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

[cycloneye]

 https://x.com/TylerJStanfield/status/1943013719514190123

[Category5Kaiju]

Let me preface things with this: I'm very willing to eat crow and own up to it if what I'm about to say is proven to be wrong in the end. However....I personally think that some of the speculations (especially on various wx social media posts online) that stability this year is going to be a major problem and detriment to overall Atlantic impacts/activity because of the warm subtropics are a *tad bit* overblown. Here's why I think that is the case.

Here's where we are now, sst anomaly configuation-wise:



Speaks for itself. Subtropics are much warmer than average. Deep tropics are somewhat warmer than average.


This is late August 2017:



Honestly, at least in the Atlantic, sort of similar to what we're seeing now. Warm deep tropics, cool band just to the north, and warm subtropics. Also, check out the very warm waters near Greenland, Iceland, and the UK.

Now, you would think that if it was as simple as warm subtropics robs deep tropics action, then that time period would've seen very little activity. However, check the date. This was what the Atlantic looked like between Harvey's devastating Texas landfall and Irma's birth. The true story is anything but quiet!


And now, late August 2022:


Now THIS...this is how you're going to get serious stability problems. The subtropics are INSANELY warmer than average, and the deep tropics are only somewhat warmer than average. This image of the Atlantic was around the notorious wavebreaking/mid-level dry air period when not a single named storm was able to form.


So...I guess my point here is, unless 2025 experiences as drastic as a warmup as 2022, especially with the subtropics/tropics sst anomaly discrepancy, then I'd have to imagine that stability would only go so far as to hamper the season. The long range models have their ideas, and we rightfully and obviously go off of them to make judgements. But...the facts present themselves as well. We already had 3 named storms (if wavebreaking/mid-level dry air was such an issue now, then I highly doubt we would've even seen named storms form), 2 of which ended up becoming impactful systems (Barry a weak but bona fide tropical-born system and Chantal a Carolinas tropical storm right at the cusp of what could've been a robust strengthening phase). Are the subtropics being anomalously warm really that big of a problem, at least as of recently?

[ScottNAtlanta]

I've been looking at the MJO forecasts
https://www.cpc.ncep.noaa.gov/products/ ... r_wh.shtml
I am noticing a pattern. Every season the MJO always seems to want to park on one side of the globe. The majority of the last several seasons it has tried to stay in the positive phases (8-3), but this year it seems to want to stay in phases 5 & 6 head to the nul phase and back around to 5,6, and 7. Those are unfavorable for Atlantic development. Of course there is always the home grown stuff, but it doesn't look like the MJO will be in favorable phases until possibly late August or September.

[DorkyMcDorkface]

I've been looking at the MJO forecasts
https://www.cpc.ncep.noaa.gov/products/ ... r_wh.shtml
I am noticing a pattern. Every season the MJO always seems to want to park on one side of the globe. The majority of the last several seasons it has tried to stay in the positive phases (8-3), but this year it seems to want to stay in phases 5 & 6 head to the nul phase and back around to 5,6, and 7. Those are unfavorable for Atlantic development. Of course there is always the home grown stuff, but it doesn't look like the MJO will be in favorable phases until possibly late August or September.

Fwiw EPS has it finally returning to a favorable phase the first half of August. I know in recent years we've mostly had to wait until the final two weeks of the month for activity, but I would assume this would open a potential window in the deep tropics around that timeframe.

Edit: would like to add this coincides with the ripping shear in the Caribbean lessening on the EPS as well.
[/img]

[WeatherBoy2000]

C3S is generally keeping with the more stable and drier theme for 2025, however, its prediction is nowhere near as dry as it was predicting for years like 2018, 2019, 2021 at this time:

 https://x.com/dmorris9661/status/1943291279456018516



Those were ultimately slightly to moderately above normal seasons.

