Issued at 1100 AM EDT Wed Aug 18 2021


000
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
 

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