[Tropical] Tropical Cyclone Discussion

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WTNT43 KNHC 222052
TCDAT3

Tropical Storm Laura Discussion Number  12
NWS National Hurricane Center Miami FL       AL132020
500 PM AST Sat Aug 22 2020

A couple of hours ago an observing site on the southeast coast of
Puerto Rico, Las Mareas, reported sustained winds of 52 kt.  These
winds were apparently associated with a mesocyclone embedded within
the larger-scale circulation and not representative of the intensity
of the tropical storm.  Scatterometer data and WSR-88D Doppler
velocities from San Juan support an intensity of 45 kt. Since the
center should be moving over land for the next 48 hours or so, no
additional intensification is anticipated until Monday night when
the center moves over the southeastern Gulf of Mexico.  Over warm
waters, with anticipated weak vertical shear, and anticyclonic flow
aloft, Laura will likely strengthen into a hurricane before it
reaches the northern Gulf of Mexico coast.  The NHC intensity
forecast is close to the multi-model consensus, but given the
possibility of a favorable upper-air environment over the Gulf,
this forecast could be conservative.  At this time it does not seem
likely that Marco, which is forecast to make landfall on the
north-central Gulf coast a day or two earlier than Laura, should
have much of an influence on the latter system.

Center locations from earlier scatterometer data, low-cloud motions,
and Dvorak fixes from both TAFB and SAB, give a motion of about
280/16 kt.  Laura should move west-northwestward along the southern
side of a mid-tropospheric anticyclone centered near the
southeastern U.S. coast through 72 hours.  Then, the cyclone is
expected to turn northwestward to northward on the western side of
the high.  The official track forecast is on the right side of the
track guidance suite.

Given the predicted track and wind radii, a Tropical Storm Watch
has been issued for the Florida Keys and the Dry Tortugas.

Key Messages:

1. Tropical storm conditions are expected to continue across
portions of the U.S. Virgin Islands and Puerto Rico through this
evening. Tropical storm conditions are also expected across portions
of the Dominican Republic and Haiti, the Turks and Caicos, the
southeastern Bahamas, and central and eastern Cuba through 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 and Andros Island Sunday night and Monday, and in
the Florida Keys on Monday.

3. The details of the long-range track and intensity forecasts
remain uncertain 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 portions of the U.S. Gulf
Coast by the middle of next week. This could result in a prolonged
period of hazardous weather for areas that are likely to be
affected by Tropical Storm Marco earlier in the week. Interests
there should monitor the progress of Laura and Marco and updates to
the forecast during the next few days.

FORECAST POSITIONS AND MAX WINDS

INIT  22/2100Z 18.0N  68.1W   45 KT  50 MPH
 12H  23/0600Z 18.9N  70.6W   45 KT  50 MPH...INLAND
 24H  23/1800Z 20.1N  74.3W   45 KT  50 MPH...INLAND
 36H  24/0600Z 21.6N  78.1W   45 KT  50 MPH...INLAND
 48H  24/1800Z 23.0N  81.6W   45 KT  50 MPH...INLAND
 60H  25/0600Z 24.3N  84.5W   55 KT  65 MPH...OVER WATER
 72H  25/1800Z 25.7N  87.3W   65 KT  75 MPH
 96H  26/1800Z 29.0N  90.7W   75 KT  85 MPH
120H  27/1800Z 33.0N  91.0W   30 KT  35 MPH...INLAND

$$
Forecaster Pasch
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