2021 Indicators: SST's / SAL / MSLP / Shear / Steering / Instability / Sat Images

[aspen]

http://twitter.com/tylerjstanfield/status/1413979914680901635?s=21

Very interestingly, all but 2001 had multiple long-tracking Cape Verde/MDR hurricanes like the Berthas, Ike, Floyd, Gert, and more. 2001’s two long trackers, Erin and Felix, opened up in the MDR before regenerating and peaking further north. It would seem that the Atlantic Nino helps make the MDR more productive if SSTs aren’t that impressive, but this is a pretty small sample size.

I also want to bring up 2018 again due to its MDR SSTs that looked pretty awful early on. I’ve already mentioned Florence alongside many others, but there’s a second system worth noting: Helene, which was designated as a TD the moment it moved off of Africa and nearly hit major intensity rather far east. Would anyone have anticipated that just by looking at the pre and early season SST profile and nothing else?

[Category5Kaiju]

I would also like to point out a crucial, magic number: 26. That is, 26 degrees C, which is the minimal temperature required for TSs to generally form. You could theoretically have a 27 or 26 degree C MDR by peak season, but assuming you have otherwise very favorable conditions (low shear, little dust, high upper ocean heat content, etc.), tropical storms can still get going there.

[Yellow Evan]

I would also like to point out a crucial, magic number: 26. That is, 26 degrees C, which is the minimal temperature required for TSs to generally form. You could theoretically have a 27 or 26 degree C MDR by peak season, but assuming you have otherwise very favorable conditions (low shear, little dust, high upper ocean heat content, etc.), tropical storms can still get going there.

A hostile SST profile would make this relatively difficult because the ocean and atmosphere are coupled.

[Category5Kaiju]

I would also like to point out a crucial, magic number: 26. That is, 26 degrees C, which is the minimal temperature required for TSs to generally form. You could theoretically have a 27 or 26 degree C MDR by peak season, but assuming you have otherwise very favorable conditions (low shear, little dust, high upper ocean heat content, etc.), tropical storms can still get going there.

A hostile SST profile would make this relatively difficult because the ocean and atmosphere are coupled.

Well yes, I obviously know that in reality such an occurrence is highly unlikely (that's why at least for my thought process I indicated "theoretical"). I guess a better point I should make is you can have seasons like 2005 or 2020 have very anomalous MDR sst anomalies but have little to no potent storms in the MDR and still end up with a hyperactive season, or you can have a season like 1999 or 2018 have above average activity in the MDR despite initially having so-so sst anomalies in the MDR

[captainbarbossa19]

I would also like to point out a crucial, magic number: 26. That is, 26 degrees C, which is the minimal temperature required for TSs to generally form. You could theoretically have a 27 or 26 degree C MDR by peak season, but assuming you have otherwise very favorable conditions (low shear, little dust, high upper ocean heat content, etc.), tropical storms can still get going there.

A hostile SST profile would make this relatively difficult because the ocean and atmosphere are coupled.

Well yes, I obviously know that in reality such an occurrence is highly unlikely (that's why at least for my thought process I indicated "theoretical"). I guess a better point I should make is you can have seasons like 2005 or 2020 have very anomalous MDR sst anomalies but have little to no potent storms in the MDR and still end up with a hyperactive season, or you can have a season like 1999 or 2018 have above average activity in the MDR despite initially having so-so sst anomalies in the MDR

One thing that could be really dangerous is if SSTs become very favorable in the Caribbean and Gulf while the MDR is somewhat hostile. This would not be the first time something like this happened.

[Category5Kaiju]

A hostile SST profile would make this relatively difficult because the ocean and atmosphere are coupled.

Well yes, I obviously know that in reality such an occurrence is highly unlikely (that's why at least for my thought process I indicated "theoretical"). I guess a better point I should make is you can have seasons like 2005 or 2020 have very anomalous MDR sst anomalies but have little to no potent storms in the MDR and still end up with a hyperactive season, or you can have a season like 1999 or 2018 have above average activity in the MDR despite initially having so-so sst anomalies in the MDR

One thing that could be really dangerous is if SSTs become very favorable in the Caribbean and Gulf while the MDR is somewhat hostile. This would not be the first time something like this happened.

I second that; also, what is also (I would think) true is that at least for what the predictions are for activity this year, if low latitude waves are the norm, then that would conceivably mean they would have an easier time tapping into the high UOHC off the northern coast of South America and have an easier time to ventilate and avoid any surge of SAL to the north. Also with the perilous ridging that *could* manifest and the very wet Sahel, I would have to think that it would also be conceivable that the MDR is practically shifted southward, which would also heighten the risk of having intense, extremely low latitude CV systems impacting the Atlantic coasts. While I am in no way trying to say that we will see a repeat per se, Caribbean cruisers may make a comeback, and this is something we certainly need to keep an eye out for.

[SootyTern]

Wouldn't Western Atlantic or Eastern continental ridging steer low latitude storms below South Florida/US East Coast and instead threaten similar areas that were impacted in 2020?

[Category5Kaiju]

Wouldn't Western Atlantic or Eastern continental ridging steer low latitude storms below South Florida/US East Coast and instead threaten similar areas that were impacted in 2020?

It really depends on the timing. Last year I believe the ridge was extremely wide and strong with little troughiness that disrupted it, which allowed storms like Eta or Iota to slam right into Central America at their peaks. However, while that may be possible with the ridging predicted to take place this year, I think this ridging pattern seems to be quite eerily similar to the one seen in 2004, where it was directly positioned over eastern Canada, which meant storms that would otherwise recurve would instead get blocked by it and move more westward, which would especially put Florida under the gun. However, the ridging that is predicted to be in place does not seem to be extremely strong and wide, meaning trapped storms that are low latitude could "feel" any troughiness that sets in, only for their curve northward to take place once they are in the Caribbean Sea or more concerningly in the Western Caribbean Sea, where a northward recurve would likely put Gulf coast regions at risk.

