[Tropical] Tropical Cyclone Discussion

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WTNT42 KNHC 201448
TCDAT2

Hurricane Grace Discussion Number  29
NWS National Hurricane Center Miami FL       AL072021
1000 AM CDT Fri Aug 20 2021

Grace is a strengthening tropical cyclone. Its structure has
continued to improve in satellite imagery this morning, with more
pronounced curved banding in its northern and eastern semicircles
and good upper-level outflow. An Air Force Reserve Hurricane Hunter
aircraft measured a peak 850-mb flight-level wind of 92 kt and peak
SFMR winds of 74 kt during a pass through the northeast quadrant
earlier this morning. These data support increasing the initial
intensity of 75 kt, which makes Grace a hurricane once again.
Dropsonde data from the aircraft indicate the minimum pressure has
fallen to 982 mb.

The warm waters of the Bay of Campeche are expected to support
additional intensification through landfall in mainland Mexico later
this evening or tonight, despite some light to moderate northerly
wind shear. Since the reconnaissance data revealed Grace is
strengthening quicker than previously forecast, the official NHC
intensity forecast was increased in the short-term. Grace is now
forecast to become a 90-kt hurricane in 12 h, which lies on the high
end of the intensity guidance. The center of Grace will be well
inland by 24 h, and rapid weakening is forecast thereafter as the
cyclone moves over the mountains of central Mexico. Although Grace
is forecast to dissipate by 48 h, its remnants will likely move into
the eastern Pacific and lead to the development of a new tropical
cyclone later this weekend or early next week.

The cyclone is moving just south of due west, or 265/12 kt. Grace
should continue moving westward to west-southwestward through
landfall to the south of a mid-level ridge over the northern Gulf of
Mexico. The official NHC track forecast remains near the middle of
the guidance envelope and has been adjusted just a bit southward
based on the latest multi-model consensus aids.

Key Messages:

1. Hurricane conditions and dangerous storm surge are likely along
portions of eastern mainland Mexico beginning late today within the
Hurricane Warning area from Puerto Veracruz northward to Cabo Rojo.

2. Through the weekend, heavy rainfall across Veracruz, Puebla,
Tlaxcala, Hidalgo, northern Queretaro, and eastern San Luis Potosi
will lead to flash and urban flooding, along with the likelihood of
mudslides.

FORECAST POSITIONS AND MAX WINDS

INIT  20/1500Z 20.6N  94.3W   75 KT  85 MPH
 12H  21/0000Z 20.4N  95.9W   90 KT 105 MPH
 24H  21/1200Z 20.0N  98.2W   55 KT  65 MPH...INLAND
 36H  22/0000Z 19.4N 101.1W   35 KT  40 MPH...INLAND
 48H  22/1200Z...DISSIPATED

$$
Forecaster Reinhart/Cangialosi
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