[kevin]

The MDR has been rapidly warming during the last two weeks. On June 25, the MDR SST was the same as 1991 - 2020 climatology (26.76C, 0.00C anomaly). However, now the MDR SST is 27.33C, a +0.38C anomaly compared to climatology (26.95C). While this is still not close to anomalies we saw the last two years (+1.31C and +1.16C for 2023 and 2024, respectively) it's already getting close to the +0.60C value that f.e. 2020 had at this time of the year. Another two weeks of similar warming would already bring the MDR SST anomaly to the same level as in 2005 at the end of July. Not per se drawing comparisons to those hyperactive years, but it's just to say that, despite the late start of the warming, 2025 still definitely has a chance to have a very warm MDR. The North Atlantic is general is still the #3/#4 warmest on record (behind 2023, 2024 and roughly tied with 2010).

[DorkyMcDorkface]

C3S is generally keeping with the more stable and drier theme for 2025, however, its prediction is nowhere near as dry as it was predicting for years like 2018, 2019, 2021 at this time:

 https://x.com/dmorris9661/status/1943291279456018516



Those were ultimately slightly to moderately above normal seasons.

Yeah that was something I highlighted earlier, while this is not shaping up to be an upper-echelon season I still don't see how we wouldn't finish at least slightly above avg give those aforementioned seasons arguably had less favorable looks SST-wise up to this point (especially 2018 which had a near record-cool MDR), not to mention unlike 2018 and 2019 ENSO looks to remain negative (and has a chance to restrengthen into a full-blown Niña if the CPC is to be believed).

Not saying there won't be issues regarding elevated stability of course (especially seeing as that's been seemingly par for the course in recent years, particularly in August), but I find it difficult to believe we'll see less activity than any of those years.

[cycloneye]

@BenNollWeather
A convective pulse is forecast to move across the Atlantic into Africa during late July and early August, potentially bringing the season's first chance for a hurricane.


 https://x.com/BenNollWeather/status/1943328106795724975




@MichaelRLowry Definitely something to watch

 https://x.com/MichaelRLowry/status/1943333490659070365

[cycloneye]

Linked to the above post is the Ryan (WeatherTiger) message. Very interesting.

 https://x.com/wx_tiger/status/1943354178769973708

[cycloneye]

 https://x.com/WxTca/status/1943368885723443397



 https://x.com/WxTca/status/1943368893319237764

[USTropics]

This has been something I’ve wanted to do for a while now, and I thought this would be a fun educational/thought experiment where we can get everyone’s opinion and ideas on the data/observations and for any future implementations (especially during the Atlantic ‘preseason’ months ).

Essentially, we are going to use some of the same methods that CSU uses for their seasonal forecasts and apply them for each month (starting with May data). As stated above, I definitely want this to be an open conversation/discussion, so any thoughts/improvements/additions for future updates feel free to share them. If other people want the code to do this (all Python), I can also put something on Github for a more open collaboration. First, some of the more specific details on what we’re exactly doing here:

• We need data, so let’s use the NCEP/NCAR daily reanalysis dataset from PSL. This has the benefit of being one of the more accurate reanalysis datasets that is also current (~2 day lag time from current day) and has a ton of variables/parameters to look at (e.g., heights, sea surface temperatures, zonal winds, etc.). You can find their reanalysis data and other associated products here - https://psl.noaa.gov/data/index.html
• We need to identify a set of climatology years and get a mean value for those years. One limitation of our selected dataset is it only goes back to 1948, so we’ll be selecting the top 10 years in ACE from 1948 - current. That gives us the following 10 years: 1950, 1961, 1995, 1998, 1999, 2003, 2004, 2005, 2017, 2020
• We need to identify a time period and get an average value for each year. For this post, we are going to use all 31 days in May for each year to create a climatology dataset, then we will merge those 10 active years into a singular monthly dataset. We can then create an anomaly composite using that data.
• After this, we can identify certain departures of anomalies that appear during active years. This will make more sense later in the post, but I’ve loosely identified extent boxes and have given them labels for such areas.
• We’ll then apply these same techniques for May 2025, and see what differences or similarities appear from our active year extent boxes.

Now that all of that is out of the way, let’s get to the fun stuff!

Sea Surface Temperatures
The only reason we can even reasonably predict hurricane seasons with skill 3-4 months in advance is because our oceans are great at storing information (in the form of energy) for ‘longer’ periods of time (physics 101: water is a great conductor of heat, but air is poor at this). So let’s start there—here is the composite for top 10 active years for SSTAs and the May 2025 data.



