[Tropical] Tropical Cyclone Discussion

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WTNT43 KNHC 221452
TCDAT3

Tropical Storm Laura Discussion Number  11
NWS National Hurricane Center Miami FL       AL132020
1100 AM AST Sat Aug 22 2020

Laura is producing considerable deep convection but the cloud
pattern remains disorganized.  Surface observations indicate that
the center is still not well defined, but the San Juan WSR-88D radar
shows a mid-level center south of eastern Puerto Rico.  The radar
also shows heavy rains spreading over that island.  The initial
intensity estimate remains at 35 kt based on continuity. As noted in
previous discussions, the intensity forecast for Laura is dependent
on its future track.  The official forecast, like the previous one,
moves the center over the land masses of Hispaniola and Cuba for the
next couple of days which should limit intensification at least
through the weekend.  After Laura moves into the Gulf of Mexico,
warm waters should lead to strengthening and the system is likely to
become a hurricane in 3 to 4 days.  The official intensity forecast
is close to the consensus guidance.  At this time the influence of
small tropical cyclone Marco, which should move over the
northwestern Gulf about a day or two before Laura, is not expected
to be significant.  This could change in the coming days however.

The initial motion estimate remains quite uncertain and is near
280/16 kt.  No significant changes are being made to the official
track forecast.  Laura is likely to move on a generally
west-northwestward track on the periphery of a mid-tropospheric high
pressure area for the next few days.  By day 4, the system should
turn northwestward while moving along the southwestern side of the
high.  The official track forecast is only slightly north of the
dynamical model consensus at 36-72 hours and essentially the same as
the consensus otherwise.  The GFS and its ensemble mean are
significantly farther west of the official forecast at days 3 and
beyond, which suggests relatively low confidence in the longer-range
track of Laura.

Key Messages:

1. Tropical storm conditions are expected across portions of the
the Virgin Islands and Puerto Rico today.  Tropical storm
conditions are also expected along the northern coasts of the
Dominican Republic and Haiti, and the Turks and Caicos and
southeastern Bahamas Saturday into Sunday.  Heavy rainfall is
likely across these areas and could cause mudslides and flash and
urban flooding through Sunday, with widespread river flooding
possible in Puerto Rico.

2. Tropical storm conditions are possible over portions of the
central Bahamas Sunday night, as well as portions of eastern
and central Cuba Sunday and Sunday night.

3. The details of the long-range track and intensity forecasts
remain more uncertain than usual since Laura is forecast to move
near or over portions of the Greater Antilles through Monday.
However, Laura is forecast to strengthen over the Gulf of
Mexico and could bring storm surge, rainfall, and wind impacts
to the northern U.S. Gulf Coast by the middle of next week.
Interests there should monitor the progress of Laura and updates to
the forecast during the next few days.

FORECAST POSITIONS AND MAX WINDS

INIT  22/1500Z 17.8N  66.8W   35 KT  40 MPH
 12H  23/0000Z 18.6N  69.4W   40 KT  45 MPH...INLAND
 24H  23/1200Z 19.4N  72.6W   40 KT  45 MPH...INLAND
 36H  24/0000Z 20.9N  76.3W   45 KT  50 MPH...INLAND
 48H  24/1200Z 22.4N  80.0W   45 KT  50 MPH...INLAND
 60H  25/0000Z 23.7N  83.2W   55 KT  65 MPH...OVER WATER
 72H  25/1200Z 25.2N  86.2W   65 KT  75 MPH
 96H  26/1200Z 27.9N  90.6W   75 KT  85 MPH
120H  27/1200Z 31.6N  92.5W   40 KT  45 MPH...INLAND

$$
Forecaster Pasch
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