[Tropical] Tropical Cyclone Discussion

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WTNT45 KNHC 022055
TCDAT5

Hurricane Elsa Discussion Number  10
NWS National Hurricane Center Miami FL       AL052021
500 PM AST Fri Jul 02 2021

Reports from a NOAA Hurricane Hunter aircraft indicate that Elsa
has strengthened a little more since the last advisory, with a
combination of flight-level winds, SFMR surface wind estimates, and
dropsonde data showing that the maximum winds are near 75 kt.  The
aircraft also reported that the 700-mb circulation remains somewhat
disorganized, and that the 700-mb center is not vertically aligned
with with the surface center.  The former issue is likely due to
the rapid motion, and the latter may be due to the effects of
westerly shear.

The initial motion now is 290/26.  There is again little change to
the forecast track or the forecast guidance.  The guidance is in
good agreement on a rapid west-northwestward notion to near the
south coast of the Dominican Republic and Haiti by 24-30 h, followed
by a continued west-northwestward motion at a slower forward speed
through 48 h.  After that time, Elsa should gradually turn
northwestward and eventually northward as it moves through a
weakness in the subtropical ridge created by a mid-latitude trough
over the eastern United States.  This motion should take the
cyclone across Cuba and over the eastern Gulf of Mexico or the
nearby Florida Peninsula, eventually moving into the southeastern
United States by the end of the period.  The track guidance is a
little less divergent than earlier, but there is still enough spread
in the potential tracks that this part of the forecast remains low
confidence.

The latest global model runs and the associated intensity guidance
are forecasting a less favorable environment for Elsa during the
next several days.  The SHIPS model now calls for 10-20 kt of
northwesterly shear during the next 48 h, and 15-25 kt of shear
after 60 h.  In addition, the 12Z GFS forecasts a considerably
weaker storm than its last several runs.  The intensity forecast
thus calls for little change in strength during the first 24 h,
although it is possible the hurricane could strengthen a little more
during that time.  After that, land interaction and shear are
likely to cause weakening until Elsa emerges into the Gulf of
Mexico.  However, the HWRF still calls for Elsa to intensify into a
Category 3 hurricane, and like the track forecast the intensity
forecast remains of low confidence due to the spread in the
guidance.

It should be noted that the average NHC track errors are 175 miles
and 200 miles at days 4 and 5, respectively.  Given the
larger-than-normal uncertainty and because hazards will extend well
away from the center of the storm, users are urged to not focus on
the exact forecast points.

Key Messages:

1. Hurricane conditions and dangerous storm surge are expected
within the Hurricane Warning areas in Haiti and the Dominican
Republic beginning Saturday and in Jamaica beginning Sunday.

2. Heavy rainfall will gradually subside across the Windward and
southern Leeward Islands tonight, including Barbados. Outer rain
bands will impact Puerto Rico by late tonight, and affect southern
Hispaniola and Jamaica Saturday into Sunday. Isolated to scattered
flash flooding and mudslides are possible. By early next week, heavy
rain will impact the Cayman Islands and Cuba. Significant flooding
and mudslides are possible.

3. Hurricane conditions and dangerous storm surge are possible in
portions of eastern Cuba beginning early Sunday where a Hurricane
Watch is in effect. There is an increasing risk of wind, storm
surge, and rainfall impacts elsewhere in Cuba Sunday and Monday.

4. There is an increasing risk of storm surge, wind, and rainfall
impacts beginning Monday in the Florida Keys and spreading northward
along the Florida Peninsula through Tuesday. However, the forecast
uncertainty remains larger than usual due to Elsa's potential
interaction with the islands of Hispaniola and Cuba this weekend.
Interests throughout Florida should monitor Elsa's progress and
updates to the forecast.

FORECAST POSITIONS AND MAX WINDS

INIT  02/2100Z 14.2N  63.7W   75 KT  85 MPH
 12H  03/0600Z 15.4N  67.5W   75 KT  85 MPH
 24H  03/1800Z 17.0N  71.7W   75 KT  85 MPH
 36H  04/0600Z 18.3N  74.8W   70 KT  80 MPH
 48H  04/1800Z 19.9N  77.3W   70 KT  80 MPH...INLAND
 60H  05/0600Z 21.4N  79.4W   65 KT  75 MPH...OVER WATER
 72H  05/1800Z 22.9N  81.1W   55 KT  65 MPH...INLAND
 96H  06/1800Z 26.5N  83.0W   55 KT  65 MPH...OVER WATER
120H  07/1800Z 31.6N  82.0W   40 KT  45 MPH...INLAND

$$
Forecaster Beven
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