[Tropical] Tropical Cyclone Discussion

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WTNT45 KNHC 012047
TCDAT5

Tropical Storm Elsa Discussion Number   5
NWS National Hurricane Center Miami FL       AL052021
500 PM AST Thu Jul 01 2021

The structure of Elsa has changed little since the last advisory,
with the low-level center partly exposed to the northwest of the
somewhat-ragged primary convective band.  Various subjective and
objective satellite intensity estimates have changed little during
the last 6 h, so the initial intensity is held at 40 kt.

The initial motion is now 285/25.  There is little change to the
track forecast philosophy from the previous advisory.  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 the ECMWF ensembles forecast a turn toward the north
while the GFS and UKMET are forecasting a continued west-
northwestward to northwestward motion.  In addition, the GFS
ensemble members are spread from a continued west-northwestward
motion toward the Yucatan Peninsula on one side to a northward
motion east of the northern Bahamas on the other.  The latter part
of the new NHC forecast track will still lean more toward the
deterministic GFS/UKMET solutions, but the confidence remains low.
The new official forecast track again has only minor adjustments
from the previous forecast.

The intensity forecast and its high uncertainty are also little
changed from the last advisory.  Some 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 the upper and lower
parts of the storm being unable to stay together, and this could
limit strengthening.  The latter part of the intensity forecast also
has the issues of possible land interaction and disagreements among
the global models on how favorable the upper-level winds will be,
although the latest model runs trended toward less favorable
conditions north of about 22N.  This uncertainty is highlighted by
the UKMET forecasting Elsa to weaken to a trough near western Cuba
while the GFS forecasts it to be a hurricane in the same area and
time. 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, and are
possible over portions of southern Hispaniola on Saturday.

2. Heavy rainfall from Elsa will move quickly across the Windward
and southern Leeward Islands, including Barbados, on Friday. Outer
rain bands will impact Puerto Rico on Friday and southern Hispaniola
by early Saturday. Flooding and mudslides are possible.

3. There is a risk of wind and rainfall impacts in portions of
Cuba, Jamaica, 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 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  01/2100Z 11.2N  53.8W   40 KT  45 MPH
 12H  02/0600Z 12.1N  57.5W   45 KT  50 MPH
 24H  02/1800Z 13.5N  62.4W   50 KT  60 MPH
 36H  03/0600Z 15.1N  67.3W   50 KT  60 MPH
 48H  03/1800Z 16.7N  71.6W   50 KT  60 MPH
 60H  04/0600Z 18.3N  75.0W   50 KT  60 MPH
 72H  04/1800Z 19.8N  77.9W   50 KT  60 MPH
 96H  05/1800Z 22.5N  82.0W   50 KT  60 MPH
120H  06/1800Z 26.5N  83.5W   50 KT  60 MPH

$$
Forecaster Beven
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