In this analysis, I’ve identified key regions where major global ocean currents traverse and the associated sea surface temperature anomalies (SSTAs) that correlate with active Atlantic hurricane seasons. In addition to the ENSO region, these currents play a critical role in modulating SSTs, atmospheric circulation, and large-scale climate patterns.

++ Anomalies ++
Canary Current
Kuroshio Current

-- Anomalies --
Agulhas Current
Mozambique Current
Gulf Stream
ENSO Region

May is a transitional month when large-scale oceanic and atmospheric patterns begin to organize, setting the stage for the Atlantic hurricane season. Analysis reveals a strong correlation in May between the ENSO region and forecasting the intensity of the upcoming hurricane season. La Nina is a well-established driver of active Atlantic hurricane seasons, as it reduces vertical wind shear, warms MDR SSTs, and enhances the African monsoon. Negative SSTAs in May signal the onset or persistence of La Nina, which creates a low-shear, warm-SST environment in the Atlantic (especially in the later months).

For the Atlantic, the Canary Current (and not the MDR) having a warmer signal tends to equate to a more active hurricane season. This would make sense, as positive SSTAs in the Canary Current in May tend to propagate equatorward toward the MDR and eastern Atlantic by June–August, driven by ocean currents and atmospheric forcing.

Interestingly, a warmer Kuroshio Current equates strongly with an active Atlantic hurricane season. I believe the main correlation here is that warmer waters in the western Pacific strengthen the Hadley Cell, enhancing subsidence over the eastern Pacific and reducing upper-level westerlies over the Atlantic. This results in lower vertical wind shear in the MDR (and typically allows for +SSTA in May-June, more on that later though).

Something else I wanted to highlight here is that the Agulhas Current (southeastern African coast) and Mozambique Current (western Indian Ocean) are warm western boundary currents, but they exhibit negative SSTAs in May during active Atlantic hurricane seasons. I would need to look more into this, but I believe the correlation in May is that these cooler currents weaken convection in the eastern tropics, strengthening the Walker Circulation and favoring low-shear conditions in the Atlantic MDR.

While I didn’t highlight the far northern region of the Atlantic near Greenland (I am hesitant to highlight polar regions for SSTA with this product), a warmer pattern is also observed here north of the Gulf Stream. We can also see that the area off the Northeast United States (highlighted Gulf Stream) tends to be cooler (which has more to do with the next variable we’ll look at).

For the most part, there are mixed signals here in May 2025 compared to active years (the northern part of the Canary Current is warm but reduced anomalies southward, warmer western Atlantic, reduced signals near Africa, etc.). However, I don't want to underestimate how much ENSO can influence patterns in a hurry, especially during the later parts of the season. This will be a good test to see how much influence it has as we progress (and look at June and July data later this year).

Geopotential Heights
The ocean surface and atmosphere share a complex, interdependent relationship, where changes in one system often drive significant responses in the other. Analyzing 500mb geopotential height anomalies provides a robust method for identifying key atmospheric features (such as high and low-pressure systems, ridges, troughs, etc.).




++ Anomalies ++
Northwestern Pacific

-- Anomalies --
North Atlantic
Northeastern Pacific
Europe

While there are mixed signals in the SSTA product for the Atlantic region, there is a stark difference in the 500mb geopotential heights. One of the first things that jumps out is the pattern over the CONUS and North Atlantic region for active years—a weakened Bermuda/Azores High in the North Atlantic region and lower heights extending all the way to the Northwestern CONUS/Northeastern Pacific. This makes sense, weakened/northward displaced Bermuda High -> zonal winds are reduced -> this allows for +SSTA throughout the MDR/Atlantic. In May 2025, we’ve essentially had the opposite, with a ridge extension through the GOM, subtropics, and all the way into the Northern Atlantic. This has led to +SSTA in the subtropics and western Atlantic, but has muted warming in the eastern Atlantic.

