Tropical Storm ELSA Advisory zo, 04-07

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Tropical Storm Elsa Discussion Number  15
NWS National Hurricane Center Miami FL       AL052021
1100 PM EDT Sat Jul 03 2021

Elsa is undergoing a convective bursting pattern the past few
hours, with some cold overshooting tops of -90 deg C east and
northeast of the center. However, data from an Air Force Reserve
reconnaissance aircraft indicate that this convective increase has
not translated into an intensity increase. To the contrary, 5000-ft
flight-level and SFMR surface winds have decreased while the central
pressure has increased to 1004 mb. Based on the latest recon data,
the intensity has been lowered to 55 kt. The aircraft has now
climbed to 10,000 ft for safety reasons and will be penetrating the
area of intense convection to check for stronger winds there.

The initial motion estimate is now 295/15 kt.  Elsa is forecast to
gradually move around the western periphery of a deep-layer
subtropical ridge over the next 96 hours, accompanied by an
additional decrease in forward speed. The latest model guidance has
continued to converge along the previous advisory track, with the
corrected-consensus models HCCA and FSSE nearly on top of each
other. The TCVA simple consensus model is also similar to the HCCA
and FSSE models. However, out of respect for the slightly more
westward GFS and GFS-ensemble models, which have performed
admirably thus far with Elsa, the new official forecast lies a tad
west of the aforementioned consensus models and lies nearly on top
of the previous advisory track.

After interacting with the mountainous terrain of southwestern
Haiti, which could have caused some disruption in the low-level
field despite the center remaining offshore, little change in
intensity is expected tonight. However, some slight restrengthening
could occur by Sunday afternoon as Elsa approaches the south-central
coast of Cuba where the sea-surface temperatures are quite warm at
more than 30 deg C and the water is deep. Weakening is expected
after the cyclone moves across west-central Cuba, followed again by
some slight restrengthening after Elsa emerges over the warm Gulf
Stream in the Straits of Florida. Westerly vertical wind shear
increasing to near 20 kt by 96 hours should prevent any significant
strengthening from occurring. Elsa should become a very
asymmetrical tropical cyclone late on day 3 and on day 4 with most
of the heavy rain and strongest winds displaced along and to the
east of the forecast track. The initial intensity is similar to the
previous advisory and closely follows the simple and corrected
consensus models.

Given the remaining uncertainty in the track forecast and the degree
of land interaction with Hispaniola and Cuba, users are urged to
factor in some of this uncertainty.  For reference, average NHC
track errors at days 3 and 4 are 125 miles and 150 miles,
respectively.  The average NHC intensity errors are around 15 mph
for both days 3 and 4.

Key Messages:

1. Widespread heavy rain will move across southern Haiti and Jamaica
tonight into Sunday where isolated to scattered flash flooding and
mudslides will be possible. Heavy rain will then impact the Cayman
Islands and Cuba Sunday into Monday resulting in significant
flooding and mudslides over Cuba. As Elsa approaches the Florida
Keys and  Florida Peninsula early next week, isolated flash flooding
and minor river flooding will be possible.

2. Tropical storm conditions and dangerous storm surge are expected
with hurricane conditions possible in portions of eastern Cuba
beginning early Sunday, with tropical storm conditions possible in
central and western Cuba Sunday night and Monday.

3. There is an increasing risk of tropical storm conditions, storm
surge, and rainfall impacts beginning Monday in the Florida Keys and
the southern Florida Peninsula, and a Tropical Storm Watch is now
in effect for portions of the Florida Keys. This risk will spread
northward along the Florida Peninsula through Wednesday and reach
the coasts of Georgia and the Carolinas Wednesday and Thursday,
however uncertainty in the forecast remains larger than usual due
to Elsa's potential interaction with the islands of Hispaniola and
Cuba. Interests elsewhere in Florida and along the southeast U.S.
coast should monitor Elsa's progress and updates to the forecast.


FORECAST POSITIONS AND MAX WINDS

INIT  04/0300Z 17.9N  75.3W   55 KT  65 MPH
 12H  04/1200Z 19.2N  77.3W   55 KT  65 MPH
 24H  05/0000Z 20.9N  79.4W   60 KT  70 MPH
 36H  05/1200Z 22.5N  81.0W   50 KT  60 MPH...INLAND
 48H  06/0000Z 24.1N  82.2W   45 KT  50 MPH...OVER WATER
 60H  06/1200Z 26.0N  82.8W   50 KT  60 MPH
 72H  07/0000Z 28.0N  83.0W   50 KT  60 MPH
 96H  08/0000Z 32.7N  81.0W   45 KT  50 MPH...INLAND
120H  09/0000Z 37.7N  74.9W   35 KT  40 MPH...OVER WATER

$$
Forecaster Stewart/Papin