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

[Iceresistance]

End of March observation of the SST Anomalies . . .



Much of the EPAC is below normal & most of the Altantic is above normal (The Gulf of Mexico is REALLY warm this time of the year)

[DorkyMcDorkface]

May you kindly make a similar animated sequence for the forecast STSD during ASO, going back to 2017?

Sure:

https://i.ibb.co/C1nh47g/ezgif-2-3e9d224c5cac.gif

By “STSD” I was referring to the Standardised Tropical-Storm Density. May you please post the animated sequence for those?

Interestingly, the SST profile, with + anomalies over the Gulf of Guinea, suggests -AMO, yet the NS/H suggest otherwise.

My bad, here you go:

[Shell Mound]

Sure:

https://i.ibb.co/C1nh47g/ezgif-2-3e9d224c5cac.gif

By “STSD” I was referring to the Standardised Tropical-Storm Density. May you please post the animated sequence for those?

Interestingly, the SST profile, with + anomalies over the Gulf of Guinea, suggests -AMO, yet the NS/H suggest otherwise.

My bad, here you go:
https://cdn.discordapp.com/attachments/733552978572869632/828679091019710524/ezgif-6-9790f2252bcf.gif

The latest forecast suggests steering currents rather similar to those in ASO 2019: storms turning sharply northward, with harrowingly close calls (i.e., Dorian).

[NXStumpy_Robothing]

By “STSD” I was referring to the Standardised Tropical-Storm Density. May you please post the animated sequence for those?

Interestingly, the SST profile, with + anomalies over the Gulf of Guinea, suggests -AMO, yet the NS/H suggest otherwise.

My bad, here you go:
https://cdn.discordapp.com/attachments/733552978572869632/828679091019710524/ezgif-6-9790f2252bcf.gif

The latest forecast suggests steering currents rather similar to those in ASO 2019: storms turning sharply northward, with harrowingly close calls (i.e., Dorian).

Considering Dorian made landfall in North Carolina as a mildly powerful hurricane and completely devastated the Bahamas (as well as doing significant amounts of additional damage as a post-tropical cyclone in Canada), I don't think Dorian is the best usage of a close call. I'm aware you're most likely referring to southeast Florida, but steering currents like 2019 would make for a very bad season for those living on islands off the US East Coast. Regardless, a discussion about Dorian is not necessarily a discussion to be had here, and I'll stop before rambling further on that topic.

Moving on to steering currents, the natural climatology of Atlantic hurricanes support recurves, so seeing that being supported by certain model runs is not necessarily surprising. It's more anomalous to get west-based seasons like last year (which still had its fair share of recurves), where there's a blocking pattern established to steer the storms into the North American mainland. Besides, even if the pattern generally favors systems avoiding land and gunning northeast out to sea, all it takes is for one untimely shift in that pattern, and instead you're dealing with a storm getting steered towards land and causing massive damage (2012's Sandy comes to mind here). I'd welcome a recurve-heavy season (and I personally expect something similar to 2011/2012 in terms of storm tracks) but I wouldn't bet on that being a failproof shield.

[Category5Kaiju]

Just curious but what was the prediction for the storm tracks in years like 2005, 2010, or 2017 this early in the season? I know 2005 was a heavy landfall year while 2017 was a mild recurve year and 2010 a heavy recurve year, so just wondering how those early predictions would compare with 2021

[Shell Mound]

My bad, here you go:
https://cdn.discordapp.com/attachments/733552978572869632/828679091019710524/ezgif-6-9790f2252bcf.gif

The latest forecast suggests steering currents rather similar to those in ASO 2019: storms turning sharply northward, with harrowingly close calls (i.e., Dorian).

Considering Dorian made landfall in North Carolina as a mildly powerful hurricane and completely devastated the Bahamas (as well as doing significant amounts of additional damage as a post-tropical cyclone in Canada), I don't think Dorian is the best usage of a close call. I'm aware you're most likely referring to southeast Florida, but steering currents like 2019 would make for a very bad season for those living on islands off the US East Coast.

Yes, I was referring mainly to Southeast Florida. I should add that, while I expect most storms to curve OTS this year, there may be one exception that could impact the Bahamas before curving just offshore of the U.S. East Coast. I think the Bahamas, Bermuda, and the Outer Banks are at highest risk this year, based on the indicators that have been discussed and pointed out thus far. The Caribbean will likely revert to being a dead zone once again, and I expect much less activity in the Gulf than we observed last year. Tracks in 2021 should tend to consolidate just north of the MDR and/or over the subtropical Atlantic, make some feints westward, and then curve mainly OTS, with one exception possibly following a path, if not intensity, similar to Dorian’s (hopefully, an event of that magnitude won’t transpire for decades to come). I don’t want to wander too far OT, however, but I just needed to clarify this. The ECMWF, NMME, and CanSIPS certainly do hint at more poleward tracks in 2021 compared to recent seasons.