[Shell Mound]

Now that the suppressive phase has arrived and the MDR is cooling off a bit due to the SAL surges, there's a bit of "MDR sst hand-wringing" going on again that I see, especially on social media. However, also what I have noticed is that comparisons with 2004 are being brought up with the ridging forecast to endanger Florida later this season. So, allow me to share the sst anomalies map of 2004 on the same day we are in of the calendar year.

https://www.ospo.noaa.gov/data/sst/anomaly/2004/anomnight.7.10.2004.gif

MDR did not look that impressive back then, didn't it?

Actually, there is a strong +AMO “horseshoe” (warm U-tongue from N ATL → MDR) + cool Gulf of Guinea, so the SST configuration on that map is quite conducive.

[Shell Mound]

Even according to the Coral Reef map, much of the Atlantic is seeing cool SST anomalies, and the MDR is roughly 0.2C below normal for this time of year.

The MDR is actually warmer than average:

[Shell Mound]

Check out the years Boston is going up against for record rainfall for July. ALL years had at least one major hurricane strike on the US coast.

https://twitter.com/NWSBoston/status/1413980133271113732?s=19

That is a very sinister observation indeed. 1915 it was New Orleans, 1921 it was Tampa Bay, 1938 it was New England with Yankee Express, and 1959 it was Gracie in North Carolina...

Gracie actually struck South Carolina as a strengthening Cat-4. (Incidentally, Danny struck SC as well.) Also, 1915 featured the second major hurricane in Galveston.

[Shell Mound]

 https://twitter.com/webberweather/status/1414048928509554690



 https://twitter.com/webberweather/status/1414049678597885955



 https://twitter.com/webberweather/status/1414052044504113152



 https://twitter.com/PlinianWinds/status/1413871510075416579



 https://twitter.com/cyclonicwx/status/1413876166612619272

[NotSparta]

With Africa being so wet and the 700mb pattern having even stronger low-latitude westerlies/anomalous cyclonic flow I am curious to see if you get monsoonal messes that helped to tamp down 2020's MDR or if that was a fluke. So far, 2021 is another, possibly even stronger, year with this pattern. Something happened in 2018 and it hasn't gone away since

[Shell Mound]

http://twitter.com/tylerjstanfield/status/1413979914680901635?s=21

Very interestingly, all but 2001 had multiple long-tracking Cape Verde/MDR hurricanes like the Berthas, Ike, Floyd, Gert, and more. 2001’s two long trackers, Erin and Felix, opened up in the MDR before regenerating and peaking further north. It would seem that the Atlantic Nino helps make the MDR more productive if SSTs aren’t that impressive, but this is a pretty small sample size.

I also want to bring up 2018 again due to its MDR SSTs that looked pretty awful early on. I’ve already mentioned Florence alongside many others, but there’s a second system worth noting: Helene, which was designated as a TD the moment it moved off of Africa and nearly hit major intensity rather far east. Would anyone have anticipated that just by looking at the pre and early season SST profile and nothing else?

Even with the Atlantic Niño in place, comparison makes clear that June 2021 had a much more -AMM/-AMO than the average of those other years.

[SFLcane]

 https://twitter.com/wxtca/status/1413952295327342594

[Shell Mound]

With Africa being so wet and the 700mb pattern having even stronger low-latitude westerlies/anomalous cyclonic flow I am curious to see if you get monsoonal messes that helped to tamp down 2020's MDR or if that was a fluke. So far, 2021 is another, possibly even stronger, year with this pattern. Something happened in 2018 and it hasn't gone away since

With a coolish MDR, very warm subtropics, and suppressive MJO at times, this could certainly combine with the ASW to yield more homegrown vs. MDR cyclones.

[aspen]

What is the CFS saying for potential TC formation and activity? I remember last year it was pretty decent at sniffing out some TCs, including Isaias, as much as a month before they formed.

[USTropics]

Here are some high-def images from the July NMME forecast for precipitation rates (lead time months and seasonal):

August


September


October


ASO

[aspen]

Here are some high-def images from the July NMME forecast for precipitation rates (lead time months and seasonal):

August
https://i.imgur.com/9EKwZT4.png

September
https://i.imgur.com/oKqRQQV.png

October
https://i.imgur.com/J3GHmIu.png

ASO
https://i.imgur.com/bIWd4WC.png

If those precipitation forecasts verify, then August could be a lot less favorable than I thought — lower precipitation all across most of the MDR, east coast, Caribbean, and Gulf. September and October, on the other hand, are looking better, and those maps might suggest potential in the western Caribbean.

All three have lower-latitude strips of high precipitation and might suggest lower-latitude waves and storms. If MDR SSTs still aren’t that impressive by early August, low-rider waves will be able to stick in the warmest waters before reaching the Caribbean, so we might have to watch out for more tracks like Elsa and Ivan.

[Category5Kaiju]

With Africa being so wet and the 700mb pattern having even stronger low-latitude westerlies/anomalous cyclonic flow I am curious to see if you get monsoonal messes that helped to tamp down 2020's MDR or if that was a fluke. So far, 2021 is another, possibly even stronger, year with this pattern. Something happened in 2018 and it hasn't gone away since

But we did get 3 Cape Verde systems in 2018 didn't we? Idk, I guess I am being too simplistic here, but the fact that we already had very impressive 94L, 95L, and eventually Elsa that went on to become a hurricane in the MDR (as well as the Atlantic Nino allowing for waves to be spit off at lower than normal latitudes where they can go on and form possibly into TCs) makes me want to believe that unlike last year the "clumping of waves" may not be as huge of a problem. We'll see.