GaWx

Also, the UKMET, one of the top tier models, interacts with Humberto and goes well OTS from the SE US per my post above this.

12Z UKMET: At hour 120, 993 mb Humberto, which is within only 500 miles ENE of 1000 mb 94L, causes 94L (which had been moving mainly NNW) to then get sucked toward it as 94L then suddenly turns SSE, then ESE, and then ENE to well OTS (near 27N, 72W)NEW TROPICAL CYCLONE FORECAST TO DEVELOP AFTER 54 HOURSFORECAST POSITION AT T+ 54 : 21.1N 76.5WLEAD CENTRAL MAXIMUM WINDVERIFYING TIME TIME POSITION PRESSURE (MB) SPEED (KNOTS)-------------- ---- -------- ------------- -------------0000UTC 28.09.2025 60 22.2N 76.2W 1006 311200UTC 28.09.2025 72 23.5N 76.9W 1006 320000UTC 29.09.2025 84 24.1N 77.4W 1004 331200UTC 29.09.2025 96 25.9N 78.3W 1004 390000UTC 30.09.2025 108 25.8N 77.8W 1002 381200UTC 30.09.2025 120 26.4N 78.1W 1000 370000UTC 01.10.2025 132 25.4N 77.6W 999 371200UTC 01.10.2025 144 25.0N 76.5W 997 430000UTC 02.10.2025 156 25.4N 74.8W 995 461200UTC 02.10.2025 168 26.9N 72.2W 991 47——————So far at 12Z for major operationals-GFS hits just S of Georgetown, SC, Mon PM (9/29) as a H (with strong support from GEFS, it’s most ominous run by far yet for SE US)-Icon, UKMET, CMC thanks to Fujiwhara go safely OTS from SE US-Euro next-JMA only out to 72 so far (can’t tell yet): edit now out to 192: thanks to Fujiwara, no US landfall as the 2 storms combine

Tropical Weather Outlook NWS National Hurricane Center Miami FL 200 AM EDT Thu Sep 25 2025 Eastern Caribbean Sea (AL94): A tropical wave centered near the Dominican Republic continues to produces widespread disorganized showers and thunderstorms. The wave is expected to move west-northwestward around 10 to 15 mph, spreading heavy rainfall and gusty winds across Puerto Rico and the Dominican Republic through today. The system is then expected to slow down and turn northwestward when it reaches the southwestern Atlantic. A tropical depression is likely to form when the disturbance is in the vicinity of the Bahamas late this week. Interests in Puerto Rico, the Dominican Republic, Haiti, the Turks and Caicos Islands, and the Bahamas should monitor the progress of this system. * Formation chance through 48 hours...medium...50 percent. * Formation chance through 7 days...high...80 percent. Forecaster Bucci

The 0Z EPS is by far the most ominous for the SE US (including some that get into the Gulf) with a whopping ~75% of the members hitting or skimming. Some of these are very weak (not full TCs) while ~1/3 of the hits are strong.

0Z Euro, just like the 0Z CMC, hits Georgetown, SC, on Monday evening (probably because it was further N than Humberto) though it isn’t as strong as the CMC (989 mb per WxBell): So, of major 0Z ops, Euro and CMC hit Georgetown while UKMET, GFS, and Icon stay well offshore.

But the 0Z GFS has 94L no stronger than the high 980s while it has Humberto ~25 mb stronger (~963 mb). Were you aware of that? So, considering that, wouldn’t it make sense for Humberto to dominate?

0Z GEFS: the most threatening run yet to the SE US (even more than 18Z):

1. 0Z CMC Georgetown, SC hit with 975 mb H as not as strong Humberto (983 mb) doesn’t dominate: 2. 0Z GFS is safely OTS with Fujiwara from Humberto.

0Z UKMET: TD forms Mon night NW Bahamas, initially then drifts slowly NW followed by a stall and dissipation as the much stronger Humberto only ~500 miles east takes over: NEW TROPICAL CYCLONE FORECAST TO DEVELOP AFTER 102 HOURS FORECAST POSITION AT T+102 : 25.0N 77.5W LEAD CENTRAL MAXIMUM WIND VERIFYING TIME TIME POSITION PRESSURE (MB) SPEED (KNOTS) -------------- ---- -------- ------------- ------------- 1200UTC 29.09.2025 108 25.9N 78.2W 1008 27 0000UTC 30.09.2025 120 26.1N 78.3W 1007 23 1200UTC 30.09.2025 132 26.1N 78.1W 1007 20 0000UTC 01.10.2025 144 CEASED TRACKING

