GaWx

I just found Sept 2M forecasts for Dec and Jan individually though not Sept for DJF: https://charts.ecmwf.int/products/seasonal_system5_standard_2mtm?area=NAME&base_time=202509010000&stats=ensm&valid_time=202510020000 @donsutherland1@mitchnick

In addition: The last few GEFS and EPS runs have forecasted MJO in the relatively favorable phases of 2, 1, and 8 through Sept. 19 and this would probably extend at least through the rest of Sept per longer term model guidance and climo:

Do you or does anyone else have a link that can be provided to past years’ Euro Sept 2m temperature forecasts going back however far they do for the respective upcoming DJFs for North America or the US? Edit: I found it kind of sort of. See post below. @donsutherland1@mitchnick

The new Euro has DJF Nino 3.4 much cooler than last month with it at ~-0.50 vs last month’s -0.08: 8/1/25 Euro prog for DJF: -0.08 9/1/25 Euro prog for DJF: ~-0.50

The last few GEFS and EPS runs have forecasted MJO in the relatively favorable phases of 2, 1, and 8 through Sept. 19 and this would probably extend through at least the rest of Sept per longer term model guidance and climo:

Thanks, Don. As I assume you realize, crop sizes have overall so far actually been aided rather than hurt by increased CO2: -GW has lead to longer average growing seasons thus increasing avg crop sizes. -Related to this, the increase in avg growing season lengths has allowed crops to be grown further north than in the past. -There’s now increased CO2 for plants to thrive better (the “CO2 fertilization effect”). -At least partially related to this improved environment, the Midwest has had a decrease in the frequency of widespread droughts since the 1990s. Thus, I suspect that one of the reasons that CC isn’t being treated as a major crisis by as many as you’d want is that it has actually lead to more favorable rather than less favorable conditions for food supply, one of the biggest essentials to support animal life. That’s a huge benefit for life on our planet. So CC, though very bad for rising sea level, increased frequency and severity of major flooding events, increased frequency of severe TCs, increased coral bleaching, and an increase in extreme heat related casualties, hasn’t been all bad news by any means. To minimize the major benefit to food supply as well as a decline in extreme cold related casualties would not be considering the full effect of CC.

Nobody knows, which is what makes forecasting discussions so interesting. For comparison purposes, here are some very quiet periods during climo active dates of other non-El Nino seasons during the current active era: -In 2024, there were 0 TCs during the 19 days 8/21-9/8. -In 2022, there were 0 TCs in August. -In 2016, there were 0 TCs Sep 4-11 and 0 H Sep 3-28. -In 2013, there was no H til 9/11. -In 2001, there was no H til 9/8 ———- Back to 91L: 12Z Euro has no TC from this in the MDR although something forms later in the subtropics. So, the highly unreliable JMA, especially when it’s on its own, is the line holdout of this cycle for a TC in the tropics from this. Edit: For record-keeping purposes now that the rest of the run has been released, the 12Z JMA is a bit slower than the prior two. But it still has a similar idea of an early recurve with a H moving N along 60W 144-192.

12Z rundown so far: Icon and GFS have almost nothing unlike recent runs. CMC is so far (through 78) coming in much weaker with no closed LLC. UKMET once again has no TC. Edit: But fwiw JMA still has it in the MDR at 72 (1008 mb TC):

Indeed, Mitch! Check out this poor CANSIPS ENSO verification: 8/31/24 run for Aug ‘25 had Modoki Niño look 7/31/25 run for Aug ‘25 asks “what Modoki Nino?”

It’s very hard to predict with confidence how the upcoming winter will be this far out. But I will say that pretty close to normal temperatures (based on 1991-2020 averages) in your area (NE US) are quite possible this DJF.

Thanks. Over the longer term and including all months, ~40% of TCs passing near the Virgin Islands later hit the Conus. The % is probably highest in Jul/Aug/first half of Sept.

From something well to the W of 91L coming out of the Caribbean in 6-7 days, the 6Z GEFS is pretty active mainly in the Gulf with a couple E of FL. Some of these members are hurricanes. *Edit: The GEFS/EPS of the last few days have had the MJO then in or near the most dangerous phase for July-Sept CONUS H hits, phase 2: Edit: 6Z GEFS suggests there could be another TC coming out of the W Caribbean later.

1. 0Z Euro has no TC from this. That weak low into CHS late is home-grown. 2. 6Z GFS is way OTS, even E of Bermuda. 3. 6Z Icon is much weaker at the Lesser Antilles at 120.

0Z: -The UKMET is again too weak with the low to classify it as a TD. -The 0Z CMC is similar to the GFS in being further S than its prior run and is close to the 0Z GFS as of 144.

The Gulf storm and the storm ahead of Invest 91L/likely future Gabby may end up being one and the same for all we know now.

For the record, today’s 12Z JMA moves much more quickly as it gets near Bermuda at 192! What’s up with that? This is actually consistent with yesterday’s 12Z JMA.

They’re ensemble members. They don’t depict them with names.

990s-950s/TS to cat 3

Yeah, ones in Gulf may very well be from MDR AEW ahead of 91L.

Check this out from the Happy Hour GEFS: I don’t think that any of these are from Invest 91L, but I’m not saying it’s drunk either. I think these are from a legit system ahead of 91L. Are they from the system between 45W and 50W?

The 12Z EPS has one member from 91L hit FL, another headed toward the Gulf, and a couple of others not far from hitting the NE US as they recurve. But overall, that’s still pretty quiet for CONUS. Interestingly, there’s more Conus hits from other systems, mainly homegrown stuff.

Hey Manda, Your posts are appreciated but please go here for discussion devoted to Invest 91L:

12Z: -Euro: has a TS in the MDR that later weakens to a weak low as it crosses the Lesser Antilles and then goes through Caribbean disorganized/very weak -UKMET: no TC again/low too weak to be classified a TD

RONI-ONI differences have been slowly dropping since late in 2024 and especially since FMA: 2024: JJA -0.54 JAS -0.52 ASO -0.54 SON -0.55 OND -0.55 NDJ -0.54 DJF -0.53 2025: JFM -0.51 FMA -0.49 MAM -0.43 AMJ -0.38 MJJ -0.32 JJA -0.29