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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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