Talking the Tropics With Mike: Dorian slowly strengthening with possible Florida hit late Sunday

Aug. 29, 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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DORIAN:

It's still early on this one but POSSIBLE Jacksonville/NE Fl./SE Ga. impacts (primarily later Sun./Mon.) & very dependent on exact location & intensity of Dorian:

* increasing & potentially deadly rip current risk at area beaches (as early as Fri. due to steady onshore flow).  Always swim & surf with a "buddy" & as near a lifeguard as possible though best advice is to stay out of the water! Rip current explainer & safety info * here *.

* rough seas & surf... some coastal flooding (accentuated by new moon phase Fri. in addition to heavy rain) + above avg. tides at the coast, St. Johns River & its tributaries.

* breezy winds out of the east/southeast 15-20 mph, higher gusts.... peak wind gusts could reach 50+ mph Sunday into early next week depending on positioning & strength of Dorian.

* several periods of heavy showers & t'storms, but it's not looking like a "washout" for the weekend.... wettest Sunday into Monday.

* isolated fast-moving tornadoes/waterspouts

Dorian became a hurricane upon approach to Puerto Rico Wed. afternoon with the eye moving a little east & northeast of the island nation sparing Puerto Rico the worst of its wrath but not so for the U.S./ British Virgin Islands. Dorian is still battling against the dry air that's been keeping the storm's intensity in check while moving into a lower shear environment, but the central pressure continues to slowly drop indicating intensification.  Dorian will now be over the open Southwest Atlantic for at least several days. It is worth noting that Dorian is a small/compact system - tropical storm force winds extend about 80 miles from the center - & therefore may be susceptible to even small changes in its environment (shear/ dry air/land) resulting in wide intensity swings over a short period of time.  In any case.... anyone with travel plans to the Caribbean through the week & the Bahamas through the weekend should stay up to date on the latest forecasts.  All warnings for Puerto Rico, the Dominican Republic & Virgin Islands have been dropped as conditions quickly improve.

As for beyond the Caribbean..... it looks like Dorian's core has become well established.  The positioning of a rather narrow but significant upper level ridge of high pressure across the Central Atlantic will be a key factor in the future movement. The upper level high will act as a brick wall stopping the northward movement that virtually all of the models have missed so far. The European model has become consistent  with Dorian generally strengthening over the SW Atlantic before reaching the Florida coast over the weekend.  The GFS model has joined many of the other forecast models in showing a more northwest & even northward movement across the SW Atlantic & Bahamas then near or into Florida (depends on the model run) over the weekend or early next week but generally as relatively week tropical cyclone. The UKMET model has been showing a similar trend as the European though generally stronger (but has not done particularly well w/ "Erin" - too strong, too far west).  However, the UKMET has been lacking consistency.  It's not wise to jump on a single model run or even a single model.  And there will continue to be changes & updates.  The GFS is now the northern outlier & slowest while the European is the fastest/strongest & the more southern outlier. The conditions over the SW Atlantic & near the Bahamas do appear quite favorable for at least maintaining Dorian if not allowing for strengthening.  We need to be aware of the potential for a stronger tropical cyclone in the long term than is currently indicated by models &/or forecasts.

It seems likely that an exiting trough over the Northwest Atlantic this week (helping to steer Erin N/NE) will not be strong enough to pick up Dorian.  Instead, high pressure will rebuild in place of & south of the exiting trough turning Dorian back more to the west/northwest & possibly west upon approach to Florida & the S.E. U.S. coast.

So.... the bottom line is stay up to date on the latest forecasts for the Caribbean, Fl. & Southeast U.S. this week into the upcoming holiday weekend.  There will be changes in the forecast & impacts in the days ahead! Don't be so foolish as to look at a forecast one day & not return for an update whether it's 1, 3 or 5+ days later.

Spaghetti model plots for Dorian:

Ensemble (An ensemble weather forecast is a set of forecasts that present the range of future weather possibilities) spaghetti plots: (for an in-depth look on ensemble modeling see * this * [Blake/Brennan, NHC])

And remember what that "cone of concern or uncertainty" means & does not mean.  That cone has everything with the historic track error ranging from the moment the forecast was issued all the way out to 5 days when the avg. error is nearly 200 miles!

National Hurricane Center average track error starting with 12 hours & ending at the 120 hour forecast from 2014-'18:

IR satellite:

Tropical wave '98-L' was upgraded to tropical depression #6 late Mon. then to tropical storm "Erin" Tue. night before weakening again to a depression  over the Western Atlantic between Bermuda the U.S.  Rip currents along area beaches are the biggest threat from the Mid Atlantic to New England.

No change in the movement forecast.  After a slight slow north/northwest movement, an upper level trough to the north will become the main steering mechanism accelerating & taking the storm well east of the U.S. east coast  & west & northwest of Bermuda.  Other than the rip current risk along the U.S. east coast, no major direct impacts are expected & certainly no impacts for NE Fl./SE Ga.

An examination of dust over the Central & Eastern Atlantic shows a continuation of a good deal of dust over the Central & Eastern Atlantic as well as parts of the Caribbean.  Dorian has been trying to fight off this dry air the last several days.

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

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. along with parts of the Central Caribbean.....

SE U.S. surface map:

Surface analysis centered on the tropical Atlantic:

Surface analysis of the Gulf:

Caribbean:

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