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