[Shell Mound]

Just curious but what was the prediction for the storm tracks in years like 2005, 2010, or 2017 this early in the season? I know 2005 was a heavy landfall year while 2017 was a mild recurve year and 2010 a heavy recurve year, so just wondering how those early predictions would compare with 2021

More than half—ten—of 2017’s seventeen NS either made landfall or passed close to land masses, so 2017 was clearly west-biased as well.

[Category5Kaiju]

Yeah I think it very important either way to consider that just because a predominantly OTS season is expected that does not necessarily mean significant land impacts are not going to occur. Some good examples of this are 1926, 2003, and of course 2019. In fact, late season activity like in October usually favors activity in the Gulf and WCAR, and as the CANSIPS actually is predicting a wetter Gulf in October, that could be favorable for any TCs that spawn due to the CA gyre. In other words, it wouldn't surprise me in the very least if we get a season where most storms head OTS but a select few become powerful and threaten areas like the Bahamas, Florida Strait, or even W Florida late season.

[DorkyMcDorkface]

Sorry to bring up yesterday's ECMWF SEAS5 run again but this also sort of caught me by surprise: due to a not-so-great climo period (1993-2016 is overwhelmingly +AMO) this model has a very evident +MSLP bias in the Atlantic; however, it appears that for this run pressures in the central and eastern Atlantic are depicted as average to slightly above average by ASO.


Compare to previous years (yes, including 2017 and 2020) and you'll see why this interests me:

Something else of note with this year's run is the widespread positive MSLP in the Pacific; looks like it's keeping the walker circulation in Niña mode despite warming ENSO? That would certainly help the Atlantic's case in that regard.

[NDG]

I would expect a nice warm up of SSTs across the Tropical Atlantic Basin over the next few days with the NAO going well negative since early February.

[SFLcane]

That ACE prediction (which is quite active by ECMWF standards for the Atlantic) is really weird given its (fairly typical) depiction of a dry MDR.

[cycloneye]

That ACE prediction (which is quite active by ECMWF standards for the Atlantic) is really weird given its (fairly typical) depiction of a dry MDR.

Something is not right about those two different scenarios despicted by the model.

[SFLcane]

Scratching head...

 https://twitter.com/bennollweather/status/1379550812251168769

[Iceresistance]

Scratching head...

https://twitter.com/bennollweather/status/1379550812251168769

Maybe 2020 created this weirdness

[Kingarabian]

That ACE prediction (which is quite active by ECMWF standards for the Atlantic) is really weird given its (fairly typical) depiction of a dry MDR.

It's not just the Euro, I believe the Canadian seasonal is doing the same thing.

[BYG Jacob]

The Euro is predicting a very active season in spite of its well-known dry bias, yikes.

[Shell Mound]

Yeah I think it very important either way to consider that just because a predominantly OTS season is expected that does not necessarily mean significant land impacts are not going to occur. Some good examples of this are 1926, 2003, and of course 2019.

Seven of 1926’s eleven NS and ten of 2003’s sixteen NS made landfalls, so those years are not particularly good examples.

Anyway, the EC suggests an active season despite a borderline Niño and general -AMO signature (+ Gulf of Guinea). Why?

[Shell Mound]

So far, the EC, CanSIPS, and CFSv2 all agree that the Caribbean will likely be drier than normal during ASO, while the eastern portion of the MDR could be more active than usual, as in years such as 2009. There is also general agreement that tracks will tend to move poleward, over the open Atlantic, during the same timeframe. The EC, unlike the CanSIPS and CFSv2, hints at more Gulf activity than usual during ASO, whereas the other two models suggest a drier-than-average GoM. But the general consensus seems to be that storms are more likely to form farther east and track farther north, that is, OTS, during the peak of the 2021 Atlantic hurricane season. The drier-than-average Caribbean also suggests that late-season activity is likely to be less intense than expected, which would reduce the threat of an October threat to places such as, say, Florida. If anything homegrown does manage to form, the EC suggests that it could develop over the GoM and track generally northeastward, like Nestor or Olga in 2019. Maybe 2009 and 2019 might be analogous in terms of genesis and some general tracks. Warm neutral or + ENSO tends to result in more OTS tracks due to a stronger TUTT and weaker mid-level ridging.

[tolakram]

Out of curiosity, has any pre-season prediction of general tracks been anywhere close to accurate? Every spring we seem to go through some of these discussions with no regard for how any of these have verified in the past. Not that there's anything wrong with analyzing what the models are saying.

[Category5Kaiju]

Out of curiosity, has any pre-season prediction of general tracks been anywhere close to accurate? Every spring we seem to go through some of these discussions with no regard for how any of these have verified in the past. Not that there's anything wrong with analyzing what the models are saying.

I may not be the best person to ask given I am no professional met but rather a 19-year old wx geek who started closely tracking hurricanes in 2018, but what I have heard 2017 started off with a pretty OTS signal but ended up being a devastating landfall year. Of course, 2017 was also expected to be an El Nino year, which do tend to favor OTS tracks. However, then you have La Nina years like 2010 or 2011 where many storms are OTS