0Z Icon: Humberto pulls 94L ESE to keep it safely away:

Big news from Australia’s BoM: their model progs have just switched from 3.4 to relative 3.4 (akin to RONI)! Relative Niño indices Traditional Niño index values were used at the Bureau of Meteorology until September 2025. From September 2025, the Bureau uses Relative Niño indices, which measure sea surface temperature anomalies in the tropical Pacific Ocean in the Niño regions, but calculated relative to the global tropical region temperature anomaly. This is to relate the indices more closely to the localised processes associated with ENSO, rather than larger-scale tropical SST features such as global warming. Example: The Relative Niño3.4 index calculation: Relative Niño3.4 = S x [(Niño3.4obs – Niño3.4clim) – (Tropical Meanobs – Tropical Meanclim)] Here’s the latest BoM relative 3.4 model prog for Relative 3.4, which has a low of -0.7C for OND: http://www.bom.gov.au/climate/ocean/outlooks/index.shtml?index=nino34#region=NINO34 @snowman19

Update: -Season’s ACE is now up to 57.2. -Gabrielle has exceeded earlier progs and is now on its own progged to get ACE to ~60. -Humberto has been declared and is progged to add ACE of ~13 through Sept 30th though with lots of uncertainty, including upside to ~17-20. -That would get ACE to ~73-80. -But that’s not necessarily all as models are now significantly more bullish on still another TC by late this week from Invest 94L. A great level of uncertainty rests with 94L at this very early stage. The upside limit on that through Sept 30 is ~~10. -So, current rough projections are significantly higher for ACE as of Sept 30th. In my quoted prog from 3 days ago, I had the upside at 65-70. That upside limit has since risen to ~83-90. That compares to the 1991-2020 average of 94 through Sept. 30. Thus, if this upside range of 83-90 were to verify, Sept 30th ACE could rise all the way to only a little below the active 30 year average! -Oct-Dec 30 year avg is 28. So, if we were to get to 90 as of Sept 30th, getting to an end of season well over 100 would then be favored along with a reasonable upside of ~130-140 vs 1991-2020 avg of 122. That upside potential is extra realistic because of 1. mainly favorable MJO progged for next few weeks 2. weak La Niña on RONI basis is correlated most to above avg ACE late season 3. Euro Weeklies are active @snowman19@PhiEaglesfan712

Tropical Weather Outlook NWS National Hurricane Center Miami FL 800 PM EDT Wed Sep 24 2025 For the North Atlantic...Caribbean Sea and the Gulf of America: Eastern Caribbean Sea (AL94): Showers and thunderstorms have become better organized since yesterday in association with a tropical wave centered near Puerto Rico. This wave is expected to move west-northwestward around 10 to 15 mph, spreading heavy rainfall and gusty winds across Puerto Rico and the Dominican Republic through early tomorrow. The system is then expected to slow down and turn northwestward when it reaches the southwestern Atlantic. A tropical depression is likely to form when the disturbance is in the vicinity of the Bahamas late this week. Interests in Puerto Rico, the Dominican Republic, the Turks and Caicos Islands, and the Bahamas should monitor the progress of this system. * Formation chance through 48 hours...medium...40 percent. * Formation chance through 7 days...high...80 percent. Public Advisories on Humberto are issued under WMO header WTNT33 KNHC and under AWIPS header MIATCPAT3. Forecast/Advisories on Humberto are issued under WMO header WTNT23 KNHC and under AWIPS header MIATCMAT3. Forecaster Blake

I recommend folks who are curious follow the Invest 94L thread. If 94L isn’t pulled toward Humberto (via Fujiwhara), portions of the SE US may be in danger of a hit from 94L per the 12Z EPS, 18Z Icon, and others. In addition, the MJO is forecasted to be in phase 2 9/27-10/3. That has been the single most dangerous phase for the Conus overall since 1975 during Jul-Sept overall.

Example: 18Z Icon: no Fujiwhara and 94L gets stuck under the strengthening US Great Lakes ridge and subsequently turns NW toward C FL: Edit: And the GEFS/EPS are forecasting this to be during the potentially dangerous phase 2.

Followup: Upon closer inspection, 40% (20) of 12Z EPS members affect a portion of the SE with either a TC direct landfall, a skirting of the coast, or a weak remnant. Also, a clear majority of members that weren’t steered by a Fujiwhara from Humberto were in that 40%. So, whether or not Humberto pulls 94L into it might turn out to be the crucial factor for whether or not the SE US is threatened.

