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Hurricane Grace Discussion Number  31
NWS National Hurricane Center Miami FL       AL072021
1000 PM CDT Fri Aug 20 2021
 
Hurricane Grace has rapidly intensified this evening. Deep cold 
convection has been wrapping around the center, with some evidence 
of mesovorticies rotating within the eyewall following the GOES-16 
GLM lightning data. The Air Force Reserve Hurricane Hunters arrived 
in Grace around 0000 UTC and found that the storm had intensified 
into Category 2 hurricane with the pressure dropping down to 
967 mb, which is a pronounced deepening rate of 2 mb per hour 
compared to the previous advisory. More recently, the aircraft was 
able to pass through the northeastern eyewall, and recently found 
flight level winds up to 115 kt with SFMR winds of 105 kt. These 
observations support Grace being upgraded to a major hurricane this 
advisory, with maximum sustained winds of 105 kt.
 
Some additional strengthening is possible while Grace remains over 
the very warm waters in the Bay of Campeche, though the hurricane 
should be making landfall tonight within the next 3-6 hours just 
south of Tuxpan, Mexico. By tomorrow morning, the storm should be 
well inland, and rapid weakening will likely be underway over the 
very mountainous terrain of mainland Mexico. The latest NHC 
intensity forecast now had Grace dissipating over Mexico in about
36 hours. However, as discussed in previous advisories, while the 
low-level circulation is expected to dissipate, the mid-level vortex 
is forecast to survive the passage of Mexico, and this feature is 
likely to lead to the development of a new tropical cyclone in the 
eastern Pacific basin later this weekend or early next week.
 
Center fixes from the aircraft indicate that Grace has stayed on a 
mostly due westward heading, at 270/9 kt. This general motion, 
though with a bit more southward component should continue through 
landfall and dissipation. This southward deflection over often 
occurs with strong hurricanes in this region, due to the 
topographical effects of the wind field to the north ascending over 
the higher terrain.  The official NHC track is very similar to the 
previous advisory, and remains near the middle of the guidance 
consensus.
 
Key Messages:
 
1. Hurricane conditions and dangerous storm surge are likely along
portions of the coast of eastern mainland Mexico beginning tonight
and tomorrow morning within the Hurricane Warning area from Puerto
Veracruz northward to Cabo Rojo.

2.  A dangerous storm surge is likely near and to the north of the 
where the center of Grace crosses the coast of Mexico. 
 
3. Through the weekend, heavy rainfall across Veracruz, Puebla,
Tlaxcala, Hidalgo, northern Queretaro, and eastern San Luis Potosi
will lead to significant flash and urban flooding, along with the
likelihood of mudslides.
 
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  21/0300Z 20.7N  96.3W  105 KT 120 MPH
 12H  21/1200Z 20.3N  97.9W   75 KT  85 MPH...INLAND
 24H  22/0000Z 20.0N 100.9W   45 KT  50 MPH...INLAND
 36H  22/1200Z...DISSIPATED
 
$$
Forecaster Papin/Beven
 
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