[Tropical] Tropical Cyclone Discussion

[EMWIN Server]

WTNT42 KNHC 181500
TCDAT2

Hurricane Grace Discussion Number  21
NWS National Hurricane Center Miami FL       AL072021
1100 AM EDT Wed Aug 18 2021

Grace is becoming better organized on satellite images with a
comma-shaped cloud pattern, and the upper-level outflow remains
well defined.  Wind gusts well into the hurricane-force range were
measured on Grand Cayman earlier this morning, along with some
damage on the island.  Recent flight-level and SFMR observations
from both the Air Force and NOAA Hurricane Hunter aircraft support
sustained 65-kt surface winds, so the system is being upgraded to a
hurricane on this advisory.

Although Grace is situated over waters of very high oceanic heat
content, moderate northwesterly shear and only marginally moist
mid-level air could slightly impede intensification.  However,
some additional strengthening is expected before landfall tonight
or early Thursday.  Weakening will occur due to Grace's passage
over Yucatan, although that land mass has relatively low terrain.
Reintensification is anticipated over the Bay of Campeche on
Friday, and the system should regain hurricane strength before
reaching the east coast of mainland Mexico.  The official intensity
forecast is similar to the numerical model consensus.

Grace has been moving west-northwestward near 13 kt.  A prominent
mid-tropospheric ridge is likely to remain in place to the north of
the cyclone for the next several days.  This pattern should keep
steering Grace on a west-northwestward to westward track for 72-96
hours.  The track guidance models are in excellent agreement and
little change has been made to the NHC track forecast compared to
the previous few packages.

A Hurricane Watch will likely be required for a portion of the
coast of eastern mainland Mexico later today.

Key Messages:

1. Hurricane conditions and a dangerous storm surge are expected
in portions of the Hurricane Warning area in the eastern Yucatan
Peninsula of Mexico beginning late tonight or early Thursday.
Preparations to protect life and property should be rushed to
completion.

2. There is an increasing risk of hurricane conditions and dangerous
storm surge in portions of eastern mainland Mexico beginning late
Friday, and a Hurricane Watch will likely be issued for part of this
area later today.

3. Over the next few days, heavy rainfall across the Cayman Islands
as well as portions of the Yucatan Peninsula and Veracruz State
should lead to flash and urban flooding, with mudslides possible in
the Mexican state of Veracruz.

FORECAST POSITIONS AND MAX WINDS

INIT  18/1500Z 19.4N  82.2W   65 KT  75 MPH
 12H  19/0000Z 19.7N  84.5W   70 KT  80 MPH
 24H  19/1200Z 20.3N  87.6W   75 KT  85 MPH...INLAND
 36H  20/0000Z 20.6N  90.5W   50 KT  60 MPH...OVER WATER
 48H  20/1200Z 20.7N  93.2W   65 KT  75 MPH...OVER WATER
 60H  21/0000Z 20.7N  95.3W   75 KT  85 MPH
 72H  21/1200Z 20.5N  97.7W   60 KT  70 MPH...INLAND
 96H  22/1200Z 20.0N 103.0W   20 KT  25 MPH...POST-TROP/INLAND
120H  23/1200Z...DISSIPATED

$$
Forecaster Pasch
This weather bulletin was brought to you by:
www.nashvilleweather.net