 was another really bad H (in GA and far N FL)

Strong thunderstorms have popped along the seabreeze front and are now over downtown as well as N into lower SC. I’ve heard a good bit of thunder but am not getting any rain at least as of yet. Edit 9:14 PM: The heavy rain has slowly slipped S and now it is falling here. I ended up with ~1”. I actually got a little bit of new flooding into my garage but I took care of that. I’ve been waiting for them to get out here to replace the garage door’s bottom seal. They’ve had a lot of calls due to Debby backing them up.

Euro weeklies mean ACE forecast update vs norm last 7 days (newest far right, which is 0Z of Tue): 8/26-9/1: 50%/60%/50%/50%/50%/30%/20%; Norm 14 9/2-8: 110%/110%/120%/100%/110%/70%/70%; norm 15 9/9-15: 90%/80%/90%/80%/100%/80%/90%; norm 16 9/16-22: 90%; norm 13 So, in today’s Euro Weeklies update regarding the 3 weeks I’ve been following, yesterday’s progged sharp mean ACE drop from 40 to 28 was maintained today. Also, todays added a new week (9/16-22) with a mean of 12 ACE. Thus, today’s Euro Weeklies mean ACE prediction for the 4 week period 8/26-9/22 is 40. This 40 compares to the 1991-2020 avg of 58. So, mean ACE prediction is significantly below the 1991-2020 avg mainly due to weeks 1-2 fwiw. Thoughts? https://charts.ecmwf.int/products/mofc_multi_tcyc_family_frequency/overview/base_time?base_time=202408200000&parameter=Accumulated cyclone energy&valid_time=202409020000

CSU outlook for next 2 weeks (8/20-9/2): most likely near normal with activity more concentrated in 2nd week as one would expect based on models; no surprises in this. They did well with their prior 2 week fcast, which verified mainly due to Ernesto with its favoring of above avg activity: https://tropical.colostate.edu/Forecast/2024-0820.pdf

12Z GEFS: another GEFS that looks rather active for first few days of Sept.

Well, Tahiti had 1019.15 yesterday, the highest daily SLP there since Sep of 2010 and only the 14th day of 1019+ since 1991. There look to be 3 more chances for a 1019+ through Aug 22. Then it will drop, but there are hints of another strong high passing to the S of Tahiti early next week that could easily raise them back above 1018 for a couple of days. These high Tahiti SLPs favor further development of La Niña.

It just missed being a MH during the window ending 9/1 by one day.

Probably not worth that much but fwiw the last 4 Euro-AIFS suggest the area around Puerto Rico may have to watch for a nearby TC ~Sep 3. Again, fwiw. Will be interesting to see what todays Euro weeklies show after yesterday’s sudden pretty sharp downturn (ACE fell to 28 from 40, which is about where it had been for 7 days) for 3 weeks ending mid Sep. So, it still had some activity but was BN. Was that just a blip? The 6Z GEFS is pretty active with many members having a TC in the W basin late.

Ernesto’s total ACE will end up ~15 or just under, which is near the 1991-2020 avg for a hurricane.

I’ve found that most, if not all, of the significant cooling from strong and/or large TCs tends to reverse within a few weeks during early to mid season.

I had just a shortlived shower ~4PM. Nothing measurable.

If the GFS/Euro end up verifying well, there could be as many as 4 straight Tahiti SLPs of 1019+ during Aug 19-22. I’d be very surprised if there isn’t at least one. Keep in mind that higher Tahiti pressure is favored during developing La Niña. There hasn’t been even a single day of 1019+ since 2010! Tahiti SLP 1019+ since 1991: 1019.55: 1994 (Aug) 1019.1, 1019.44: 1996 (June) 1019.3: 1998 (Aug) 1019.28: 1999 (Aug) 1019.24: 2010 (July) 1019.44, 1019.61, 1019.78, 1019.59, 1019.14: 2010 (Sep) 1019.05: 2010 (Sep) -So, there have been only 13 days of Tahiti SLP of 1019+ over the last 33 years with the record high being 1019.78 (Sep of 2010). - This shows there’s been only one time when there were more than two days in a row of that (Sep of 2010). That was during the longest streak on record, 5 days. - This shows that all were during June-Sep with a mean date of Aug. That makes sense because that’s during their winter, when sfc cold high pressures are at their highest SLP of the year. - There is a decent correlation between high Tahiti SLP periods and an active Atlantic tropics mainly 1-3 weeks afterward. That jibes well with the idea of an active Atlantic sometime between very late this month and mid Sep.

If the GFS/Euro end up verifying well, there could be as many as 4 straight Tahiti SLPs of 1019+ during Aug 19-22. I’d be very surprised if there isn’t at least one. Keep in mind that higher Tahiti pressure is favored during developing La Niña. There hasn’t been even a single day of 1019+ since 2010! Tahiti SLP 1019+ since 1991: 1019.55: 1994 (Aug) 1019.1, 1019.44: 1996 (June) 1019.3: 1998 (Aug) 1019.28: 1999 (Aug) 1019.24: 2010 (July) 1019.44, 1019.61, 1019.78, 1019.59, 1019.14: 2010 (Sep) 1019.05: 2010 (Sep) -So, there have been only 13 days of Tahiti SLP of 1019+ over the last 33 years with the record high being 1019.78 (Sep of 2010). - This shows there’s been only one time when there were more than two days in a row of that (Sep of 2010). That was during the longest streak on record, 5 days. - This shows that all were during June-Sep with a mean date of Aug. That makes sense because that’s during their winter, when sfc cold high pressures are at their highest SLP of the year. - There is a decent correlation between high Tahiti SLP periods and an active Atlantic tropics mainly 1-3 weeks afterward. That jibes well with the idea of an active Atlantic sometime between very late this month and mid Sep.

