LarryWx wrote:Category5Kaiju wrote:Personally I'm quite interested to see what October and November will produce. While it's definitely not something I'd expect by default, it's also intriguing to think back at -ENSO seasons such as 1998, 1999, 2005, 2008, and 2020. Back during those Septembers, who would've thought that a destructive Category 4 or higher hurricane would've formed during the late months? And, in the extreme case of 1932, a November Category 5 hurricane?
2025's story has been tame so far. But will it be like this the next 70 days?
As always, I’m also quite interested. I continue to fear what these late periods are capable of producing based especially on the recent past. Having 3 of the 7 most active Oct-Dec periods ACEwise (70+) during just the last 9 seasons is not comforting at all. Moreover, 3 of the last 6 (50%) La Niña seasons (2024 per RONI counts as La Niña) were in these top 7!
The one somewhat comforting thing, however, is the relative slowness of 2025 so far and how that affects the chances for a highly active Oct-Dec. There appears to be some correlation between how active a season is prior to Oct and how active is a season Oct-Dec, which means that having a relatively slow season through Sep does appear to reduce the chance for a very active Oct-Dec (50+ ACE) somewhat vs that chance when pre-Oct isn’t slow:
Seasons with 50+ ACE during Oct-Dec:
Year/pre-Oct ACE/Oct+ ACE
2024: 78/84
2020: 106/75
2016: 59/80
2005: 171/75
1969: 93/57
1963: 49/63
1961: 134/55
1950: 157/54
1932: 87/82
1894: 59/76
1893: 159/73
1887: 123/59
1878: 84/97
Per this list based on each era’s normal ACE, the pre Oct ACE for these 13 very active Oct-Dec was as follows:
- 6 MA normal (2005, 1961, 1950, 1893, 1887, 1878)
- 3 AN (2020, 1969, 1932)
- 1 NN (1894)
- 3 BN (2024, 2016, 1963)
So, 50+ Oct-Dec years have been heavily biased toward pre-Octs that were active.
Where is 2025 headed for pre-Oct? Through Gabrielle, the prog is for ~~55. Then there’s the current MDR orange. The consensus has this as TS Humberto by 9/26-7 and a H soon after. That would have a realistic potential of 10-15 ACE 9/26-30. So, that would get total 2025 pre-Oct ACE to as much as ~65-70. That compares to 94 for the 1991-2020 pre-Oct avg, which means 2025 pre-Oct will end up solidly BN just about regardless of what Gabrielle and Humberto do.
What does this tell me? With 2025 almost definitely headed for BN pre-Oct, the chance for a 50+ Oct-Dec is <50%. However, 2024, 2016, and 1963 as well as 3 of the most active 7 Oct-Dec on record having occurred just within the last 6 La Niña seasons also say don’t bet the farm on <50 for Oct-Dec at least as of yet.
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!
