[Tropical] Tropical Cyclone Discussion

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WTNT44 KNHC 202057
TCDAT4

Tropical Depression Fourteen Discussion Number   2
NWS National Hurricane Center Miami FL       AL142020
500 PM EDT Thu Aug 20 2020

An Air Force Reserve Hurricane Hunter aircraft investigating the
system found an area of lighter winds--likely where the center would
be--farther south than previous estimates.  The highest flight-level
wind measured by the aircraft was 30 kt at an altitude of 2500 feet,
and although there were some SFMR measurements over 40 kt, these
looked coincident with some heavy rain rates and thus are probably
not reliable. Therefore, the initial intensity remains 30 kt.
Structurally, the depression has a large cloud envelope with
sporadic convective cells located in loose bands.

The updated initial position derived from the aircraft data
indicates that the current motion is still westward, or 270/16 kt.
This southward adjustment really only affected the first 36 hours
or so of the forecast, with NHC's official track forecast being
shifted southward during that period.  This ends up taking the
cyclone's center over extreme northern Nicaragua and northeastern
Honduras in 12-24 hours.  After 36 hours, model guidance remains in
good agreement that the system should turn northwestward due to a
deep-layer trough over the Gulf of Mexico.  The new set of model
guidance has not shifted much from the previous cycle, and the NHC
track forecast is very close to the morning forecast despite the
initial position adjustment, with perhaps a slight eastward shift
on days 4 and 5.  In general, the NHC forecast is closest to the
GFS and HCCA model solutions.

The depression's farther-south position makes the intensity
forecast more complicated with potentially more land interaction
with parts of Central America.  Slight strengthening to tropical
storm strength is expected before the center reaches Honduras and
Nicaragua, with little change thereafter until the center
re-emerges over the Gulf of Honduras.  Low shear and warm sea
surface temperatures should then support further intensification up
until it reaches the Yucatan Peninsula.  Since there is significant
uncertainty in how land interaction will affect the cyclone's
intensity, the forecast intensity has been flat-lined between day 2
and day 4, with the understanding that the the winds could increase
or decrease from the value shown.  Vertical shear is expected to
increase by day 5, and some weakening is shown at that time.

Key Messages:

1. Tropical Depression Fourteen is expected to strengthen over the
northwestern Caribbean Sea through Saturday, and is likely to
produce tropical-storm-force winds and heavy rainfall over portions
of the coasts of Nicaragua and Honduras, including the Bay Islands,
beginning tonight through Friday.  The system could be near or at
hurricane strength when it reaches the Yucatan Peninsula of Mexico
late Saturday, and watches could be required for a portion of that
area tonight.

2. The system is expected to move into the south-central Gulf
of Mexico as a tropical storm on Sunday.  Some strengthening is
anticipated while it moves northwestward over the western Gulf of
Mexico early next week, but it is too soon to know exactly how
strong it will get or the location and magnitude of impacts it
will produce along the central or northwestern Gulf Coast.
Interests in that area should continue monitoring the progress of
this system over the next few days.

FORECAST POSITIONS AND MAX WINDS

INIT  20/2100Z 14.3N  81.0W   30 KT  35 MPH
 12H  21/0600Z 14.7N  83.0W   35 KT  40 MPH
 24H  21/1800Z 15.6N  84.7W   35 KT  40 MPH...INLAND
 36H  22/0600Z 17.0N  85.6W   45 KT  50 MPH...OVER WATER
 48H  22/1800Z 18.7N  86.6W   55 KT  65 MPH
 60H  23/0600Z 20.3N  87.9W   55 KT  65 MPH...INLAND
 72H  23/1800Z 22.1N  89.2W   55 KT  65 MPH...OVER WATER
 96H  24/1800Z 26.0N  91.5W   55 KT  65 MPH
120H  25/1800Z 28.5N  93.5W   50 KT  60 MPH

$$
Forecaster Berg
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