[Tropical] Tropical Cyclone Discussion

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WTNT44 KNHC 050238
TCDAT4

Tropical Depression Eta Discussion Number  18
NWS National Hurricane Center Miami FL       AL292020
900 PM CST Wed Nov 04 2020

The rugged terrain of Central America is taking a toll on Eta.  The
low-level circulation is losing definition, and deep convection is
well removed from the center.  Eta was downgraded to a 30-kt
tropical depression a few hours ago, and the initial intensity is
held at that value for this advisory.  The strongest winds are
likely occurring offshore over the Gulf of Honduras, as noted in
earlier ASCAT scatterometer surface wind data.

Eta, or its remnant low, is forecast to move west-northwestward to
northwestward during the next 12 to 24 hours, taking the cyclone
across portions of Honduras during that time.  In 24 to 36 hours, a
turn to the north and then northeast is forecast as Eta feels some
influence from a mid- to upper level trough moving over the
northwestern Gulf of Mexico.  As this trough slides southeastward
across the Gulf, it should steer Eta northeastward at a faster
forward speed toward Cuba, likely approaching that country late
Saturday or Sunday.  After that time, the models show Eta rotating
around the north side of the trough (or cut-off low) in the
vicinity of south Florida and the Florida Keys late this weekend and
early next week. There is still a lot of spread in the model tracks
at the 96- and 120-hour time periods, which is not surprising given
the expected complex steering pattern.   The NHC track forecast is
adjusted a little to the east of the previous one to come into
better agreement with the latest models, but confidence in the
details of the extended track forecast is low.

Continued weakening is expected while Eta remains inland over the
rugged terrain of Central America, and the cyclone will likely
degenerate into a remnant low or trough of low pressure on Thursday.
Whatever is left of Eta, and the broad gyre that it is embedded
within, will move offshore of Belize over the northwestern Caribbean
Sea by Thursday night or Friday. The rate of intensification over
the northwestern Caribbean Sea will likely be gradual because of the
mixed environmental conditions.  On one hand, Eta will be moving
over warm water and in a region of upper-level diffluence, which
should support convective growth and strengthening.  Conversely,
there will also be an increase in wind shear and the cyclone is
likely to have a broad structure, which should prevent rapid
intensification.  The net result will likely be slow but steady
strengthening, and Eta is forecast to be a strong tropical storm
when it is near south Florida.  The models are in fair agreement on
Eta's future intensity, and this forecast is just a little higher
than the previous one.

Key Messages:

1. Through Monday morning, heavy rainfall from Eta will lead to
catastrophic, life-threatening flash flooding and river flooding
across portions of Central America, along with landslides in areas
of higher terrain.  Flash and river flooding is also possible across
Jamaica, southeast Mexico, the Cayman Islands and western Cuba.

2. Eta is forecast to regain tropical storm strength over the
northwestern Caribbean Sea late this week. Although the details of
the future track and intensity of Eta are uncertain, there is an
increasing risk of impacts from wind and rainfall in portions of
Cuba, southern Florida and the Florida Keys this weekend and early
next week.


FORECAST POSITIONS AND MAX WINDS

INIT  05/0300Z 14.2N  86.3W   30 KT  35 MPH...INLAND
 12H  05/1200Z 15.0N  87.3W   25 KT  30 MPH...POST-TROP/REMNT LOW
 24H  06/0000Z 16.1N  87.8W   25 KT  30 MPH...POST-TROP/REMNT LOW
 36H  06/1200Z 17.2N  86.8W   30 KT  35 MPH...POST-TROP/REMNT LOW
 48H  07/0000Z 18.2N  85.5W   35 KT  40 MPH...TROPICAL CYCLONE
 60H  07/1200Z 19.3N  83.7W   40 KT  45 MPH
 72H  08/0000Z 20.4N  82.0W   45 KT  50 MPH
 96H  09/0000Z 23.3N  79.9W   50 KT  60 MPH
120H  10/0000Z 24.7N  81.4W   55 KT  65 MPH

$$
Forecaster Cangialosi
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