Actually through 2022 BoM interestingly had no discernible bias (some years too warm while others too cold…was a mix that washed out). Then 2023 itself was way too warm as it called for ONI maxes in the high +2s several times vs the actual of ~+2.0 ONI (RONI only ~+1.5). So, I don’t know that I can consider BoM warm biased based on just one year. This is unlike the consistent warm bias of the Euro, especially for non-El Nino years. We’ll have to see how the next few years go for BoM. With this new run down to -0.73 for SON, any warm bias it was showing for 2024 may have finally been corrected. I continue to favor the UKMET somewhat after last year’s stellar performance/steadiness and this year’s steadiness. August UKMET run dipped to -0.94 in NDJ. That may turn out slightly too low. Right now I’m guessing ~-0.75/~-1.25 low for ONI/RONI, in partial deference to the JMA’s rise to -0.56 for its ONI low on its Aug run.

Keep in mind that BoM (AUS-Access) incorporated in this was the prior run, which dipped down only to -0.23 for SON. But as I posted about early this morning, it plunged to ~-0.8 in the brand new run in both Oct and Nov, producing SON way down at -0.73.

While Ernesto is still out there and is near or at its strongest yet continuing to add more ACE (it’s nearing 54 already), ensembles (Euro/GFS) are hinting at a TC in the W basin during the 9-15 day period. It appears to me that AEW(s) coming off Africa ~Aug 24-7 may be the main instigator. I’ve been especially following something coming off ~Aug 24-5, which the last three 12 hourly ICON runs have a surface low from. Also, the Euro Weeklies have been suggesting an increase in activity in early Sep continuing into mid Sept: Euro weeklies ACE forecast vs norm last 7 days (newest far right, which is 0Z of Sunday): 8/26-9/1: 60%/60%/50%/60%/50%/50%/50%; Norm 14 9/2-8: 110%/110%/110%/110%/120%/100%/110%; norm 15 9/9-15: NA/120%/90%/80%/90%/80%/100%; norm 16 So, the weeklies have been pretty consistently calling for ~7 for 8/26-9/1, 17 for 9/2-8, and 16 for 9/9-15. That would get ACE to ~96 after Ernesto finishes at ~56 vs the 1991-2020 avg for 9/15 of 70. That’s if these numbers aren’t underdone. I think they’re more likely underdone than overdone assuming there actually are TCs during this period due to a low ACE bias. In summary, the signal for the last 7 days of Euro weekly runs is for a sharp ramp up to increased activity in early to mid Sep after a somewhat quiet week or so right after Ernesto loses its tropical classification. So, I anticipate only a short quiet period. Then I could easily see something like 3 more TCs late Aug through 9/15, starting as early as with the AEW leaving Africa 8/24-5, with 2-3 of these Hs. That would bring the season to 5-6H by 9/15, well on the way to ~10H for the season. If there are 3H by 9/15, ACE could easily then be ~115 vs a 70 normal, well on the way to a hyper season.

Here's something different and unexpected: the brand new BoM is much colder than the prior run! New run dips to -0.8 in Oct and Nov: Compare that to the run from 2 weeks earlier, that dipped only to -0.3 in Oct!

Line of strong thunderstorms is just crossing through. I ended up with ~0.85”.

I hope you’re right! Although the early season has been active in terms of ACE and hurricanes, I’m not emphasizing that because I’m happy about it. I’m emphasizing it because I like to talk about what has actually happened in comparison to history and don’t like to see misinformation. I love doing statistical based analyses. Nothing would make me happier than to see no more US H landfalls this season. I’d love to see huge busts to the downside vs JB, CSU, etc. I believe that many # of NS forecasts are likely going to bust too high for obvious reasons. Just because I post a lot about hurricanes doesn’t at all mean I’m rooting for these monsters. I post a lot about all kinds of wx (forecasting or obs) whether I want it or not and not just for my location. I had more than enough of a headache from Debby just from a partially flooded garage. I still feel pretty good about my 21/10/5 forecast I made for our contest.

We’ll see what happens down the road. But in the meantime, 2024’s ACE of 51 as of Aug 17th is >triple the normal ACE for the active era for that date of 16 and is 3rd highest since 1951 behind only 2005 and 1980! Aug 17th ACE of 16 averages only 13% of total season mean ACE of 122 for 1991-2020. So, 2024 is well on its way to a potential 200ish hyperactive season. It may not make it and it looks to be quiet for at least a week once Ernesto goes extratropical but it sure has a good head start toward it. Quiet periods even near peak aren’t uncommon in active seasons. https://cyclonicwx.com/climatology/

At Atlanta, 2008-9 had no measurable snow til the heavy wet snow of March 1st that measured 4.2”. This put ATL at 200% of normal and was the heaviest snowstorm since the aforementioned Jan of 2002 4.4” snow. (Temperatures for that winter averaged near normal.) They had only 0.1” in 22-23 with a much warmer winter than 2008-9. ATL has had only 0.6” of snow since Jan of 2018!

The ensembles have been having an intermittent modest signal for possible development in the MDR a few days after a wave comes off Africa ~8/24. So, once Ernesto loses TC status (maybe tomorrow), there will likely be about a week before the next possible TCG. The interim will be a good time to rest up for the potential onslaught coming as most days this month have had a TC bringing ACE all the way up to 51 vs normal of 16, less than 1/3 of that! This is the third highest ACE for the season to date since 1951! There will also be potential for mainly Gulf homegrown late month per JB due to a ridge over troubled waters setup.