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Casuarina Head
Member
The CS3 composite for March 2024 has been released. Its breakdown for August, SST-wise, is as follows:
C3S (Aug 2024): eight models
Subtropics > MDR: 0
MDR > subtropics: 4 (DWD, ECMWF, JMA, ECCC)
Subtropics = MDR: 4 (CMCC, UKMO, CFS, Météo-France)
So there is an even split between the models that a) show a warmer tropical vs. subtropical Atlantic and b) those that depict basin-wide warmth. The former setup would favour an extremely active season, given the favourable variables elsewhere, but the latter would not. The latter, in particular, would imply stability and/or wave-breaking (TUTTs = periodic shear) over the tropical Atlantic, as has been often seen in many recent seasons, preventing higher-end outcomes. If the first subset were correct, then 2024 would likely have a chance to be “hyperactive,” ACE-wise. If not, then I would expect slightly-above-average ACE, in line with a “typical” above-average season. Currently I am being conservative and strongly favouring the “above-average-but-not-hyperactive” camp.
Casuarina Head
Member
The latest UKMET run shows a rather significant shift toward a somewhat cooler MDR and a much warmer subtropical region. Perhaps some of this is due to the fact that global models are showing a more persistent +NAO during this timeframe vs. previous runs, which certainly is not going to increase the odds of a hyperactive season. Also note that there is a slight cool anomaly to the south of the southern tip of Greenland that should not normally be present in a canonical +AMO. All in all, given these trends, I think that 2024 will struggle with shear and stability during its peak months, -ENSO and the trend away from a +PMM notwithstanding. 2020 featured a similarly favourable setup in the Pacific yet barely managed to break the threshold of hyperactivity.
By contrast, here is the composite SST anomaly for all the hyperactive seasons since the most recent +AMO began. Note that the relative cool spot south of southern Greenland is either less defined than forecast by the UKMET or otherwise absent altogether, while most of the Labrador Sea, along with the Eastern Seaboard and Gulf of Mexico, is cooler. At this point I think that getting solid hyperactive years is going to be harder in a warming world, as the polar region and the larger oceanic basins are warming up faster than the tropical Atlantic. Owing to this, lots of stability and TUTTs will likely prevent multiple long-tracked, high-ACE major hurricanes from forming between Africa and the Lesser Antilles, making 2004- or 2017-type setups less common than in the past.
By contrast, here is the composite SST anomaly for all the hyperactive seasons since the most recent +AMO began. Note that the relative cool spot south of southern Greenland is either less defined than forecast by the UKMET or otherwise absent altogether, while most of the Labrador Sea, along with the Eastern Seaboard and Gulf of Mexico, is cooler. At this point I think that getting solid hyperactive years is going to be harder in a warming world, as the polar region and the larger oceanic basins are warming up faster than the tropical Atlantic. Owing to this, lots of stability and TUTTs will likely prevent multiple long-tracked, high-ACE major hurricanes from forming between Africa and the Lesser Antilles, making 2004- or 2017-type setups less common than in the past.
Highly doubt it will amount of anything but...
What is this?
Tweet from someone who said there was a very, very small chance of a subtropical storm forming.
I remember seeing something about this and I was talking about on Discord.
CSU's forecast is now out. CSU's five analogs for the 2024 Atlantic seasonal forecast are: 1878, 1926, 1998, 2010, and 2020. Analogs are selected based on likely La Nina and above-normal sea surface temperatures in tropical Atlantic for August-October.
Casuarina Head
Member
All the high-ACE forecasts are, in my view, going to bust very badly. (In particular, all of CSU’s previous calls for ACE of > 160 units ended up verifying much lower than expected.) The most recent dynamical modelling shows a stronger Newfoundland warm pool, and a warmer subtropical North Atlantic, along with a weaker +AMO compared to that on previous runs. This implies that stability and shear will be an issue once more, as the warmest +SST anomalies will be north of the deep tropics during the peak of the season. Merely having well-above-average MDR temperatures will not be enough to ensure hyperactivity, even with La Niña, if the preponderance of the warmth is up near the Canadian Maritimes. I think that actual ACE units will end up somewhere in the 140s, but not much higher, if at all. That would still be above average, however, but in no way hyperactive. The “hurricane season from Hell,” to paraphrase AccuWeather, most likely won’t be, at least ACE-wise (landfalls could always be another story, but historically, most U.S. major landfalls originated between Africa and the Lesser Antilles, if I recall correctly).
TWC Outlook:
Casuarina Head
Member
^ This is the kind of SSTA configuration that would need to persist through the peak of the season, in order to favour the upper-tier ACE forecasts. However, the preponderance of the dynamical guidance currently seems to favour considerable warming of the subtropical Atlantic over the coming months, which, in my view, would likely lead to the “bust” that was mentioned previously.
At this stage I will only believe the “hyperactive” forecasts if SST anomalies look like this in late July or early August. Given climate change I will be rather shocked if a big Newfoundland warm pool somehow does not reemerge just in time for the peak of the season. At this point I still would expect this to prevent seasonal ACE north of the 140s, let alone the 190+ units (with CV long-trackers à la 2004/‘17) that a lot of sources seem to anticipate.
This and the upcoming seasons will have a lot of ground to cover in order to make up for high-end U.S.-landfall deficits vs. previous +AMO cycles. Even the last -AMO seemingly produced more-frequent Cat-4+ hits that were verified by ground-based observations. 2024 alone will probably need multiple Carla- or 1926-style hits on eastern peninsular FL and/or TX, in order to allow subsequent years to catch up. But will climate allow this?