La Niña now per NWS, but can we expect much more development to bring us above normal?

The latest enso forecast (IRI Columbia) dynamic avg puts at -0.71 C for OND….

2000, 2016, 2021 look to the the closest most relevant years.. but only 2016’s Hurricane Otto (which was an outlier all by itself) generated any significant ACE in November (About 8 ACE late November before crossing into the EP)

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Looking at OFCL and HCCA about 9-12 more ACE seems to be expected but this may be optimistic it seems to me… (currently at 93.2 ACE, so this should put us over 100 ACE if Jerry survives the shearing it will continue to undergo…. I did anticipate incorrectly we would be a bit over 100ACE a couple weeks ago with Humberto and Imelda, but both became extratropical well before originally forecast). In any case we should be around 100 ACE or a bit more within a week.

Last CPC outlook from a couple days ago shows some development chances around a CAG developing and some chances for a system developing from the MDR it approaches the Caribbean

Looking at google 06Z today (00Z shows something similar but less tracks in it heading into the Caribbean), I can see quite a bit more support than I last looked for such a MDR system beyond the next 7 days (17-21st of Oct) (I do recall it did also have a signal for Jerry’s development way beyond the usual 7 day window); not much support in next couple weeks for anything in Central America..

Per GFS/00Z looking at tropical tidbits, a wave is forecast to come off Africa over the next day however that particular wave only has little support (10% or less about).

However. Another wave is forecast to come off in 3-4 days that will have very slow development as a subtropical ridge develops north of it, leaving it fairly dry for a while as the AEJ will be moderate.. the ridge looks like it will be influenced by the remnants of Jerry as it passes by north of it — so there is one other obvious reason to not have high confidence in this solution… the model shows winds should pick up after a few days and increase its chances to develop though.

Based on google 06Z an optimistic chance of development this far out would put it at 40-50% for a TS and perhaps 20-30% for a hurricane, but it’s still very far out … Far out enough to not know even if it develops whether it will be steered into the Caribbean, curve NW as it approaches the Leeward Islands, or recurve fairly early. Barring an ideal scenario for developing ACE ( a long running track through the Caribbean like Beryl or another Humberto — highest ACE was 26 among the members ) it seems a bit unlikely but not impossible at the moment for such a single system to bring us the 26 ACE or so to bring us above normal (4 is the median for the incomplete tracks, with 8 the mean, so 10-20 would seem optimistic through the 21st of Oct.). That leaves about 5 weeks afterwards to generate anywhere from 5-20 ACE the necessary amount.

The 1991-2020 climo for Oct 22 to Nov 30 suggests about 12 more ACE for that time. So with an expected ACE of about 4 from the mean of a future Karen through Oct 21. And at least another 12 ACE that might plausibly come from the GoM or Caribbean from a different storm or two, that puts us at about at least 100+4+12= 116 ACE. If Jerry develops as expected that would bring us to less than 10 ACE from above normal. We would need a fairly active end of October or November to bring us to above normal, but we should expect a slightly more active end to the season given we are in a La Niña now, all other things being equal, as we should expect shear to be less of a limiting factor. Given the ample amount of OHC left in the likely areas for genesis it’s still possible for an above normal season (albeit it seems less likely at this moment).

NHC has downgraded Jerry's forecast twice in last couple advisories, and updated when they think it will become post-tropical.

At 94.4 ACE as of 06Z per colostate..

A quick manual calculation from the latest advisory, where I put it as post-tropical at 14/00Z yields another 3.31 ACE:

>>> x = [45, 45, 45, 45, 50, 50, 50, 50, 50, 50, 50, 50, 50, 50]

>>> np.sum(np.pow(x, 2)) / 1e4

np.float64(3.31)

The new Subtropical Storm Karen is forecast to become post-tropical tonight, should add another ~ 0.3 ACE on top of that based on the latest advisory.

This ields about 3.6 ACE, or 98 ACE after these two systems finish.

Google 00Z (40% a TS, 28% hurricane), and 06Z (38% a TS, 26% a hurricane) has dropped the chances of a previously mentioned MDR system down a bit, however the mean ACE though is now 12.9 for 06Z (so an expected 4.6 ACE still seems plausible based on that 36% chance).

98+4+12 = 114 ACE would seem to be expected, a bit less plausible then yesterday when we were 10 ACE away, now we are 12 ACE away from 126 ...

Should note, for 06Z there are some seemingly implausibly strong members (this would break a record I think) near the end of the forecast period for those members that make it into the Caribbean (the OHC is very high there though)..

ensemble_agg_max:

storm_ace (10^-4): 33.0

storm_vmax10m (kts): 177.9

sst_mean (C): 30.2

sst_min (C): 29.7

sst_max (C): 31.0

ohc_mean (kJ * cm^-2): 122.3

ohc_min (kJ * cm^-2): 84.1

ohc_max (kJ * cm^-2): 174.3

We are at 96.2 ACE now that Jerry and Karen are finished, and needing another 30ACE seems like a large ask, yet we have 1-2 systems left with chances for October in the models.

If AL97 becomes Lorenzo, it will add a tiny bit of ACE (1-2 ACE?), but the other system previously mentioned has been having a probability that has been shrinking in Google runs but still has decent chances in the EPS/00Z run (50%). I noted the Google 06Z run had another ~40 ACE outlier, with a median/mean of 12 when conditionalizing on the tracks that do form). Even if it provides half of that, an additional GoM / Caribbean hurricane in late October/November could put us over as mentioned previously.

Downbetting again a below normal season:

Currently at 49.8 ACE, and Gabrielle should bring 5-15 more ACE (hard to tell when it will become post-tropical/extra-tropical) with some very rough estimates (mixing NHC/HCCA/Google).

93L and 94L each both have roughly at least a 90% chance of becoming a TS each (based on FSU's chances of a TC (which will likely become a TS with the high SSTs), and the Google 23/06Z run (which essentially all of its members show a TS in the next 7-8 days).

I get ~14 ACE and 9 ACE respectively from the mean from google's tracks.

So, estimating the expected ACE from these 3 systems (taking the most conservative Gabrielle ACE value of 5):

5 + 0.9*13.7 + 0.9*8.7 = 25.16 ACE is the amount of expected ACE I would expect from these 3 systems.

This should takes us above a below normal season.

https://tropical.colostate.edu/Forecast/2025_0909_seasondiscussion.pdf

@SaviorofPlant Good report. Most surprising was the low vertical wind shear anomaly:

"Current 30-day-averaged zonal vertical wind shear is the 2nd lowest on record across the western Atlantic (10–20°N, 85– 50°W) (Figure 22)."

CPC has also issued their forecast today.

https://www.cpc.ncep.noaa.gov/products/precip/CWlink/ghaz/index.php

Estimating from CSU+Interpolated Consensus tracks, Erin is forecast to reach Cat. 5 soon and so should add something in the neighborhood of 40 ACE by the time its done, bringing us close to 50 ACE by August 24 (which is ~ 2x the 1991-2020 climatology)

new CSU forecast today puts expected ACE at 140 (drop from 155 last month).

Strong Caribbean shear for June, July is given as main reason in a post to X.

Doesn't seem like the sea temperature configuration is particularly favorable for activity this year but I am predicting above average again because that always seems to happen regardless