[Tropical] Tropical Cyclone Discussion

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WTNT42 KNHC 191444
TCDAT2

Tropical Storm Grace Discussion Number  25
NWS National Hurricane Center Miami FL       AL072021
1000 AM CDT Thu Aug 19 2021

Grace made landfall as a hurricane near Tulum, Mexico around 0945
UTC (445am CDT). A storm chaser in Tulum reported a minimum
pressure of 983 mb at the time of landfall. Since then, the cyclone
has moved further inland where observations are far more
sparse, and we have no recent in situ observations to assist the
intensity analysis. The intensity is therefore set at 55 kt, based
in part on the inland decay wind model built into the SHIPS model.
The central pressure estimate of 995 mb is likewise uncertain.

Some additional weakening is likely this afternoon while Grace
continues to cross the Yucatan peninsula. The tropical storm should
emerge over the southern Gulf of Mexico this evening, and
re-strengthening is anticipated shortly thereafter. Environmental
conditions are expected to be quite conducive for strengthening,
but it will likely take Grace at least a little time to redevelop
its inner-core after disruption by land. That could act to limit
the rate at which the cyclone will intensify at first. The HWRF and
HMON both suggest that the most significant reintensification could
occur in the last 12 hours before final landfall occurs in mainland
Mexico, and that scenario seems likely. It would not be surprising
if Grace strengthened slightly more between the 36 h forecast point
over water and the 48 h point inland, particularly if the hurricane
moves slightly slower, giving it more time over the warm waters of
the southern Gulf of Mexico. After landfall, Grace should quickly
weaken and dissipate over the mountainous terrain of Mexico.
Overall, the NHC intensify forecast is very similar to the previous
advisory.

Grace continues to move to the west near 16 kt. A westward or
west-northwestward motion is likely for the next 12 hours or so,
after which a strong-deep layer ridge extending well over the
northern Gulf of Mexico and southern U.S. will steer Grace westward
until landfall. Only minor adjustments were made to the official
track forecast, which remains near the multi-model consensus.
Although the tropical cyclone will quickly dissipate after it moves
inland, the ridge will likely steer its remnants further westward
toward the eastern North Pacific, where it could contribute to the
formation of a new tropical cyclone there.

Key Messages:

1. Tropical storm conditions will continue today across the
northern Yucatan Peninsula.

2. Hurricane conditions and dangerous storm surge is likely along
portions of eastern mainland Mexico beginning late Friday. A
Hurricane Warning is in effect from Puerto Veracruz northward to
Cabo Rojo.

3. Through the weekend, heavy rainfall across central and northern
portions of the Yucatan Peninsula and Veracruz State should lead to
flash and urban flooding. In addition, the heavy rainfall from Grace
will be capable of producing mudslides in Veracruz.


FORECAST POSITIONS AND MAX WINDS

INIT  19/1500Z 20.2N  88.8W   55 KT  65 MPH
 12H  20/0000Z 20.6N  91.2W   55 KT  65 MPH...OVER WATER
 24H  20/1200Z 20.6N  94.0W   65 KT  75 MPH
 36H  21/0000Z 20.4N  96.3W   75 KT  85 MPH
 48H  21/1200Z 20.0N  98.7W   40 KT  45 MPH...INLAND
 60H  22/0000Z 19.6N 101.7W   25 KT  30 MPH...POST-TROP/INLAND
 72H  22/1200Z...DISSIPATED

$$
Forecaster Zelinsky
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