Talking the Tropics With Mike: Disorganized disturbance starting to make move NW toward Florida

Sept. 13, 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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Potential local - Jacksonville/NE Fl./SE Ga. - impacts from tropical disturbance '95-L' - 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 that will veer to out of the north then northwest Monday - offshore winds for surfers!

The tropical wave/disturbance - '95-L' - over & near the SE Bahamas - continues to crawl west/northwest while trying to organize in the face of strong shear. Hurricane hunter aircraft found a broad low pressure system with a loosely closed circulation late Thu. As thunderstorms fire, the center will likely have a tendency to "jump around" from time to time requiring new "fixes" on its initial position. A tropical storm has sustained winds of at least 39 mph. There have been occasional ship reports of wind gusts greater than 40 mph. Though not in a 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 & near 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.

Exactly what this wave will become is a bit problematic. Overall conditions look favorable for organization over the weekend. Proximity to land + a generally disorganized wave initially may hamper development. There also appears to remain a pool of cooler sea surface temps. near the Bahamas following the passage of hurricane Dorian. The poorly organized "center" may very well "jump around" the next few days trying to couch itself under the strongest convection.

But 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. Anyone along the Northeast Gulf Coast from & especially Florida & even north to the Carolina's should stay up to date on the latest forecasts. The European forecast model has been shifting north & east & several of the models are following suit. The European model continues (since early Thu.) to keep the system 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 & much weaker taking a weak tropical cyclone across Fl. but not as far west as previously - which would be wet for Jacksonville & surrounding areas... the UKMET is close to the European solution (but has struggled some this season so far). 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). The NHC has basically split the track down the middle for now with a gradual shift/correction to the east.

There is also some low pressure trying to develop over the Western Gulf of Mexico that may a play a role in the final outcome of '95-L' as it appears that some models may be having difficulty differentiating between the lower pressures over the Western Gulf & the developing Bahamian tropical disturbance. 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. There is also an upper low over the Eastern Gulf helping to enhance the shear over '95-L' as well as possibly causing a nudge northward over the next couple days.

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 system east for the most part.

The Gulf Stream would possibly adding some "energy" for strengthening (though some upwelling remains from Dorian).... while a more west outcome would mean more rain for Fl. followed by potential impacts on the Eastern Gulf Coast.

This does look a slow moving system so rainfall will be excessive IF the system comes ashore.

Ensemble model forecasts give a good idea of the uncertainty that exists with '95-L' & the wide array of possibilities:

Radar imagery courtesy S. Fl. Water Management District:

5-day rainfall forecasts from the European (more east with disturbance so less rain) & GFS (more south & 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 with 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 any development not to mention the location, but the Caribbean may be faced with another named storm - "Imelda" or "Jerry" by later next wee

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..... "Humberto" 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: