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Hurricane Genevieve Discussion Number   8
NWS National Hurricane Center Miami FL       EP122020
300 AM MDT Tue Aug 18 2020
 
Genevieve continues to rapidly intensify this morning.  A recent
GMI microwave overpass shows a well-defined eye and eyewall
present, and the eye is becoming much better defined in conventional
infrared imagery.  Various objective and subjective satellite
intensity estimates were averaging about 90 kt at 06Z, and recent 
objective raw T-numbers from the CIMSS ADT technique have increased 
to between 100-115 kt.  Based on these data, the initial intensity 
is raised to 100 kt, making Genevieve a major category 3 hurricane 
on the Saffir-Simpson Hurricane Wind Scale.
 
The initial motion is now northwestward or 310/15 kt.  The
hurricane is on the southwest side of a deep-layer ridge, and the
global models forecast this feature to persist for the next several
days.  This should cause Genevieve to continue a northwestward
motion during the forecast period with some decrease in forward
speed.  On the forecast track, the center of the hurricane should
move parallel to, but offshore of, the southwestern coast of Mexico
and the Baja California peninsula.  The track model guidance
remains tightly clustered, and the new forecast track is a little
to the east of, and slightly slower than, the previous forecast.
 
Environmental conditions appear favorable for continued rapid
intensification during the next 24 h or so, with the only alternate
possibility being that the intensification is interrupted by an
eyewall replacement cycle.  By 36-48 h, the center will be over
decreasing sea surface temperatures and oceanic heat content, and
during that time, Genevieve should start weakening.  By the end of
the forecast period, the cyclone is forecast to be over sea surface
temperatures of 21-22C, which should cause rapid weakening.  The
new intensity forecast goes above the guidance in calling for a
peak intensity of 125 kt in 24 h, and it would not be a surprise if
Genevieve became stronger than that.  After the peak, the new
forecast shows steady to rapid weakening, and by 120 hours the
system is expected to degenerate into a convection-free
post-tropical cyclone.
 
The forecast track and wind radii require a Tropical Storm
Warning for the southern portion of the Baja California Peninsula
at this time.
 
Key Messages:
 
1. There is an increasing risk of tropical-storm-force winds over
the southern portion of the Baja California peninsula beginning
Wednesday afternoon and continuing into Thursday as Genevieve passes
near or southwest of the southern tip of Baja California, and a
Tropical Storm Warning is now in effect for a portion of this area.
 
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  18/0900Z 17.4N 107.1W  100 KT 115 MPH
 12H  18/1800Z 18.5N 108.7W  115 KT 130 MPH
 24H  19/0600Z 19.7N 110.0W  125 KT 145 MPH
 36H  19/1800Z 20.9N 111.0W  120 KT 140 MPH
 48H  20/0600Z 21.9N 111.9W  110 KT 125 MPH
 60H  20/1800Z 23.0N 113.0W   95 KT 110 MPH
 72H  21/0600Z 23.9N 114.4W   80 KT  90 MPH
 96H  22/0600Z 26.0N 117.5W   55 KT  65 MPH
120H  23/0600Z 28.5N 121.0W   35 KT  40 MPH...POST-TROPICAL
 
$$
Forecaster Beven
 
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