GaWx

99L is now a cherry: 1. Eastern Subtropical Atlantic (AL99): Showers and thunderstorms have changed little in organization since this morning in association with an area of low pressure located several hundred miles southwest of the Azores. However, just a small increase in organization is likely to result in the formation of a tropical depression as soon as later today. The system is expected to move slowly over the next couple of days remaining southwest of the Azores, followed by a turn to the southwest by early next week, when environmental conditions are forecast to become less favorable for additional development. * Formation chance through 48 hours...high...70 percent. * Formation chance through 7 days...high...70 percent.

Is 99L going to be the first TC formation of the month? Edouard became a TC in August. When was the last Sept that didn’t have a TC formation by now? 2025 took til Sep 17th. 1976 didn’t have one that later became a TS til the TD that formed on 9/26 and that became TS Gloria on 9/27. And there was a ST storm on Sept 13th. So, that doesn’t count as a TC. However, 1976 also had 2 TCs that maxed out as only TDs early in Sep. in the satellite era. So, even if a TD is declared today, 2026 has already beaten 2025 for the latest 1st TC declared in Sept. during the satellite era. Now, if it becomes a TS, that would mean that 1976 would remain the season with the latest first named TS in Sept. in the satellite era, which is Sept 27th.

This CFSv2 seasonal prediction site, which includes the ENSO SSTa forecasts, hasn’t updated in over 4 days: https://www.cpc.ncep.noaa.gov/products/CFSv2/CFSv2seasonal.shtml This is the most recent 10 day mean forecast for RONI: this has a peak at +2.9, compares to peaks of ~+3.5 on some runs from late July, and was suggesting further drops in the peak being likely on later 10 day means due to most of the blue lines being lower than the red ones:

12Z UKMET is at least the 2nd full run with it as a TD but the prior run didn’t do so until hour 36 (tomorrow at 8AM EDT) before dissipating it 48 hrs later; this run has it already doing that as of 2PM EDT today and then moving very little and never becoming a TS prior to dissipating at hour 96: GLOBAL MODEL DATA TIME 1200UTC 18.09.2026 NEW TROPICAL CYCLONE FORECAST TO DEVELOP AFTER 6 HOURS FORECAST POSITION AT T+ 6 : 31.9N 34.2W LEAD CENTRAL MAXIMUM WIND VERIFYING TIME TIME POSITION PRESSURE (MB) SPEED (KNOTS) -------------- ---- -------- ------------- ------------- 0000UTC 19.09.2026 12 32.2N 33.6W 1016 20 1200UTC 19.09.2026 24 32.7N 33.2W 1014 22 0000UTC 20.09.2026 36 33.1N 33.4W 1015 22 1200UTC 20.09.2026 48 33.8N 32.9W 1014 27 0000UTC 21.09.2026 60 35.0N 32.6W 1014 25 1200UTC 21.09.2026 72 34.5N 31.9W 1015 27 0000UTC 22.09.2026 84 33.5N 32.7W 1017 25 1200UTC 22.09.2026 96 CEASED TRACKING

The SOI has been negative for 37 days in a row.

The area near the Azores is now Invest 99L.

Something may be forming near the Azores: From 8AM TWO: Eastern Subtropical Atlantic: A trough of low pressure located several hundred miles southwest of the Azores is producing showers and thunderstorms that are showing some signs of organization. Environmental conditions appear marginally favorable for additional development over the next couple of days while the system moves slowly over the eastern portion of the Subtropical Atlantic. By early next week, environmental conditions are forecast to become less favorable for development. * Formation chance through 48 hours...low...20 percent. * Formation chance through 7 days...low...30 percent.

The AAM is now up to +3.7 and has a good chance to be off the chart tomorrow!

The mean global AAM based on this is not much above 0…+0.5 at most, not at all jibing with the Sep 17th +3.3. I don’t get it.

Indeed, the weighted avg of your graph, which looks like it is only ~+1.25 to 1.5, doesn’t at all jibe with the image below, which shows it ~+3.3:

12Z UKMET: again says no Gulf TC

It still does have a system / vorticity breaking off of the CAG 130'ish hours into the 6Z run, it just fails to develop a fully fledged TC and bring that into the GOM. That could just as easily come back on the 12z today. Again, chaotic. Though, yes, it also breaks off vorticity and develops a hurricane late in the run. Meh, these simulations will remain complete choas until something actually resolves. If anything can be taken from these runs at this point, it's to say we should have a warbling surface trough gyre establish itself by this weekend over central America and we just need to watch for any pieces of energy and vorticity that may break off on either side of the landmass (EPAC or WCARIB) for potential development over the next few weeks. The MJO is heading toward favorable phases for TCG at this time of year, which Joe Bastardi has been appropriately emphasizing in his call for activity:

Despite the Euro having something in the Gulf late, ironically the crazy GFS has no Gulf TC on its 6Z for the 1st run since way back at 18Z of 9/14! It just has one moving just N of Cuba (not in Gulf) at 384.

The off again, on again UKMET is now off again with a Gulf TC fwiw.

5th CFSv2 AAM run in a row with an extreme/historic level of 4+ being progged starting Sep 19th! It looks like it’s going to actually happen, folks! My inner weenie is genuinely excited: