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Hurricane Genevieve Discussion Number   9
NWS National Hurricane Center Miami FL       EP122020
900 AM MDT Tue Aug 18 2020
 
Since the issuance of the last advisory, Genevieve has continued to
rapidly intensify. The major hurricane has a very well-defined and
clear eye and microwave imagery as recent as 12Z did not show any
indication of a secondary eyewall. Objective intensity estimates
from the UW-CIMSS SATCON were as high as 124 kt earlier this
morning, but subjective Dvorak estimates at 12Z were a little lower
due to the formation of a small break in the cold cloud tops
surrounding Genevieve's eye. Even then, a blend of all available
intensity estimates still supports an intensity of 115 kt for this
advisory.
 
Additional rapid strengthening is possible for at least the next
12 h given the current structure of the hurricane and the extremely
favorable environment it is moving through. The NHC forecast is well
above the guidance for the next 24 h out of respect for that
possibility. It is worth noting that eyewall replacement cycles are
generally poorly forecast and the onset of one could bring an
abrupt halt to Genevieve's intensification. By the time Genevieve
nears the Baja California peninsula on late Wednesday, rapid
weakening is expected as the system moves over cooler waters and
encounters an increase in southwesterly shear associated with an
upper-level trough to the northwest. Upwelling from the hurricane's
own wind field and decreasing forward speed could also bring about
weakening. By the end of the weak Genevieve will likely weaken to a
tropical storm and then become a remnant low.
 
The hurricane is moving slightly slower toward the northwest and a
further decrease in forward speed is anticipated for the next day
or two. There was no substantial change made to the NHC track
forecast, and Genevieve is still predicted to be steered just west
of the Baja California peninsula by a deep-layer ridge centered over
the southwestern U.S. The track guidance remains tightly clustered,
so confidence in the forecast remains fairly high.
 
Key Messages:
 
1. The center of Genevieve is forecast to move just west of the Baja
California peninsula, but it is still expected to cause tropical
storm conditions across portions of southern Baja California Sur.
These conditions are expected to begin Wednesday afternoon and
could spread northwestward through Thursday.
 
2. Large swells generated by Genevieve are affecting portions of the
coast of southern Mexico and will spread northward along the coast
of Mexico to the Baja California peninsula by Wednesday.
 
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  18/1500Z 18.0N 108.0W  115 KT 130 MPH
 12H  19/0000Z 19.0N 109.3W  130 KT 150 MPH
 24H  19/1200Z 20.2N 110.4W  130 KT 150 MPH
 36H  20/0000Z 21.3N 111.3W  120 KT 140 MPH
 48H  20/1200Z 22.2N 112.3W  105 KT 120 MPH
 60H  21/0000Z 23.2N 113.5W   90 KT 105 MPH
 72H  21/1200Z 24.1N 115.0W   75 KT  85 MPH
 96H  22/1200Z 26.3N 118.1W   50 KT  60 MPH
120H  23/1200Z 28.7N 121.4W   35 KT  40 MPH...POST-TROPICAL
 
$$
Forecaster Zelinsky
 
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