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Tropical Storm Elsa Discussion Number   4
NWS National Hurricane Center Miami FL       AL052021
1100 AM AST Thu Jul 01 2021

Just-received scatterometer data showed 35-40 kt winds to the 
northeast of the center, so the initial intensity is increased to 
40 kt.  Some slight revisions were also made to the initial and 
forecast wind radii.  Over all, the organization of the storm has 
changed little during the past several hours, with the low-level 
center partly exposed to the north and northwest of the primary 
convective band. 
 
Elsa continues to move a little faster with the initial motion now
280/24.  A rapid west-northwestward motion is likely for the next
48 h or so as Elsa is steered by the strong subtropical ridge to
the north.  After that time, the storm is expected to approach a
weakness in the ridge caused by a mid-latitude trough over the
eastern United states.  The guidance becomes rather divergent as 
this happens, as the ECWMF and ECMWF ensemble mean forecast a turn 
toward the north while the GFS and UKMET are forecasting a 
west-northwestward to northwestward motion.  The latter part of the 
new NHC forecast track will lean more toward the GFS/UKMET solutions 
at this time, but the large spread in both the deterministic models 
and the ensembles make this part of the forecast of low confidence. 
The new official forecast track has only minor adjustments from the 
previous forecast.

Some additional strengthening is expected during the next day or so 
as Elsa is expected to be in an environment of warm sea-surface
temperatures, light vertical wind shear, and high mid-level 
relative humidity.  However, as mentioned earlier, the fast forward 
motion could result in some decoupling of the lower and upper parts 
of the storm, and this could limit strengthening.  The latter part 
of the intensity forecast also has high uncertainty due to the 
possibility of land interaction and disagreements among the 
global models on how favorable the upper-level winds will be.  
Based on these factors, the NHC intensity forecast continues to be 
on the lower end of the intensity guidance suite.

Key Messages:
 
1. Tropical storm conditions are expected beginning early Friday in 
portions of the Windward and southern Leeward Islands.

2. Heavy rainfall from Elsa will move quickly across the Windward 
and southern Leeward Islands, including Barbados, on Friday, with 
outer rain bands impacting Puerto Rico Friday into Saturday. 
Isolated flash flooding and mudslides are possible.

3. There is a risk of wind and rainfall impacts in portions of 
Hispaniola, Cuba, the Turks and Caicos and the Bahamas through early 
next week.  Interests in these areas should monitor Elsa's progress 
and updates to the forecast.

4. There is a risk of storm surge, wind, and rainfall impacts in the 
Florida Keys and portions of the southern Florida Peninsula early 
next week. However, the forecast uncertainty remains larger than 
usual due to Elsa's potential interaction with the Greater Antilles 
this weekend. Interests in Florida should monitor Elsa's progress 
and updates to the forecast.


FORECAST POSITIONS AND MAX WINDS
 
INIT  01/1500Z 10.1N  51.4W   40 KT  45 MPH
 12H  02/0000Z 11.2N  54.9W   45 KT  50 MPH
 24H  02/1200Z 12.6N  59.9W   50 KT  60 MPH
 36H  03/0000Z 14.1N  64.9W   50 KT  60 MPH
 48H  03/1200Z 15.9N  69.8W   50 KT  60 MPH
 60H  04/0000Z 17.6N  73.6W   50 KT  60 MPH
 72H  04/1200Z 19.3N  76.5W   45 KT  50 MPH
 96H  05/1200Z 22.0N  80.5W   50 KT  60 MPH
120H  06/1200Z 25.6N  82.5W   50 KT  60 MPH
 
$$
Forecaster Beven
 
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