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Tropical Storm Genevieve Discussion Number   3
NWS National Hurricane Center Miami FL       EP122020
1000 PM CDT Sun Aug 16 2020
 
Infrared (IR) and passive microwave (MW) satellite imagery indicate 
that Genevieve has continued to rapidly intensify while becoming 
better organized. A 17/0121Z SSMI/S MW image showed that the 
cyclone had already developed a 15-nmi-diameter, ragged mid-level 
eye, while both IR and MW data indicate tight banding features 
spiraling into a compact inner-core convective region. The initial 
intensity of 50 kt is based on unanimous T3.0/45 kt satellite 
classifications from TAFB and SAB, with the aforementioned eye 
feature nudging upward the final intensity assessment.

The initial motion estimate remains west-northwestward or 290/16 kt. 
The track forecast and reasoning remain unchanged and fairly 
straightforward. Genevieve is expected to move generally 
west-northwestward around the southwestern periphery of a sprawling 
deep-layer ridge located over the western United States and 
northern and central Mexico throughout the forecast period. The new 
NHC track forecast is very similar to the previous advisory track, 
and lies near the middle of the tightly packed consensus track model 
forecasts.

Now that Genevieve has developed a tight inner-core wind field and 
an eye feature, it isn't a question of will the cyclone rapidly 
strengthen, but rather how quickly and how much will the 
strengthening be! The deep-layer and mid-level vertical wind shear 
parameters are forecast to be weak at less than 5 kt through 72 
hours, while the upper-level outflow pattern is expected to steadily 
improve during that time, including the development of dual outflow 
channels to the north and south. These very favorable atmospheric 
conditions will coincide with a very moist mid-level regime and 
sea-surface temperatures (SST) of at least 30 deg C. As a result, 
the intensity forecast has been nudged upward, with rapid 
intensification (RI) of about 30 kt expected during next 24 h, 
followed by a slightly faster rate of RI in the 24-48 hour time 
frame when the dual outflow channels will be present. By 60-72 
hours, Genevieve is expected to be moving over shallower warm 
water, which should result in significant cold upwelling and the 
onset weakening. More rapid weakening is forecast thereafter due to 
the cyclone moving over 23-25 deg C SSTs. The official intensity is 
near the upper end of the guidance envelope, but remains below the 
ECMWF-based SHIPS model forecast which brings Genevieve to near 130 
kt in 48-60 hours.
 
Although the tropical cyclone is forecast to remain well offshore of
the southern coast of Mexico, large swells generated by the
strengthening system are expected to begin affecting portions of
the coast of southern Mexico over the next day or so.
 
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  17/0300Z 12.4N 100.4W   50 KT  60 MPH
 12H  17/1200Z 13.4N 102.7W   60 KT  70 MPH
 24H  18/0000Z 14.8N 105.7W   75 KT  85 MPH
 36H  18/1200Z 16.3N 108.2W   95 KT 110 MPH
 48H  19/0000Z 17.7N 110.1W  115 KT 130 MPH
 60H  19/1200Z 19.1N 111.5W  120 KT 140 MPH
 72H  20/0000Z 20.4N 112.9W  105 KT 120 MPH
 96H  21/0000Z 22.7N 116.0W   80 KT  90 MPH
120H  22/0000Z 24.7N 119.7W   55 KT  65 MPH
 
$$
Forecaster Stewart
 
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