Some of the other correlations though in May 2025 (like Europe and the Northwestern Pacific) are comparable to active years. In the Atlantic, lower heights over Europe typically weaken the downstream extension of the Azores/Bermuda High, reducing wind shear. In the Pacific, a robust ridge in the Northwestern Pacific enhances the Hadley Cell, promoting subsidence in the eastern Pacific and weakening upper-level westerlies over the Atlantic. Positive SSTAs in the Kuroshio Current, as discussed earlier, align with these height anomalies, reinforcing the teleconnection between Pacific warmth and Atlantic hurricane activity. Negative 500mb height anomalies in the Northeastern Pacific suggest a persistent trough featured or lowered heights, often associated with a northward-shifted jet stream or La Nina’s influence on Pacific circulation. This reduces the strength of the Pacific subtropical high, altering global teleconnections.

Overall though, we continue to have these competing mechanisms. The next two variables we will examine are indirectly connected to the previously discussed factors, as they are strongly influenced by geopotential height anomalies and SSTA.

Zonal Winds
The first variable, 850mb zonal winds, represents low-level atmospheric flow near the surface (~1500 km in height). These winds are critical for understanding the configuration and evolution of sea surface temperature anomalies and contribute a pivotal role in modulating ocean-atmosphere interactions.




++ Anomalies ++
Polar Front Region Extension
ITCZ Africa Extension

-- Anomalies --
ENSO Region
Subtropical Region Extension

For the Pacific, we again largely focus on the ENSO region. Weaker low-level easterlies in the Pacific indicate an established/developing La Nina (warmer SSTs -> lower shear -> enhanced convection). I’ve also highlighted the ITCZ Africa Extension, where stronger easterly winds at 850mb reflect an active West African Monsoon and is largely driven by seasonal heating over the African continent. Stronger-than-normal easterly winds at 850mb reflect an enhanced low-level flow, which strengthens moisture convergence and convection in the ITCZ.

This is something definitely worth digging more into, but my guess is an early monsoon signal is in lock step with the MJO phase, which with persistence would lead to a robust setup for generating AEWs later in the summer. Compared to active years, the Pacific and ITCZ signals in May 2025 correlate to active years. Once again though, the North Atlantic configuration doesn’t support this.

I’ve highlighted these as Polar Front Region and Subtropics Region, but really what we are looking at is this dipole of zonal winds. In active years for May, negative 850mb zonal wind anomalies in the polar front region indicate a weaker Bermuda/Azores High (and a northward shift of the polar front jet stream). This weakens the low-level easterly trade winds typically driven by the subtropical high, resulting in a relative increase in westerly flow or reduced easterly flow at 850mb. These anomalies signal a large-scale atmospheric pattern that persists into the hurricane season, reducing vertical wind shear in the tropical Atlantic. Conversely, stronger easterly winds at 850mb in the subtropics, combined with weaker upper-level westerlies (again, often linked to La Nina), reduce vertical wind shear in the MDR.

The May signal for active years indicates that this low-shear pattern is likely to persist into the summer. Additionally, stronger easterly winds in the subtropics can limit upwelling in the tropical Atlantic, allowing warmer SSTs to persist in the MDR. For May 2025 though, the dipole anomalies are completely flipped. It will be interesting to see if this continues, as it would be a competing mechanism with ENSO with regards to shear/instability in the MDR and Caribbean.

Precipitation
The last variable I want to look at is precipitation. I want to stress that, while these anomalies are not direct predictors of Atlantic hurricane season activity, they are strongly correlated with the atmospheric and oceanic factors discussed previously. Precipitation anomalies in May largely serve as a diagnostic tool, reflecting the state of large-scale circulation patterns, monsoon dynamics, and ocean-atmosphere interactions that establish the conditions for active hurricane seasons.





++ Anomalies ++
Caribbean + Western MDR
Central + Eastern Africa
Western Pacific
Indian Monsoon

-- Anomalies --
Eastern Pacific

Positive precipitation anomalies in the Caribbean and western MDR indicate enhanced convective activity, driven by warm SSTs and low-level moisture convergence in May. This is often linked to an established La Nina or cold neutral ENSO phases, which reduce upper-level westerlies and wind shear, fostering convection. Positive precipitation anomalies in Central and Eastern Africa reflect an early and robust onset of the West African Monsoon (WAM) and a northward-shifted ITCZ. These are driven by stronger low-level easterly winds (positive 850mb zonal wind anomalies) and warm SSTs in the Canary Current, which enhance moisture convergence and convection.

