Tropical Depression Fourteen Forecast Discussion

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WTNT44 KNHC 210258
TCDAT4

Tropical Depression Fourteen Discussion Number   3
NWS National Hurricane Center Miami FL       AL142020
1100 PM EDT Thu Aug 20 2020

The overall convective pattern has improved somewhat since the 
previous advisory, with a band of deep convection having developed 
near and just south of the low-level center. A pronounced mid-level 
circulation has been rotating westward to the north of the center of
the broader low-level circulation, which has likely prevented the 
cyclone from becoming a tropical storm by now, especially given the 
very impressive outflow pattern. However, NOAA buoy 42057 to the 
north of the center recently reported a sustained wind of 29 kt at 
4 meters elevation, which equals about a 32-kt 10-meter wind speed, 
which means that the cyclone isn't far from becoming a tropical 
storm. The intensity is being maintained at 30 kt until convection 
becomes more persistent.

The center has been reforming a little farther north and has also 
slowed down, with the initial motion now being west-northwestward 
or 285/12 kt. The slower and farther north initial position has 
required a slight northward shift in the forecast track for the 
next 24 hours and, as a result, the center of the cyclone is no 
longer expected to make landfall very far inland over Honduras or 
Nicaragua, if it makes landfall at all. By 36 hours, the new NHC 
forecast track shifts back closer to the previous advisory track 
due to a strong mid-level ridge extending westward across Florida 
and into the eastern and central Gulf of Mexico. That feature is 
expected to keep the cyclone moving in a general northwestward 
direction on days 2-5, resulting in landfall over the northeastern 
Yucatan Peninsula on Saturday, and be approaching the northwestern 
Gulf coast by the middle of next week. The official forecast track 
lies along the southern edge of the guidance envelope, close to the 
middle of the simple consensus models and a little south of the 
NOAA-HCCA corrected model.

Due to the northward shift in the new forecast track, the center 
and inner-core wind field of the cyclone will not be disrupted as 
much as previously expected, which has significant implications in 
the intensity forecast. The depression is now expected to reach 
hurricane strength just before it makes landfall on the east side 
of the Yucatan Peninsula in about 48 hours. Weakening is forecast 
in 60 hours while the cyclone moves across northeastern Yucatan, 
followed by gradual re-strengthening thereafter. Ocean temperatures 
along the path of the cyclone are forecast to be 30.0-30.5 deg C 
and the vertical shear is expected to remain low at less than 10 kt 
through 96 hours. Those conditions coupled with the impressive 
outflow pattern should allow for at least typical strengthening. By 
120 hours, the GFS- and ECMWF-based SHIPS models show the vertical 
wind shear increasing sharply from the southwest to 20-25 kt, which 
would normally induce weakening. However, it appears that those 
models are incorporating some strong jetstream winds of 60-70 kt 
well to the northwest of the center of the cyclone, which has 
resulted in high bias in the shear output. Therefore, the cyclone 
is forecast to be near hurricane strength when it approaches the 
Texas coast in 120 hours. The new intensity forecast is similar to 
but a little higher then the previous advisory due to less land 
interaction than previously expected, and is is a blend of the 
Decay-SHIPS and LGEM models, which are at the upper-end of the 
guidance envelope.

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 is expected be near 
or at hurricane strength when it reaches the Yucatan Peninsula of 
Mexico late Saturday where a Hurricane Watch and a Tropical Storm 
Warning are in effect.

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  21/0300Z 14.9N  82.2W   30 KT  35 MPH
 12H  21/1200Z 15.5N  83.8W   35 KT  40 MPH
 24H  22/0000Z 16.8N  85.1W   45 KT  50 MPH
 36H  22/1200Z 18.2N  86.0W   55 KT  65 MPH
 48H  23/0000Z 19.8N  87.2W   65 KT  75 MPH
 60H  23/1200Z 21.4N  88.5W   40 KT  45 MPH...INLAND
 72H  24/0000Z 23.2N  89.8W   50 KT  60 MPH...OVER WATER
 96H  25/0000Z 26.7N  92.3W   65 KT  75 MPH
120H  26/0000Z 29.1N  94.3W   65 KT  75 MPH

$$
Forecaster Stewart



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