[Tropical] Tropical Cyclone Discussion

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WTNT43 KNHC 241440
TCDAT3

Tropical Storm Laura Discussion Number  19
NWS National Hurricane Center Miami FL       AL132020
1100 AM EDT Mon Aug 24 2020

Laura's satellite presentation has degraded somewhat since
yesterday, however, there has been a recent increase in convection
near the center, and a large band over the southern periphery of
the circulation.  It appears that the combination of land
interaction, moderate northerly shear, and some dry air has
caused the change in structure. NOAA and Air Force reconnaissance
aircraft have reported several believable SFMR winds in the 45-50
kt range and a minimum pressure of around 1002 kt.  Based on these
observations, the initial wind speed has been set at 50 kt.

Laura is forecast to pass over the very warm water of the extreme
northwestern Caribbean Sea just south of the coast of Cuba today,
and some modest strengthening is possible before the center moves
over the western portion of Cuba this evening. Laura is then
forecast to emerge over the southeastern Gulf of Mexico overnight
where a combination of warm sea surface temperatures and a favorable
upper-level environment are expected to allow for steady
strengthening.  Given the very conducive upper-level wind pattern
depicted by the global models, a period of rapid strengthening is
possible once Laura re-organizes an inner core after its passage
over western Cuba.  The regional hurricane models remain quite
bullish on intensification, and the GFS and UKMET models indicate
significant deepening while Laura moves over the Gulf of Mexico. The
statistical guidance is not as aggressive, and the NHC forecast is
in good agreement with the intensity consensus aids which lie
between the higher solutions of the regional models and the SHIPS
and LGEM guidance.

Laura has been moving on a steady west-northwestward track over the
past day or so, and the initial motion estimate is 285/17 kt.  The
deep-layer ridge over the western Atlantic is forecast to build
westward over the eastern Gulf of Mexico during the next day or so,
and this should keep Laura on a west-northwestward heading through
Tuesday.  After that time, a mid- to upper-level trough over the
south-central United States should produce a break in the ridge over
the western Gulf of Mexico.  Laura should turn northwestward
Tuesday night in response to the break in the ridge, and the storm
is expected to reach the northwestern Gulf coast Wednesday night.
The cyclone should become embedded within the mid-latitude
westerlies by day 4, and Laura or its remnants should recurve to
the northeast and east-northeast by the end of the period.
Although the track guidance is in somewhat better agreement today,
there remains some cross-track spread by day 3, with the UKMET
showing landfall well southwest of the official forecast.  The NHC
track is close to the various consensus aids and leans toward the
typically reliable GFS and ECMWF models.

Users are again reminded to not to focus on the exact details of
the track or intensity forecasts as the average NHC track error at
72 h is around 100 miles and the average intensity error is around
15 mph (13 kt).  In addition, wind, storm surge, and rainfall
hazards will extend far from the center.

Key Messages:

1. Tropical storm conditions are expected across much of Cuba
today. Heavy rainfall is likely across Cuba and Jamaica today, and
these rains could cause mudslides and life-threatening flash and
urban flooding.  Tropical storm conditions are expected in the Dry
Tortugas, and the Middle and Lower Florida Keys later today.

2. There is an increasing risk of dangerous storm surge, wind, and
rainfall impacts from the upper Texas coast through the north-
central Gulf Coast beginning on Wednesday.  Interests in these
areas should monitor the progress of Laura and ensure they have
their hurricane plan in place, as storm surge and hurricane watches
will likely be issued later today.

FORECAST POSITIONS AND MAX WINDS

INIT  24/1500Z 21.2N  80.6W   50 KT  60 MPH
 12H  25/0000Z 22.2N  82.9W   55 KT  65 MPH
 24H  25/1200Z 23.6N  86.0W   60 KT  70 MPH
 36H  26/0000Z 25.2N  88.8W   70 KT  80 MPH
 48H  26/1200Z 26.8N  91.1W   80 KT  90 MPH
 60H  27/0000Z 28.7N  92.8W   90 KT 105 MPH
 72H  27/1200Z 31.2N  93.3W   65 KT  75 MPH...INLAND
 96H  28/1200Z 36.0N  90.9W   30 KT  35 MPH...INLAND
120H  29/1200Z 37.5N  81.0W   25 KT  30 MPH...POST-TROP/REMNT LOW

$$
Forecaster Brown
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