[Tropical] Tropical Cyclone Discussion

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WTNT44 KNHC 211456
TCDAT4

Tropical Depression Fourteen Discussion Number   5
NWS National Hurricane Center Miami FL       AL142020
1100 AM EDT Fri Aug 21 2020

An Air Force Reserve Hurricane Hunter aircraft flew into the
depression a few hours ago, and the plane made two center fixes
that were about 35 n mi apart, indicating that there are likely
multiple low-level swirls rotating around a common center.  A
well-defined swirl coincident with the second center fix has become
apparent in visible satellite imagery, but for now a blend of the
aircraft fixes is being used for the initial position until we can
be sure the satellite feature is in fact the one and only center.
Flight-level and SFMR winds, outside of heavy rainfall, indicate
that the maximum winds remain 30 kt.  Deep convection is still
lacking in organization, with the heaviest activity well to the
north near the Cayman Islands and along the Honduras coast.

The depression is moving northwestward, or 305/12 kt, along the
southwestern periphery of an Atlantic subtropical ridge and toward
a deep-layer trough over the Gulf of Mexico.  This northwestward
motion is expected to persist for the entire 5-day forecast period,
with a decrease in forward speed anticipated while the cyclone
approaches the Yucatan coast.  The track guidance has slowed down a
bit during that time, especially the GFS, and the new NHC forecast
is therefore a little slower than the previous forecast.  After
that time, an increase in forward speed is expected, and the NHC
forecast lies to the west of the TVCN model consensus, closer to
the GFS, ECMWF, and HCCA scenarios.

The structure of the depression aside, the environment still
appears conducive for strengthening while the system approaches the
Yucatan Peninsula.  Vertical shear over the depression is currently
less than 10 kt and is expected to remain low for the next 36-48
hours, and sea surface temperatures will be around 30 degrees
Celsius.  Therefore, steady intensification is shown in the official
forecast through 36 hours, and the NHC prediction lies near the
upper end of the guidance envelope between the HCCA and HWRF
solutions just before the center reaches the Yucatan coast.  After
some weakening while over the Yucatan Peninsula, re-intensification
is likely to occur over the central Gulf of Mexico between days 2
and 3 while vertical shear remains relatively low, and the cyclone
could become a hurricane during that time, as shown by the HCCA,
HWRF, and HMON models.  After day 3, southwesterly vertical shear of
30 kt or more is expected to develop over the northwestern Gulf, and
the official forecast follows the trend of all the intensity
guidance, showing weakening by day 4 as the cyclone approaches the
southeastern Texas or southwestern Louisiana coastline.  This
forecast remains highly uncertain, however, and users are urged to
continue monitoring changes to this forecast over the next couple
of days.


Key Messages:

1.  Heavy rainfall and gusty winds over portions of the coasts of
Nicaragua and Honduras, including the Bay Islands, are expected to
diminish today.

2. Tropical Depression Fourteen is expected to strengthen over the
northwestern Caribbean Sea through Saturday, and it is expected to
be near or at hurricane strength when it reaches the east coast of
the Yucatan Peninsula of Mexico late Saturday.  A Hurricane Watch
and a Tropical Storm Warning are in effect for portions of that
region.

3. 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 central 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  21/1500Z 16.6N  84.1W   30 KT  35 MPH
 12H  22/0000Z 17.4N  85.0W   40 KT  45 MPH
 24H  22/1200Z 18.6N  85.9W   50 KT  60 MPH
 36H  23/0000Z 20.0N  86.9W   60 KT  70 MPH
 48H  23/1200Z 21.5N  88.2W   50 KT  60 MPH...INLAND
 60H  24/0000Z 23.2N  89.7W   55 KT  65 MPH...OVER WATER
 72H  24/1200Z 25.1N  91.4W   65 KT  75 MPH
 96H  25/1200Z 28.7N  94.1W   60 KT  70 MPH
120H  26/1200Z 31.3N  95.5W   40 KT  45 MPH...INLAND

$$
Forecaster Berg
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