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Hurricane ELSA

Hurricane Elsa Discussion Number  11
NWS National Hurricane Center Miami FL       AL052021
1100 PM AST Fri Jul 02 2021
Data from an Air Force Reserve hurricane hunter aircraft indicate 
that Elsa has weakened slightly, and that the flight-level and 
surface centers are not vertically aligned. The maximum 700-mb wind 
speed measured was 75 kt and the highest SFMR surface wind sampled 
was 61 kt in the northeastern quadrant. However, these data were 
collected outside of the strongest convection that was occurring 
just east of the flight track, so the intensity has only been 
lowered to 70 kt, which is supported by the slightly higher central 
pressure of 995 mb sampled by a dropsonde.
The initial motion estimate now is 285/25 kt.  There remains little 
significant change to the previous track forecast or reasoning. The 
latest 00Z model guidance has become more convergent and now lies 
nearly on top of the previous advisory track. Over the last 48 h, 
the ECMWF model has steadily shifted Elsa's track westward by about 
1 degree of longitude each model cycle, with the latest ECMWF 
forecast track now being located about 240 nmi west of its forecast 
track two days ago. As a result, less weight has been placed on the 
ECMWF solution for this advisory. However, even its latest solution 
no longer takes Elsa over the heart of Hispaniola. Elsa should 
continue to move generally west-northwestward for the next 48 h, 
accompanied by a slow but steady decrease in forward speed. By the 
time the hurricane nears southern Cuba, the forward speed should be 
less than 15 kt. Thereafter, Elsa should gradually turn 
northwestward and eventually northward through a developing weakness 
in the subtropical ridge This motion should take Elsa across Cuba 
and over the eastern Gulf of Mexico or the nearby Florida Peninsula 
on day 4, followed by a motion over the coastal regions of the 
southeastern United States on day 5. The new NHC forecast track is 
essentially just an update of the previous advisory, and closely 
follows a blend of the GFS, UKMET, and HWRF models, and the TVCA 
simple consensus model.

Elsa's fast forward speed and recent entrainment of dry mid-level 
air into the western semicircle has eroded some of the inner-core 
convection, resulting in the aforementioned weakening. In fact, NOAA 
G-IV dropsondes launched around 2100 UTC northwest of Elsa indicated 
a significant dry-air layer between 400-500-hPa that may have 
been imported by moderate northwesterly mid-level shear. However, as 
the cyclone's forward speed steadily decreases, the low-, mid-, and 
upper-level circulations should become more vertically aligned, 
which should allow for at least some slight re-strengthening during 
the next 24 h or so. Possible interaction with the landmasses of 
Haiti, southeastern Cuba, and Jamaica is the primary reason for not 
showing a more robust intensity forecast given the very warm water 
beneath the hurricane and a very favorable upper-level wind flow 
regime. The latest GFS and UKMET models indicate that Elsa will be 
moving into the center of a 300-200-mb synoptic-scale anticyclone, 
which would produce enhanced outflow jets to the north and south of 
the cyclone, resulting in significant strengthening. If Elsa ends up 
'threading-the-needle' between Haiti, Jamaica, and Cuba, then 
subsequent intensity forecasts may have to be increased similar to 
the much stronger HWRF model. For now, the official NHC intensity 
forecast maintains continuity with the previous advisory, and shows 
only slight re-strengthening due to possible interaction with land.
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. The outer rain bands from Elsa will impact Puerto Rico by late 
tonight, with widespread heavy rain moving into southern Hispaniola 
and Jamaica Saturday into Sunday. Isolated to scattered flash 
flooding and mudslides are possible. Through early next week, heavy 
rain is expected to impact the Cayman Islands and Cuba resulting in 
significant flooding with mudslides possible in Cuba. 
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.
INIT  03/0300Z 14.8N  66.3W   70 KT  80 MPH
 12H  03/1200Z 16.1N  69.8W   70 KT  80 MPH
 24H  04/0000Z 17.6N  73.5W   75 KT  85 MPH
 36H  04/1200Z 19.0N  76.2W   75 KT  85 MPH
 48H  05/0000Z 20.5N  78.5W   70 KT  80 MPH
 60H  05/1200Z 22.1N  80.4W   55 KT  65 MPH...INLAND
 72H  06/0000Z 23.7N  81.7W   55 KT  65 MPH...OVER WATER
 96H  07/0000Z 27.7N  82.9W   50 KT  60 MPH
120H  08/0000Z 32.4N  80.7W   35 KT  40 MPH...INLAND
Forecaster Stewart/Papin