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2024 Atlantic Hurricane Season

JPWX

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Personally, at this point I think that legit hyperactivity is still questionable, let alone an ACE index of ≥ 190. Back in 2022 CSU forecast five majors and a seasonal ACE value of 180, yet only a pair of majors formed and ACE was well under the “hyperactive” threshold of ~160. Last year the updated UK Met Office forecast on 1 August called for six majors and an ACE value of 215 (actual total: ~146 at most). Plus, as mentioned previously, over the past few decades I suspect that storms’ peak intensities have been inflated, so the “true” ACE would have been lower than officially listed in some years. If the Newfoundland warm pool persists, I think that ACE, while above average, will still be well below true hyperactivity, and possibly even lower if La Niña fails to develop as quickly as some modelling suggests.
 
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I’m seeing a lot of chatter elsewhere (i.e., on Twitter/X) about how warm the (tropical) Atlantic is right now relative to average. People are talking about how SSTs are running ahead of 2010 to date, how warm the entire basin is, etc. The thing is, while the deep tropics, being well above average, are ahead of 2010, so too are the subtropics. The Sargasso Sea and the Atlantic Seaboard this month are much warmer than they were in the first week of February 2010. Everywhere is warmer.

The widespread, basin-wide warmth means less of a temperature-gradient between the polar region and the tropical Atlantic. By itself this would actually tend to suppress ACE, given that fewer intense storms are needed to redistribute heat in a warmer world. Simply put: massive warmth does not necessarily imply higher ACE, and given context may actually indicate the opposite. (Bear in mind that 2010’s seasonal ACE was ~165, barely “hyperactive,” despite record warmth and -ENSO.)

All else being equal: a much warmer MDR + much warmer subtropical Atlantic vs. 2010 would suggest similar or lower ACE, all else being equal. I think that calls for 200+ units of ACE and another 2005-/‘17-type season are overdrawn at this point. I don’t think that the long-trackers are necessarily returning to the same extent seen in past “hyperactive” seasons such as the aforementioned, simply because the extent of the warmth means less of a need for high-ACE storms.
 
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ACE180plus.png


^ Two select subsets of a) years with seasonal ACE ≥ 180 units (left) and b) ≤ 180 units (right). Note that, based on the difference(s) between the two subsets, the top-tier years tended to feature stronger cold (-) SST anomalies in the subtropics (up to -1.0) than positive (+) in the deep tropics (up to +0.4). Currently 2024 is featuring warmer SSTs in the subtropics than 2010 did at the same time, despite also being warmer in the deep tropics. This seems to be more in line with the seasons that featured seasonal ACE of less than 180 (and often less than 160). So at this point I remain skeptical that 2024 will be more intense ACE-wise than 2010.
 
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•MAJOR HURRICANES: 5-12 (MY FORECAST MADE ON OCTOBER 1ST, 2023)
•TOTAL ACE: 190 TO 230 RANGE (MY FORECAST MADE ON OCTOBER 1ST, 2023)
Since the start of the most recent +AMO, four seasons—1996, 2008, and 2010—each featured at least five majors—including long-trackers such as the two Berthas, Edouard, Fran, Gert, Danielle, Ike, Earl, and Igor—yet seasonal ACE of ~165 units or fewer. (1999 also featured five majors but a higher ACE of ~175 units.) A seasonal ACE of at least ~190 units since the start of satellites in 1960 has only occurred five times: in 1961, 1995, 2004, 2005, and 2017. As for a dozen majors: the record number for the Atlantic is seven or so. Over the past few seasons there were some models and/or agencies (ECMWF, UKMET, University of Arizona) that called for similar ACE to your values, some as late as August, but ended up verifying poorly. If we get a “hyperactive” or near-“hyperactive” season in 2024, something like 2008/‘10 would seem to be more likely than a top-tier exception like 2005/‘17.
 
