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Tropical Depression Nineteen Discussion Number 3
NWS National Hurricane Center Miami FL AL192020
500 AM EDT Sat Sep 12 2020
Surface observations and Doppler radar data indicate that Tropical
Depression Nineteen was close to tropical storm strength when it
moved ashore in Miami-Dade county just after 06Z. The central
pressure had dropped to near 1004 mb, and the radar showed winds of
45-50 kt above the surface just to the northeast of the center,
associated with a strong convective burst. However, there were no
surface observations of 35-kt sustained winds, and the highest
reported gusts were in the 35-40 kt range. Based on the available
data, the initial intensity remains 30 kt. It should be noted
that since landfall, the strong convective burst near the
low-level center has weakened considerably.
The cyclone has turned left during the past several hours, and the
initial motion is a somewhat uncertain 270/8 kt. The subtropical
ridge extending from the southeastern United States eastward over
the Atlantic should steer the cyclone generally west-northwestward
through Sunday. After that time, the ridge is forecast to weaken
due to an approaching mid-latitude trough. This should result in a
northwestward motion through from Sunday night into the middle
portion of next week, with the cyclone expected to reach the
northern Gulf coast around the 96 h point. The latest track
guidance now has the cyclone responding more strongly to the trough
and turning northward by 120 h. The new forecast track is shifted
a little south of the previous track through 72 h based on the
initial position and motion. At 120 h, the new track is nudged to
the east of the old track, but it still lies to the west of the
consensus models.
The depression is currently experiencing some northerly vertical
wind shear, and the latest global model runs are showing more shear
affecting the system as it crosses the Gulf of Mexico than earlier.
However, since the cyclone is going to be over very warm sea
surface temperatures and in a moist environment, the intensity
guidance still shows it strengthening to near hurricane strength,
or stronger, before it reaches the northern Gulf coast. Due to the
uncertainty about the amount of shear, the new intensity forecast
has only minor adjustments from the previous forecast. However,
it lies below the various intensity consensus models.
Users are reminded to not to focus on the exact details of the
track or intensity forecast as the average NHC track error at 96 h
is around 150 miles and the average intensity error is around
15 mph. In addition, winds, storm surge, and rainfall hazards will
extend far from the center.
KEY MESSAGES:
1. Tropical Depression Nineteen is expected to produce isolated to
scattered flash flooding across portions of west-central and
southern Florida and prolong existing minor river flooding across
Central Florida through Sunday. Scattered flash flooding is also
possible across portions of the central Gulf Coast Sunday through
Tuesday morning.
2. Tropical storm conditions are possible by Sunday night in
portions of the Florida Panhandle, where a Tropical Storm Watch has
been issued. Wind gusts to tropical-storm force could occur over
portions of the southern Florida Peninsula today.
3. The system is forecast to strengthen to near hurricane intensity
by early next week as it moves across the northeastern Gulf of
Mexico. Dangerous impacts from storm surge, wind, and heavy rainfall
will be possible along the Gulf Coast from the Florida Panhandle to
southeastern Louisiana late this weekend and early next week.
Residents in these areas should monitor the progress of this system
and updates to the forecast, as Storm Surge, Tropical Storm or
Hurricane watches could be issued later today.
FORECAST POSITIONS AND MAX WINDS
INIT 12/0900Z 25.6N 80.7W 30 KT 35 MPH...INLAND
12H 12/1800Z 26.1N 82.0W 30 KT 35 MPH...OVER WATER
24H 13/0600Z 26.9N 83.8W 35 KT 40 MPH
36H 13/1800Z 27.9N 85.4W 40 KT 45 MPH
48H 14/0600Z 28.7N 86.6W 50 KT 60 MPH
60H 14/1800Z 29.3N 87.7W 60 KT 70 MPH
72H 15/0600Z 29.6N 88.5W 60 KT 70 MPH
96H 16/0600Z 30.5N 90.0W 55 KT 65 MPH...INLAND
120H 17/0600Z 31.5N 90.5W 25 KT 30 MPH...INLAND
$$
Forecaster Beven
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