The 12Z EPS, like 0Z and 12Z of yesterday, actually has an uncomfortably high # of members (10+/20%+) hitting the SE US 9/28-10/4, which is earlier than the 10/5-7 12Z Euro freakish US hit. One thing that’s a bit concerning is the forecasted MJO phase 2 by both GEFS and EPS for 9/27-10/3. As I posted about last month, phase 2 has had (whether inside or outside the circle) by a wide margin the highest % (after taking into account % of days in each phase) of Conus Jul-Sept MH hits and along with phase 8 the highest % of H hits since 1975. GEFS EPS

12Z UK 94L: TD just NE of C Bahamas moving ESE NEW TROPICAL CYCLONE FORECAST TO DEVELOP AFTER 108 HOURS FORECAST POSITION AT T+108 : 24.5N 77.2W LEAD CENTRAL MAXIMUM WIND VERIFYING TIME TIME POSITION PRESSURE (MB) SPEED (KNOTS) -------------- ---- -------- ------------- ------------- 0000UTC 29.09.2025 108 24.5N 77.2W 1008 28 1200UTC 29.09.2025 120 25.0N 77.0W 1008 27 0000UTC 30.09.2025 132 25.0N 77.1W 1007 27 1200UTC 30.09.2025 144 24.4N 76.6W 1006 24 0000UTC 01.10.2025 156 23.9N 75.0W 1005 25 1200UTC 01.10.2025 168 CEASED TRACKING

12Z UK just W of Bermuda TROPICAL DEPRESSION 93L ANALYSED POSITION : 19.7N 53.9W ATCF IDENTIFIER : AL932025 LEAD CENTRAL MAXIMUM WIND VERIFYING TIME TIME POSITION PRESSURE (MB) SPEED (KNOTS) -------------- ---- -------- ------------- ------------- 1200UTC 24.09.2025 0 19.7N 53.9W 1014 33 0000UTC 25.09.2025 12 20.6N 56.0W 1013 32 1200UTC 25.09.2025 24 21.3N 57.4W 1012 33 0000UTC 26.09.2025 36 21.7N 57.9W 1009 34 1200UTC 26.09.2025 48 21.7N 58.5W 1007 35 0000UTC 27.09.2025 60 22.0N 59.1W 1005 42 1200UTC 27.09.2025 72 22.0N 60.3W 1003 44 0000UTC 28.09.2025 84 22.2N 61.0W 1000 44 1200UTC 28.09.2025 96 22.8N 63.0W 998 47 0000UTC 29.09.2025 108 23.7N 64.5W 994 49 1200UTC 29.09.2025 120 24.5N 66.3W 992 52 0000UTC 30.09.2025 132 25.6N 67.8W 991 56 1200UTC 30.09.2025 144 27.3N 68.4W 991 54 0000UTC 01.10.2025 156 29.1N 67.8W 984 59 1200UTC 01.10.2025 168 31.9N 66.6W 972 61

12Z Euro: After forming in the Bahamas, it recurves away from the SE US and the center just misses Bermuda to the NW as it did for 93L two days earlier in this run. Then it turns back NW before ultimately turning back NE missing the NE US and barely missing Newfoundland.

94L 6Z Euro at 144 had a strengthening 998 TS moving NNW N of the Bahamas threatening the SE US. 6Z Icon at 120 was well E of Euro 6Z GFS had nothing from this, alone, although it appears to combine its vorticity with 93L and develop that well offshore —————- No UK run has had this as a TC AFAIK as of then. But 12Z UK: TD in NW Bahamas that drifts NE NEW TROPICAL CYCLONE FORECAST TO DEVELOP AFTER 138 HOURS FORECAST POSITION AT T+138 : 25.0N 77.1W LEAD CENTRAL MAXIMUM WIND VERIFYING TIME TIME POSITION PRESSURE (MB) SPEED (KNOTS) -------------- ---- -------- ------------- ------------- 1200UTC 29.09.2025 144 25.6N 76.9W 1010 30 0000UTC 30.09.2025 156 26.0N 76.2W 1009 24 1200UTC 30.09.2025 168 26.9N 74.2W 1008 27

0Z Euro has a 1006 TS hit NC 9/29

18Z Euro has a 1001 TS headed NNW in the direction of NC at 30N, 75W at 144

The 12Z slams Bermuda with this on 10/1 as a 954 MH.

The brand new (12Z) Euro has this on 9/29 hit NC as a TD.