[Tropical] Tropical Cyclone Discussion

[EMWIN Server]

WTNT41 KNHC 131455
TCDAT1

Tropical Depression Thirty-One Discussion Number   1
NWS National Hurricane Center Miami FL       AL312020
1100 AM EDT Fri Nov 13 2020

Deep convection associated with the area of low pressure over the
central Caribbean Sea has increased and become more concentrated
since yesterday. One-minute GOES-16 visible satellite imagery shows
that the circulation has also become better defined, with a westerly
component seen in the low-cloud motion near the southwestern edge
of the primary convective mass.  Subjective Dvorak intensity
estimates from both TAFB and SAB are T2.0, indicating that the
convection has become sufficiently organized for the system to be
classified as a tropical depression.  The initial wind speed is set
at 30 kt, in line with the Dvorak classifications.

Environmental conditions of low vertical wind shear, warm sea
surface temperatures, and a moist atmosphere favor intensification
over the next few days.  Given the current broad and sprawling
structure of the system, strengthening may begin as gradual today,
but once an inner core organizes, steady-to-rapid strengthening
appears likely. While the SHIPS rapid intensification index does not
show very high chances of rapid strengthening for any one 24-h
period over the next few days, it does indicate a 50/50 chance
(nearly 10 times the climatological mean) of a 65-kt increase in
wind speed over the next 72 hours.  As a result, the NHC forecast
calls for significant strengthening during the 24 to 72 hour time
period, and the system could approach the coast of Central America
as a major hurricane in a few days.  The NHC track forecast at days
4 and 5 shows the system weakening over land, however some of the
track guidance keeps the system just off the coast on Honduras at
that time.  If a more northern track occurs, the system could be
stronger at 96 and 120 h if it remains over water.

The depression is moving west-southwestward at about 6 kt. A strong
mid-level ridge that lies over Florida and the western Atlantic
should steer the cyclone west-southwestward during the next 12 to 24
hours.  After that time, the ridge is forecast to begin sliding
eastward, and a westward to west-northwestward motion should begin.
On the foreast track, the cyclone is expected to approach the
coast of Central America in 60-72 h.  The track guidance is in good
agreement through the first couple of days, but there is increasing
cross-track spread after that time.  The HMON, HWRF, and GFS show a
track near or north of the coast of Honduras after 72 hours, while
the ECMWF and UKMET are farther south. For now, the NHC track is
near the middle of the guidance envelope between the HFIP corrected
consensus model and the TCVA multi-model consensus.

Key Messages:

1. The depression is expected to strengthen to a hurricane while it
approaches the coast of Central America, and there is a risk of
dangerous wind, storm surge, and rainfall impacts across portions of
Nicaragua and Honduras beginning Sunday night. Hurricane Watches
will likely be issued for a portion of this area tonight.

2. Through Wednesday morning, heavy rainfall from Tropical
Depression Thirty-One may lead to life-threatening flash flooding
and river flooding across portions of Haiti, Jamaica and Central
America.  Flooding and landslides from heavy rainfall could be
significant across Central America given recovery efforts underway
after Hurricane Eta.


FORECAST POSITIONS AND MAX WINDS

INIT  13/1500Z 14.2N  74.3W   30 KT  35 MPH
 12H  14/0000Z 14.0N  75.0W   35 KT  40 MPH
 24H  14/1200Z 13.8N  76.0W   45 KT  50 MPH
 36H  15/0000Z 13.9N  77.3W   60 KT  70 MPH
 48H  15/1200Z 14.1N  79.0W   70 KT  80 MPH
 60H  16/0000Z 14.5N  80.9W   85 KT 100 MPH
 72H  16/1200Z 14.9N  82.7W   95 KT 110 MPH
 96H  17/1200Z 15.2N  85.7W   50 KT  60 MPH...INLAND
120H  18/1200Z 14.7N  88.3W   25 KT  30 MPH...POST-TROP/REMNT LOW

$$
Forecaster Brown
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