Issued at 400 AM CDT Fri Aug 20 2021

000
WTNT42 KNHC 200852
TCDAT2

Tropical Storm Grace Discussion Number 28
NWS National Hurricane Center Miami FL

AL072021
400 AM CDT Fri Aug 20 2021

Deep convection has increased near the center of Grace overnight
with improved banding structure over the eastern portion of the
circulation. An Air Force Reserve Hurricane Hunter aircraft
measured a peak 850-mb flight-level wind of 72 kt and SFMR winds of
58 kt during the aircraft's final pass through the northern portion
of the storm prior to 06Z. Based on those observations, the
initial wind speed was increased to 60 kt on the 06Z intermediate
advisory, and it remains at that value for now. Grace is close
to re-gaining hurricane strength, and the next reconnaissance
mission should be in the storm around 1200 UTC this morning.

Grace will be moving over the warm waters over the Bay of
Campeche today. That, along with light to moderate vertical wind
shear conditions, are expected to allow for re-intensification
until landfall in mainland Mexico tonight. The updated intensity
forecast brings Grace to a 75-kt hurricane in 12 hours, and the
storm could be slightly stronger when it makes landfall overnight.

By 24 h, the center is forecast to be inland, and Grace will
likely already to have begun to weaken. Rapid weakening should
occur on Saturday as Grace moves farther inland over the
mountainous terrain of central Mexico, and the circulation is likely
to dissipate in around 48 hours. The remnants of Grace are expected
to move into the Pacific where they are likely to spawn a new
tropical cyclone.

The cyclone has been moving westward or 270/14 kt. A strong
mid-level ridge to the north of Grace should continue to steer the
cyclone westward to west-southwestward until dissipation occurs in
a couple days. The new NHC track forecast is near the middle of
the guidance envelope and is essentially unchanged from the
previous advisory.

Key Messages:

1. Hurricane conditions and dangerous storm surge are likely along
portions of eastern mainland Mexico beginning late today. A
Hurricane Warning is in effect 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 20/0900Z 20.7N 93.3W

60 KT 70 MPH
12H 20/1800Z 20.6N 95.2W

75 KT 85 MPH
24H 21/0600Z 20.3N 97.4W

70 KT 80 MPH...INLAND
36H 21/1800Z 19.8N 99.7W

35 KT 40 MPH...INLAND
48H 22/0600Z 19.4N 102.2W

20 KT 25 MPH...POST-TROP/REMNT LOW
60H 22/1800Z...DISSIPATED

$$
Forecaster Brown

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