[Tropical] Tropical Cyclone Discussion

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WTNT43 KNHC 232055
TCDAT3

Tropical Storm Laura Discussion Number  16
NWS National Hurricane Center Miami FL       AL132020
500 PM EDT Sun Aug 23 2020

Satellite imagery and radar data from eastern Cuba show that the
center of Laura has been moving over water between Haiti and eastern
Cuba this afternoon.  There has been a recent uptick in convection
near the center and the radar imagery has shown an increase in
banding. An Air Force reconnaissance aircraft investigating Laura
this afternoon has reported a minimum pressure that has fallen to
around 1000 mb, and winds to support an intensity of 50 kt.  The
plane very recently found a small area of stronger flight-level
winds, but these winds may be associated with mesocyclone, and not
representative of the large scale circulation.

Laura continues to move briskly west-northwestward or 285/18 kt. The
track forecast reasoning remains the same as the previous advisory.
Laura should continue to move west-northwestward to the south of a
deep-layer ridge that is forecast to build westward across Florida
and the eastern Gulf of Mexico during the next day or two. The track
guidance has continued to edge southward for the portion of the
forecast near Cuba, and the NHC forecast has again been moved in
that direction.  Laura should continue moving west-northwestward
over the southeastern Gulf on Tuesday, but a turn toward the
northwest is expected Tuesday night as the cyclone nears the western
portion of the ridge.  A northwestward to north-northwestward motion
should then continue around the western portion of the ridge until
the cyclone reaches the northwestern Gulf coast.  The latest run of
the ECMWF has shifted significantly eastward, however its ensemble
mean and many of the stronger ensemble members remain farther west
as a stronger cyclone is likely to be steered more westward by the
deep-layer ridge. The GFS, UKMET, and HWRF remain close to the
previous NHC track, so little change was made to the official
forecast was made after 48 hours.

The intensity forecast during the next 24 hours is highly dependent
on the track and the amount of interaction Laura has with Cuba.  If
the storm stays along the southern coast or just offshore, the
environment of warm water and low vertical wind shear could allow
for some slight strengthening, but little overall change in
intensity is indicated during the next 24 hours. After the center
clears western Cuba, the upper-level wind pattern is predicted to
quite favorable while the storm traverses the warm waters of the
Gulf of Mexico.  The GFS, UKMET, and regional hurricane models all
indicate significant deepening, and the NHC intensity forecast has
been adjusted slightly upward. Although not explicitly shown, Laura
could threaten the northwestern Gulf coast near major hurricane
strength.

Users are again reminded to not to focus on the exact details of
the track or intensity forecast at the longer range as winds, storm
surge, and rainfall hazards will extend far from the center.

Key Messages:

1. Tropical storm conditions are expected across portions of the
Haiti, the southeastern Bahamas, and Cuba through Monday. Heavy
rainfall is likely across Haiti, Cuba, and Jamaica through Monday
and these rains could cause mudslides and life-threatening flash and
urban flooding.

2. Tropical storm conditions are possible over the Middle and Lower
Florida Keys and the Dry Tortugas on Monday.

3. While the details of the long-range track and intensity forecasts
remain uncertain, Laura is forecast to strengthen over the Gulf of
Mexico and there is an increasing risk of dangerous storm surge,
wind, and rainfall impacts along portions of the U.S. Gulf Coast by
the middle of the week. This could result in a prolonged period of
hazardous weather for areas that are likely to be affected by Marco.
Interests along the Gulf Coast should monitor the progress of Laura
and Marco and updates to the forecast during the next few days.

FORECAST POSITIONS AND MAX WINDS

INIT  23/2100Z 19.5N  75.2W   50 KT  60 MPH
 12H  24/0600Z 20.6N  78.3W   50 KT  60 MPH...NEAR CUBA
 24H  24/1800Z 21.8N  81.7W   50 KT  60 MPH...NEAR CUBA
 36H  25/0600Z 23.3N  84.9W   55 KT  65 MPH...OVER WATER
 48H  25/1800Z 24.7N  87.7W   60 KT  70 MPH
 60H  26/0600Z 26.1N  90.2W   75 KT  85 MPH
 72H  26/1800Z 28.0N  92.5W   90 KT 105 MPH
 96H  27/1800Z 32.7N  93.5W   45 KT  50 MPH...INLAND
120H  28/1800Z 37.0N  88.0W   25 KT  30 MPH...POST-TROPICAL

$$
Forecaster Brown
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