Positive precipitation anomalies in the Western Pacific are driven by warm SSTs in the Kuroshio Current and a strengthened Pacific subtropical high (and again, more linked to the oceanic-atmospheric ENSO configuration). In theory, enhanced convection in the Western Pacific strengthens the Walker Circulation, reducing upper-level westerlies and wind shear in the Atlantic MDR. Conversely, negative anomalies exist in the eastern Pacific. Interestingly, there is a strong correlation between an active Indian monsoon season in May and an active Atlantic hurricane season (perhaps MJO phase position related?).

Looking at May 2025, we again have a much drier Caribbean + Western MDR, mixed signals in the eastern Pacific and western Pacific, but a strong signal with the Indian monsoon. Neutral conditions appeared over Africa.

Image Links for All Seasons
If you want to look at the anomalies for each individual active year, I put them here.
SSTA - https://imgur.com/a/Qh715i2
500mb height - https://imgur.com/a/WZEeWIj
850mb zonal wind - https://imgur.com/a/Yg3sLUt
Prate - https://imgur.com/a/bpagLYB

I’ll do this again for June data sometime next week. Definitely let me know if you have any ideas for future implementations. Some ideas that I've come up with so far:

• Adding additional datasets (perhaps something that goes back to 1850)
• I wanted to lean more towards visuals, but we could do correlation metrics (or build a statistical model)
• Incorporate functionality for other basins
• Adding more variables (like velocity potential, meridional winds, etc.)
• Building some sort of user interface to allow the ability to do this for custom time ranges (currently this is a Python program I created that allows a date range and year array)

[GCANE]

Going to be watching SE end of the GOM over the weekend. Around 23N 85W.
Nothing on the models but area is forecast to have high CAPE, low surface winds, and will be between two ULLs.
Chances are low but nothing else out there to watch over the weekend.

[GCANE]

Going to be watching SE end of the GOM over the weekend. Around 23N 85W.
Nothing on the models but area is forecast to have high CAPE, low surface winds, and will be between two ULLs.
Chances are low but nothing else out there to watch over the weekend.

Area currently does have a decent 500mb vort and low shear. Strong convection may drop that vort down to the surface. Wait and see.

[cycloneye]

 https://x.com/AndyHazelton/status/1943666382060568993

[DorkyMcDorkface]

 https://x.com/AndyHazelton/status/1943666382060568993

EPS seems more bullish on that signal as posted above. I guess we'll see which one comes closer to verifying

[OURAGAN]

Strong 700 MB vorticy with the wave along 26 W

[OURAGAN]

700 MB vorcity

[WeatherBoy2000]

The mdr has rapidly warmed up in the last few weeks. Now ranging from 0.3-0.5c above normal, the warmest it's been in a while:

[chaser1]

15 day SST change also implies slight warming in the far Eastern Pacific as well. Possible connection for a end of month "waning" MJO signal back inside the circle? With unknowns such as whether Uncle SAL has moved out of the East/Central Atlantic by early August, increased EPAC SST's might just continue to aid toward continued broad (Atlantic) basin stability. 'Course, that wouldn't necessarily eliminate additional home-grown or subtopics genesis. Hopefully though, that pattern persistence will continue to cap storm intensities for a good portion of next month.

[WeatherBoy2000]

15 day SST change also implies slight warming in the far Eastern Pacific as well. Possible connection for a end of month "waning" MJO signal back inside the circle? With unknowns such as whether Uncle SAL has moved out of the East/Central Atlantic by early August, increased EPAC SST's might just continue to aid toward continued broad (Atlantic) basin stability. 'Course, that wouldn't necessarily eliminate additional home-grown or subtopics genesis. Hopefully though, that pattern persistence will continue to cap storm intensities for a good portion of next month.

Yeah it's still not super favorable, but it's definitely more favorable than it was back in June. Gotta see if the warming trend continues and if it is paired with the predicted cooling enso as well.