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Tropical Storm Genevieve Discussion Number   4
NWS National Hurricane Center Miami FL       EP122020
400 AM CDT Mon Aug 17 2020
 
Genevieve's infrared satellite presentation continues to improve in 
organization, with the center embedded beneath a Central Dense 
Overcast and strong convection occurring in two bands to the 
southwest and northwest of the center.  There has been a dearth of 
microwave data over the cyclone during the past few hours, so it's 
difficult to know how the internal structure has changed, but 
subjective and objective satellite estimates all support raising 
the intensity to 55 kt.

Genevieve's motion has not changed--still west-northwestward (290 
degrees) at 16 kt.  The cyclone will be moving along the periphery 
of a strong mid-level ridge which extends from the southwestern 
United States southeastward into Mexico.  This ridge should steer 
Genevieve toward the west-northwest or northwest for the entire 
5-day forecast period, but small variations in the strength and 
orientation of the ridge will play a role in how close Genevieve 
gets to the southern portion of the Baja California peninsula.  The 
track models are showing a slight bend to the storm's forecast path 
in 2-3 days, with the most recent run of the GFS showing a much 
closer approach to the Baja California peninsula.  At this stage, 
however, that model is a bit of an outlier compared to the other 
guidance.  Still, given the new set of models, the updated NHC 
track forecast has been shifted north and east of the previous 
track prediction, and it lies very close to the ECMWF, HWRF, and 
HCCA model solutions.

Some of the intensity guidance for Genevieve is incredible.  Due to 
low shear, very warm water, and high atmospheric moisture, several 
of the various SHIPS Rapid Intensification (RI) indices for the 
12-, 24-, and 36-hour forecast periods are between 95 and 100 
percent--numbers that suggest there is little doubt that Genevieve 
will go through a period of significant RI during the next couple 
of days.  RI is explicitly shown in the NHC intensity forecast, 
which is very near the HCCA and Florida State Superensemble 
solutions and shows Genevieve peaking as a category 4 hurricane in 
about 48 hours.  Amazingly, the LGEM and COAMPS-TC models are even 
higher than what is indicated in the official forecast, showing a 
peak intensity of 125-130 kt.  A combination of cooler waters and 
increasing shear (especially at the end of the forecast period) is 
expected to cause weakening on days 3 through 5.
 
Large swells generated by Genevieve are expected to begin affecting 
portions of the coast of southern Mexico today and will spread 
northward along the coast of Mexico to the Baja California 
peninsula by Wednesday.
 
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  17/0900Z 13.3N 101.7W   55 KT  65 MPH
 12H  17/1800Z 14.4N 104.0W   75 KT  85 MPH
 24H  18/0600Z 16.0N 106.7W   95 KT 110 MPH
 36H  18/1800Z 17.4N 108.7W  110 KT 125 MPH
 48H  19/0600Z 18.7N 110.1W  120 KT 140 MPH
 60H  19/1800Z 20.0N 111.2W  115 KT 130 MPH
 72H  20/0600Z 21.3N 112.3W  100 KT 115 MPH
 96H  21/0600Z 23.5N 115.0W   70 KT  80 MPH
120H  22/0600Z 25.5N 118.5W   45 KT  50 MPH
 
$$
Forecaster Berg
 
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