[Tropical] Tropical Cyclone Discussion

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WTNT43 KNHC 220906
TCDAT3

Tropical Storm Laura Discussion Number  10
NWS National Hurricane Center Miami FL       AL132020
500 AM AST Sat Aug 22 2020

Surface observations and Doppler radar data from Puerto Rico
indicate that the center of Laura is currently over the Virgin
Islands, eastern Puerto Rico, and the adjacent Caribbean waters.
Overall, the system has become a little better organized since the
last advisory, with strong convection forming not far from the
center to the east and southeast and a somewhat better defined
circulation.  However, the central area of light winds is quite
large, and there is evidence of several vorticity centers rotating
around the mean storm center.  Earlier scatterometer data
suggested that the maximum winds had decreased to 35 kt, and that is
the initial intensity for this advisory.

The initial motion is a somewhat uncertain 280/18.  There is no
change in the track forecast philosophy, as a subtropical ridge
over the central and western Atlantic is expected to expand
westward, causing Laura to move quickly west-northwestward for the
next 3 days or so.  After that, the storm should turn northwestward
toward the western edge of the ridge over the northern Gulf coast.
While the dynamical models are in good agreement with the general
scenario, there is an unusual amount of cross track spread.  The
track guidance is spread from the Florida Keys to the western end
of Cuba as the storm enters the Gulf of Mexico, and the models
have potential landfall locations along the Gulf coast from the
Florida Panhandle to the middle Texas coast.  One complicating
factor is the potential for interaction with Tropical Storm Marco,
although at this time the model guidance suggests the storms will
stay far enough apart to prevent direct interaction.  The new
forecast track is similar to the previous track through 72 hr, then
it is shifted a bit to the west after that time.  The new track
lies near the various consensus models.

Laura is moving into an environment of light shear, and combined
with the somewhat improved organization it suggests the storm
should strengthen.  However, the forecast track takes the center
over Hispaniola and then down the length of Cuba, which should at
least slow any intensification.  This is reflected in the new
intensity forecast which shows slow strengthening.  Over the Gulf of
Mexico, warm water and a likely favorable shear environment should
allow Laura to become a hurricane, a scenario now supported by much
of the guidance.

Key Messages:

1. Tropical storm conditions are expected across portions of the
northern Leeward Islands, the Virgin Islands, and Puerto Rico
through 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 beginning and could
cause mudslides and flash and urban flooding through Sunday.

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 could bring storm surge, rainfall, and wind impacts
to portions of Cuba, the Bahamas, and Florida early next week and
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  22/0900Z 17.6N  65.5W   35 KT  40 MPH
 12H  22/1800Z 18.2N  67.7W   40 KT  45 MPH
 24H  23/0600Z 19.1N  71.0W   40 KT  45 MPH...INLAND
 36H  23/1800Z 20.3N  74.6W   45 KT  50 MPH...INLAND
 48H  24/0600Z 21.6N  78.3W   45 KT  50 MPH...INLAND
 60H  24/1800Z 23.1N  81.8W   45 KT  50 MPH...INLAND
 72H  25/0600Z 24.6N  84.7W   55 KT  65 MPH...OVER WATER
 96H  26/0600Z 27.5N  89.5W   75 KT  85 MPH...OVER WATER
120H  27/0600Z 31.0N  92.0W   55 KT  65 MPH...OVER WATER

$$
Forecaster Beven
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