[Tropical] Tropical Cyclone Discussion

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WTNT44 KNHC 201456
TCDAT4

Tropical Depression Fourteen Discussion Number   1
NWS National Hurricane Center Miami FL       AL142020
1100 AM EDT Thu Aug 20 2020

Visible satellite images indicate that the area of disturbed
weather moving across the central Caribbean Sea has developed a
closed surface circulation, with the center embedded beneath
cellular convective cells and a large cirrus canopy.  Also,
convection has increased in organization, and TAFB and SAB have
given the system classification of T2.0/30 kt and T1.5/25 kt,
respectively.  Therefore, advisories are being initiated on
Tropical Depression Fourteen with maximum winds of 30 kt.  An
expected ASCAT pass later today and an Air Force Reserve Hurricane
Hunter mission scheduled for this afternoon should give us a better
handle on both the depression's center location and its maximum
winds.

The depression continues to move westward at a pretty good clip,
currently estimated to be on a heading of 280 degrees at 18 kt.
This motion is being driven by the western extent of the Bermuda
high, which currently noses into the northwestern Caribbean Sea.
However, a deep-layer trough over the Gulf of Mexico is expected to
become the main driver in the coming days, causing the cyclone to
slow down and turn rather suddenly toward the west-northwest and
northwest in the next 24-36 hours.  A general northwestward motion
should then continue until the end of the 5-day forecast period,
bringing the system across the Yucatan Peninsula Saturday night and
into the central and western Gulf of Mexico early next week.  Most
of the reliable track models are clustered close to one another,
and the official NHC track forecast is therefore very close to the
multi-model consensus aids, including the HCCA model.

Once the depression slows down during the next 24-36 hours,
environmental conditions appear ideal for strengthening.  The
magnitude of vertical shear is expected to be less than 10 kt for
at least the next 2 days, while the system will be moving over the
deep, warm waters of the northwestern Caribbean Sea, where sea
surface temperatures are 29-30 degrees Celsius.  Given these
conditions, some of the intensity guidance actually appears more
muted than I would have expected, and I have therefore elected to
closely follow the SHIPS and LGEM models, which are near the upper
end of the guidance envelope.  It is possible that the depression
could be near or at hurricane strength when it approaches the
Yucatan Peninsula of Mexico in 2-3 days.  Some weakening is
anticipated when the center moves over land, and then
re-strengthening is likely after it moves over the Gulf of Mexico.
There will be an increase in shear over the Gulf in 4-5 days, and
right now there is greater-than-normal uncertainty in how this will
affect the cyclone's intensity at that point.  For now, the
official forecast on days 4 and 5 shows a flat-lined intensity, and
this scenario lies a little above the ICON intensity consensus and
the HCCA model solution.

Key Messages:

1. Tropical Depression Fourteen is expected to strengthen over the
northwestern Caribbean Sea through Saturday, and it could produce
tropical-storm-force winds and heavy rainfall over portions of the
coast of Honduras and 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 later today.

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  20/1500Z 15.1N  79.7W   30 KT  35 MPH
 12H  21/0000Z 15.5N  81.9W   35 KT  40 MPH
 24H  21/1200Z 16.3N  84.2W   40 KT  45 MPH
 36H  22/0000Z 17.1N  85.5W   50 KT  60 MPH
 48H  22/1200Z 18.4N  86.4W   55 KT  65 MPH
 60H  23/0000Z 19.9N  87.4W   60 KT  70 MPH
 72H  23/1200Z 21.5N  88.9W   45 KT  50 MPH
 96H  24/1200Z 25.0N  92.0W   50 KT  60 MPH
120H  25/1200Z 28.0N  94.0W   50 KT  60 MPH

$$
Forecaster Berg
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