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Hurricane Grace Discussion Number  24
NWS National Hurricane Center Miami FL       AL072021
400 AM CDT Thu Aug 19 2021
 
After a brief convective hiatus between 0400-0700 UTC, deep 
convection in the inner-core region has increased and become better 
organized during the past couple of hours. An Air Force Reserve 
Hurricane Hunter aircraft investigating Grace more than 4 hours ago 
reported a central pressure of 986 mb -- down 2 mb from previous 
passes -- and a maximum 700-mb flight-level wind speed of 74 kt on 
its last leg northbound around 0500 UTC. The 74-kt flight-level wind 
equates to about a 67-kt surface wind speed. These data supported 
maintaining a 70-kt intensity at 0600 UTC. The upper-level outflow 
remains symmetrical and has been expanding somewhat over the past 
few hours.

The initial motion is 280/15 kt based on the earlier recon fixes and 
passive microwave satellite data. Grace should continue to move 
generally westward for the next 48 hours, crossing the coast of the 
eastern Yucatan Peninsula within the next couple of hours, followed 
by a track across the Yucatan and emergence over the Bay of Campeche 
by 24 hours, with a subsequent landfall along the eastern coast of 
mainland Mexico shortly after the 48-hour forecast period. This 
track scenario is consistent with the latest 0000 UTC global and 
regional models, which show the strong deep-layer ridge to the north 
of Grace maintaining its expansive presence across the western 
Atlantic, Gulf of Mexico, and northern Mexico. After the second 
landfall, Grace is expected to turn west-southwestward and 
dissipate over the mountains of central Mexico by 72 hours. The new 
NHC forecast track is similar to the previous advisory track, and 
lies along the northern edge of the tightly packed consensus track 
models.
 
Given the recent improvement in Grace's inner-core convective 
structure noted in high-resolution infrared satellite imagery, some 
slight strengthening to 75 kt could still occur just prior to 
landfall this morning. Weakening will commence once Grace moves 
inland over Yucatan, with re-strengthening expected after the 
cyclone emerges over the Bay of Campeche where the vertical wind 
shear is forecast to decrease below 10 kt. Grace is expected to be a 
hurricane when the second landfall occurs along the coast of 
mainland Mexico, with the cyclone possibly reaching a peak 
intensity of 75 kt shortly after the 48-hour period. After final 
landfall in mainland Mexico, Grace should quickly weaken and 
dissipate over the mountains of Mexico by 72 hours, if not sooner.  
The remnants of Grace are expected to emerge over the eastern North 
Pacific and possibly re-develop there, but the uncertainty of 
whether this will be the original center or a new center precludes 
forecast points over the Pacific at this time.
 
A Hurricane Warning will likely be required for portions of the 
Hurricane Watch area of mainland Mexico later this morning or 
afternoon.
 
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 during the next several hours. 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 is in effect for part of this area.
 
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  19/0900Z 20.0N  87.2W   70 KT  80 MPH
 12H  19/1800Z 20.3N  89.7W   50 KT  60 MPH...INLAND
 24H  20/0600Z 20.6N  92.6W   60 KT  70 MPH...OVER WATER
 36H  20/1800Z 20.5N  95.0W   70 KT  80 MPH
 48H  21/0600Z 20.1N  97.3W   55 KT  65 MPH...INLAND
 60H  21/1800Z 19.7N 100.1W   20 KT  25 MPH...POST-TROP/INLAND
 72H  22/0600Z...DISSIPATED
 
$$
Forecaster Stewart
 
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