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Hurricane Grace Discussion Number  30
NWS National Hurricane Center Miami FL       AL072021
400 PM CDT Fri Aug 20 2021
 
The satellite presentation of Grace has greatly improved over the 
past several hours. Deep convection has become more concentrated 
over the center, and the central dense overcast now appears more 
symmetric. Dropsonde winds and peak 850-mb flight level wind  
measured by the Air Force Hurricane Hunters around midday were 
consistent with an intensity of around 75 kt. However, the surface 
pressure has been gradually falling throughout the day, and recent 
satellite data suggest the hurricane is becoming better organized. 
Therefore, the initial intensity is raised to 80 kt for this 
advisory, which is supported by the latest UW-CIMSS objective ADT 
estimate.

Given the high oceanic heat content within the southwestern Gulf of 
Mexico, additional strengthening is expected through Grace's 
landfall tonight. The 10-15 kt of northerly vertical wind shear over 
Grace does not appear to be having much of a negative effect on the 
cyclone at this time. Thus, the official NHC intensity forecast 
remains on the high end of the guidance envelope, and is closest to 
the statistical-dynamical models DSHP and LGEM. The current forecast 
shows Grace making landfall within the next 12-18 h. Once the center 
of Grace moves inland over the mountains of central Mexico, the 
cyclone should rapidly weaken and then dissipate by 48 h. However, 
its remnants appear likely to move into the eastern Pacific and lead 
to the development of a new tropical cyclone in that basin later 
this weekend or early next week.
 
Earlier reconnaissance data indicate that Grace has slowed down a 
bit today, and its initial motion is estimated to be 265/9 kt. This 
general motion should continue through landfall as Grace is steered 
by a mid-level ridge over the northern Gulf of Mexico. The official 
NHC track forecast is slightly slower, but otherwise very similar to 
the previous one and lies near the center of the guidance envelope.
 
Key Messages:
 
1. Hurricane conditions and dangerous storm surge are likely along 
portions of the coast of eastern mainland Mexico beginning this 
evening within the Hurricane Warning area 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 significant flash and urban flooding, along with the 
likelihood of mudslides. 
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  20/2100Z 20.5N  95.1W   80 KT  90 MPH
 12H  21/0600Z 20.4N  96.6W   90 KT 105 MPH...NEAR THE COAST
 24H  21/1800Z 19.9N  98.9W   45 KT  50 MPH...INLAND
 36H  22/0600Z 19.5N 101.9W   30 KT  35 MPH...INLAND
 48H  22/1800Z...DISSIPATED
 
$$
Forecaster Reinhart/Cangialosi
 
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