2025 Indicators: SST's, MSLP, Shear, SAL, Steering, Instability (Day 16+ Climate Models)

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Teban54
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Re: 2025 Indicators: SST's, MSLP, Shear, SAL, Steering, Instability (Day 16+ Climate Models)

#401 Postby Teban54 » Fri Jul 11, 2025 1:51 pm

There were a lot of discussions last season, particularly during the anomalously quiet September, about the ITCZ position being too far north. To recap, this is how 2024 looked like. Red is west region (10W to 10E), and Blue is east region (20E to 35E).

Image
Image

2024's eastern ITCZ started running significantly north of average in late June, which persisted during the entire hurricane season. The western ITCZ was also northward-displaced during September and October, the peak MDR season.

While this northward-displaced ITCZ resulted in anomalously early and late MDR hurricanes (Beryl, Kirk, Leslie), it was generally believed to have contributed to a surprisingly quiet peak season: waves were too far north when entering the Atlantic, and entrenched too much dry air from the Sahara even while still in Africa.

So how does 2025 look?

Image

Image

Curiously, while the eastern ITCZ had been south of normal earlier this year, it rose to climo latitude during the first 10 days of July. (The western ITCZ has been mostly near-normal, but IIRC, people thought that the eastern ITCZ was more impactful.)

Note that ITCZ position itself isn't the sole contributor of wave position, dry air and "wave-breaking":
  • 2022: North displaced during September, but largely normal during the storm-free August.
  • 2021 (table only): The season had notable MDR activity (Larry, Sam), much beyond what SSTAs and other indicators would predict, which is often attributed to a strong Atlantic Nino. ITCZ data is hard to read, but looks like the western and eastern halves were south-displaced at different times of the peak season. This may have contributed to storms consistently forming at low latitudes during most of it (Fred, Grace,
  • 2020: Another "odd" hyperactive year with many MDR storms struggling (other than Teddy). ITCZ was very north-displaced in August, possibly resulting in Laura cutting right through the Greater Antilles. But it was fairly normal (with western ITCZ even south of climo) in mid-September when the CV parade happened, yet the storms still formed too far north. So ITCZ isn't the main culprit.
As for what the future holds, I don't know.
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Re: 2025 Indicators: SST's, MSLP, Shear, SAL, Steering, Instability (Day 16+ Climate Models)

#402 Postby LarryWx » Sat Jul 12, 2025 1:34 pm

-2025’s 1.46 is 52nd of the last 75 seasons ACEwise as of July 12th

-The last season with 7/12 ACE lower was 2009’s 0

-But 2004, 1998, 1985, 1969, and 1955 also had 0 in addition to 11 others

-The predictive value of 7/12 ACE for the remainder of season’s ACE is virtually 0

-Here’s the 7/12 ACE position out of 74 for seasons with 150+ ACE remainder of season: 2nd, 6th, 14th, 17th, 18th, 24th, 31st, 34th, 59th-61st, 66th

-So, avg 7/12 position of seasons with 150+ ACE to follow: 33rd of 74
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Re: 2025 Indicators: SST's, MSLP, Shear, SAL, Steering, Instability (Day 16+ Climate Models)

#403 Postby cycloneye » Sun Jul 13, 2025 5:48 am

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Re: 2025 Indicators: SST's, MSLP, Shear, SAL, Steering, Instability (Day 16+ Climate Models)

#404 Postby WeatherBoy2000 » Sun Jul 13, 2025 10:56 am



Eric Webb is still skeptical about an active Atlantic hurricane season, despite the recent warming and predicted weakening shear:

 https://x.com/webberweather/status/1944403735431577730



 https://x.com/webberweather/status/1944420258518876668



He points out that the climate models have done poorly in seeing the high shear in the tropical Atlantic so far and thinks that will largely continue, despite some temporary reprieves. Imo whether he ends up mostly right or wrong is going to be down to if the tropical Atlantic stops warming and that the enso doesn't notably cool off as predicted. It would be one thing to be more confident in this prediction if there were an actual el nino in place, but there isn't, so the overall shear pattern is probably more susceptible to change.
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Re: 2025 Indicators: SST's, MSLP, Shear, SAL, Steering, Instability (Day 16+ Climate Models)

#405 Postby Category5Kaiju » Sun Jul 13, 2025 11:10 am

WeatherBoy2000 wrote:


Eric Webb is still skeptical about an active Atlantic hurricane season, despite the recent warming and predicted weakening shear:

 https://x.com/webberweather/status/1944403735431577730



 https://x.com/webberweather/status/1944420258518876668



He points out that the climate models have done poorly in seeing the high shear in the tropical Atlantic so far and thinks that will largely continue, despite some temporary reprieves. Imo whether he ends up mostly right or wrong is going to be down to if the tropical Atlantic stops warming and that the enso doesn't notably cool off as predicted. It would be one thing to be more confident in this prediction if there were an actual el nino in place, but there isn't, so the overall shear pattern is probably more susceptible to change.


Don't get me wrong. I love Eric Webb's analyses and really respect him as a scientist. However, I do think that in this particular case, he might leaning a *little* bit too much into extrapolating what has happened recently to what will happen months down the line. I'd love to know how these models fared in recent years, as that may give us a good barometer for what to expect and what has transpired before.

Wind shear, wind shear, wind shear. Great for tornadoes, bad for hurricanes. If there's anything about wind shear that I think is worth hammering down, it's that it's extremely volatile. Who knew that Delta would've been knocked down just after RIing into a Category 4 because of shear? Oh yeah, and remember that time when we saw the forecast for elevated shear across the Atlantic on August 31, 2019, based on model outputs on August 1, 2019? Danny may be right here, sometimes the broader picture (lowering of wind shear, no El Nino) may be the better answer to our questions.
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Re: 2025 Indicators: SST's, MSLP, Shear, SAL, Steering, Instability (Day 16+ Climate Models)

#406 Postby weeniepatrol » Mon Jul 14, 2025 1:52 pm

Agreed… we know vertical shear will become more favorable because the TUTT and easterly trades weaken through August. I’m not convinced. Maybe the broader area-averaged mean of the entire tropics exhibits above average shear, but it seems likely that at least a couple systems are going to find a window of “good enough” to develop.
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Re: 2025 Indicators: SST's, MSLP, Shear, SAL, Steering, Instability (Day 16+ Climate Models)

#407 Postby weeniepatrol » Mon Jul 14, 2025 1:55 pm

Speaking of TUTT, check out this well-defined, textbook example of one.





You can even readily see the upper convergence at the base of the trough through the void on water vapor.
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