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^ Note the rather strong correlation between strong +AMO/-ENSO combinations and record-breaking “hyperactive” ACE (implied by high hurricane totals). 2024 may well see record-breaking SSTs in the deep tropics (indeed it already is, albeit only back to 1981), alongside a fairly robust Niña in the Pacific. However, the combination of a +PMM—meaning warmer SST north of the equatorial Pacific, hence higher-than-expected EPAC TC activity—and persistent warmth in the subtropical Atlantic, off Newfoundland, may well offset an otherwise-favourable setup, resulting in much lower ACE than might be inferred. I suspect that lingering stability and shear will limit ACE, given the +PMM, climate change, and the aftereffects of El Niño.
 
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Note that the latest EC actually shows cooling in the MDR between March and April, along with comparatively-tame-but-still-above-average values by August. The latest run also shows a cooler North Atlantic off of Greenland from March through May vs. the preceding run, which would be less favourable for significant ACE in the deep tropics, signifying as it would less of a +AMO. I could be wrong about this, of course, but in the end seasonal ACE may not be too far from last year’s, i.e., in the 140s or so, rather than (near-)record-breaking or even “hyperactive.” Come back in November and compare some of the preseason talk about 1933 etc. and I think some people will be surprised. We shall see.
 
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Global models are showing a persistent +NAO during the next few weeks, along with strong easterlies over the +AMO “horseshoe.” I would not be surprised if the record-breaking SST anomalies in the tropical Atlantic were to cool significantly, perhaps falling back in line with long-term averages. Models suggest that the +NAO may persist through early March at least. If I were to make an early guess as to the season, I would, preliminarily, side with numbers similar to those of the past few seasons: around fifteen named storms, five hurricanes, and three majors, along with an ACE of ~120 to 145. I suspect that the more aggressive forecasts, be they professionally issued or not, are going to be grossly overestimated, but of course, I could be wrong.
 
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202420-Feb-OISST.png


The most recent four days show the steepest post-onset decline since at least November of last year. Moreover, reliable modelling suggests that trades over the tropical Atlantic should peak over the coming week, and that weaker trades should return by early March. Such a duration of enhanced easterlies will enable further robust cooling during this timeframe. Given the recent magnitude, SST anomalies could soon be close to last December’s, effectively undoing much of the record-breaking warmth. Currently the cooling is matching or outpacing previous periods of warming, yet is getting less attention thus far than the warmth. The +NAO certainly appears to be working wonders, so to speak—in a good way.
 

JBishopwx

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Posted in the other thread, but I post it in here too....

Here is a link to the changes with more details: https://www.nhc.noaa.gov/pdf/NHC_New_Products_Updates_2024.pdf
-Expansion of Spanish products,
-Issuance of U.S. watches and warnings on Intermediate advisories:
- Extension of tropical storm (39 mph, 34 kt) and 58 mph, 50 kt)) wind radii forecasts to days 4 and 5:
-Weblinks in the Public Advisory:
-Change to the time zone reference in the eastern Pacific
-Experimental Cone Graphic with a depiction of inland watches and warnings for the United States
-Experimental international tropical cyclone rainfall graphics:
-New Marine Forecast Product “Offshore Waters Forecast for the southwestern North Atlantic Ocean
 

Atlantic

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This has trended though two concective GFS runs (06Z and 12Z) of today. Could we see a possiblity of Subtropical development between February 29th and March 7th? The area over the Bahamas is the second system after the first one that Mr. WeatherMan mentions in the video on the left that shows up on February 29th: Screenshot 2024-02-22 1.24.50 PM.png
 

JPWX

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This has trended though two concective GFS runs (06Z and 12Z) of today. Could we see a possiblity of Subtropical development between February 29th and March 7th? The area over the Bahamas is the second system after the first one that Mr. WeatherMan mentions in the video on the left that shows up on February 29th: View attachment 23975

Last tropical system in March was 1908.
 
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