[Tropical] Tropical Cyclone Discussion

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WTNT45 KNHC 032053
TCDAT5

Tropical Storm Elsa Discussion Number  14
NWS National Hurricane Center Miami FL       AL052021
500 PM EDT Sat Jul 03 2021

Satellite imagery shows that Elsa looks ragged and disorganized at
this time, with bursts of convection occuring near the low-level
center and poorly-defined convective banding.  Some of this is
likely due to the the proximity of the system to Hispaniola.  Air
Force Reserve and NOAA Hurricane Hunter aircraft have reported
reliable 55-60 kt surface wind estimates from the SFMR, along with
the latest central pressure report of 1000 mb.  The initial
intensity remains 60 kt based mainly on the SFMR data.

The initial motion is now 295/24.  There is little change in
the forecast philosophy from the previous advisory.  Elsa is
approaching a weakness in the subtropical ridge caused by a large
baroclinic trough over the eastern United States.  The global
models forecast this trough to move eastward into the Atlantic, but
the southern portion is likely to split off and become an
upper-level low pressure area over the western Gulf of Mexico, with
the subtropical ridge over the Atlantic situated to the east of the
this low.  In response, Elsa should slow its forward motion and
turn northwestward during the next 48 h, followed by a general
northward motion from 60-96 h and recurvature into the westerlies
after that time.  The forecast track takes the center near or over
southwestern Haiti, Cuba, and the eastern Gulf of Mexico or the
Florida Peninsula during the next 3 days or so.  After that, the
system is likely to cross portions of the southeastern United
States on its way into the Atlantic.  The new forecast track is
changed little from the previous advisory, and it lies near the
center of the now reasonably-agreeing track guidance envelope.

In addition to land interaction, Elsa continues to be affected by
northwesterly shear that is at least partly due to the fast
low-level flow that the storm is embedded in.  Some shear is
expected to continue through the next 72 h.  However, once the
system passes the southwestern peninsula of Haiti, there may be less
land interaction than previously forecast. The intensity guidance is
in good agreement on weakening during the next 48 h, and the GFS,
UKMET, and ECMWF show Elsa as a not very vertically aligned system
with some separation between the low- and mid-level centers over
the southeastern Gulf of Mexico.  After that, despite the shear,
upper-level divergence associated with the aforementioned
upper-level low could allow for some re-intensification as forecast
by the HWRF and other models.  The new NHC intensity forecast calls
for some weakening in the first 48 h and then shows re-
intensification over the Gulf of Mexico.  Through the first 72 h,
the forecast remains at the upper edge of the intensity guidance.

Hurricane warnings remain in effect for portions of Haiti at this
time, as there is still the possibility that a short-lived
re-intensification might occur due to a convective burst.

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. A hurricane warning remains in effect for portions of Haiti,
where near-hurricane conditions and dangerous storm surge are
expected through this evening.

2. Widespread heavy rain will move across southern Hispaniola 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.

3. 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.

4. 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  03/2100Z 17.5N  73.9W   60 KT  70 MPH
 12H  04/0600Z 18.7N  75.9W   60 KT  70 MPH
 24H  04/1800Z 20.2N  78.3W   60 KT  70 MPH
 36H  05/0600Z 21.6N  80.1W   55 KT  65 MPH
 48H  05/1800Z 23.1N  81.6W   45 KT  50 MPH
 60H  06/0600Z 24.9N  82.6W   50 KT  60 MPH
 72H  06/1800Z 26.9N  83.1W   55 KT  65 MPH
 96H  07/1800Z 32.0N  82.0W   45 KT  50 MPH...INLAND
120H  08/1800Z 36.5N  77.0W   35 KT  40 MPH...INLAND

$$
Forecaster Beven
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