Talking the Tropics With Mike: T.D. #9 strengthens into tropical storm Humberto near the Bahamas

Sept. 14, 2019 — The "Buresh Bottom Line": Always be prepared!.....First Alert Hurricane Survival Guide... City of Jacksonville Preparedness Guide... Georgia Hurricane Guide.  

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RECAP "Hurricane Dorian: A True Tropical Beast"

Potential local - Jacksonville/NE Fl./SE Ga. - impacts from Humberto - magnitude to be determined by exact location & intensity of the system relative to Jacksonville!:

* scattered showers & isolated t'storms over the weekend - diminishing Monday

* rough seas & surf with a high rip current risk.  Best advice is to stay out of the ocean this weekend.

* minor flooding along the coast as well as the St. Johns River & its tributaries, especially at times of high tide with some astronomical boost from the full moon phase.

* breezy winds out of the east Sat. then east/northeast Sunday that will veer to out of the north then northwest Monday - offshore winds for surfers!

* virtually no impacts inland

Tropical depression #9 was upgraded late Friday afternoon then to tropical storm Humberto late Fri. evening - over & near the SE Bahamas  - continues to move ever so slowly while trying to organize in the face of strong shear.  As thunderstorms fire, the center will likely have a tendency to "jump around" from time to time requiring new "fixes" on its initial position.  Hurricane hunter aircraft have been finding a tilted circulation from the surface to aloft indicating the shear is still taking a toll.  Though not in a particularly favorable area for much development at the moment - a good deal of shear out of the west & southwest that was 30-40 mph & now is about 20-30 mph - the wave will find a more favorable environment  over the far Northwest Bahamas & east of Fl. over the weekend.  For the hard hit Northern Bahamas, this wave will bring some heavy rain & - at times - gusty winds but at this time a real strong tropical system is not expected to develop while in the vicinity of the Bahamas. But the heavy rain & gusty winds will interfere with search & rescue/recovery operations.

Overall conditions look favorable for organization over the weekend.  Shear will slowly decrease, & it looks as though there will be no land interaction of consequence.  The poorly organized "center" will "jump around" until the center can couch itself under the strongest convection.

We'll need to watch for a "sweet spot" that could result in fairly fast organization &, therefore, strengthening later in the weekend into early next week.  Everyone from Florida & even north to the Carolina's should stay up to date on the latest forecasts even though there's an obvious trend to the east.  The European forecast model is shifting east & several of the models are following suit.  The European model continues (since early Thu.) to keep the system well east of Florida & Jacksonville in the latest operational (every 6 hours) output with indications of perhaps a strong right hand turn at about Jacksonville's latitude. Such a track would imply few real significant impacts for Jacksonville/NE Fl./SE Ga.  The GFS is still farther west & weaker taking a weak tropical cyclone along the Florida coast but shifting east with each model run... the UKMET is close to the European solution (but has struggled some this season so far) with a hurricane but well east of the U.S. coast. Some of this discrepancy is likely because the GFS keeps the system weaker/more shallow & therefore is steered by the low level trade winds vs. a stronger/deeper system that would be steered by the mid & upper level flow (or lack thereof).

There is also low pressure trying to develop over the Central/Western Gulf of Mexico in association with an upper level low that's helping to nudge Humberto northward. The positioning & strength of the Bermuda high over the Atlantic plus an incoming upper level trough over the Northeast U.S. will again (like Dorian) play an important role in the eventual track.

By Sunday afternoon - at about 30-35,000 feet - the European model forecasts a weakening trough will be over New England while the Bermuda high starts to strengthen over the Central Atlantic & the upper low over the Gulf "peels" away to the west.  This essentially leaves an alleyway over Fl. with the question being exactly where.  One word of caution: we should be cautious of a track simply being "up & out".  We have to watch for a sneaky ridge that may try to build - especially mid Sept. &/or the upper level trough to the north ending up being farther north & moving out faster.  In any case.... the current trends are for enough of an alleyway to keep the tropical cyclone well east of Florida & the entire U.S. coast.

The Gulf Stream would possibly add some "energy" for strengthening (though some upwelling remains from Dorian).

Ensemble model forecasts for Humberto show a nice shift east:

A wide view of the Gulf/SW Atlantic shows Humberto as well as an upper low over the Gulf of Mexico that might try to develop a surface low by early next week over the Western Gulf that will need to be monitored for tropical development.

Radar imagery courtesy S. Fl. Water Management District:

5-day rainfall forecasts from the European (more east with disturbance so less rain) & GFS (more west with disturbance so wetter) respectively:

Thanks to Dorian, sea surface temps. have dropped noticeably from the Northern Bahamas extending northward for hundreds of miles.  Upwelling like this can last for at least a week depending on weather & wind conditions.  Otherwise.... sea surface temps. remain generally above avg. over the Central Atlantic & Gulf of Mexico.

There are a couple of active tropical waves over the Central & East Atlantic with long term potential & track the big question mark.  Plenty of time to watch/monitor/track & "cipher".  Most of the more reliable global forecast models - European/GFS/UKMET - are bouncing around on development not to mention the location, but the Caribbean may be faced with another named storm - "Imelda" &/or "Jerry" by later next week.

An examination of dust over the Atlantic shows generally less dust over the basin vs. past months which is fairly typical for September & the peak of the hurricane season.

2019 names..... "Imelda" is next on the Atlantic list (names are picked at random... repeat every 6 years... historic storms are retired (Florence & Michael last year) & Dorian is almost certain to be next:

East Atlantic:

Mid & upper level wind shear (enemy of tropical cyclones) analysis (CIMMS). The red lines indicate strong shear of which there is plenty across the Atlantic at the moment:

The Atlantic Basin:

Water vapor imagery (dark blue indicates dry air):

Deep oceanic heat content:

Sea surface temp. anomalies show a warm Gulf of Mexico, Central & Northwest Atlantic while the "Main Development Region" (MDR) remain cooler than avg.  Note the upwelling (cooler water) left behind Dorian over the Bahamas & east of Florida:

While the MDR is cooler than avg., it's important to realize the water is still warm enough to support tropical systems....

SE U.S. surface map:

Surface analysis centered on the tropical Atlantic:

Surface analysis of the Gulf:

Caribbean:

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