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Tropical Storm Hernan Discussion Number   3
NWS National Hurricane Center Miami FL       EP132020
400 PM CDT Wed Aug 26 2020
 
Despite the rather poor presentation in satellite imagery, a recent 
ASCAT overpass showed that tropical-storm-force winds partially 
associated with a broader scale monsoon gyre are occurring over the 
southern portion of the circulation about 50-90 n mi from the 
center. Based on the wind data, the initial intensity has been 
raised to 35 kt, and the depression has been upgraded to Tropical 
Storm Hernan. 
 
Hernan is a sheared tropical cyclone, with only a small area of deep 
convection just to the south of the center. The SHIPS guidance 
indicates that this shear will continue throughout the forecast 
period. While the cyclone remains over very warm waters of about 29 
degrees C for the next 24-36 h, there should be sufficient 
convection to maintain Hernan's current intensity. However, after 36 
h the cyclone will move over relatively cooler waters of about 26 
C. These very marginal water temperatures combined with the ongoing 
shear should cause Hernan to weaken, and the system is expected to 
degenerate to a remnant low by 60 h, as indicated by the GFS 
simulated satellite. The NHC intensity is a blend of the various 
corrected consensus aids and the SHIPS intensity guidance.
 
Hernan appears to have made its anticipated turn to the northeast 
and the initial motion is 040/5 kt. The cyclone is expected to  turn 
north then northwest over the next 24 h as it pivots around inside a 
cyclonic gyre that includes Tropical Depression Fourteen-E to its 
west. After that time, Hernan should be steered west-northwestward 
to westward by a mid-tropospheric ridge anchored over the 
southwestern U.S.. On this forecast track, Hernan and most of its 
winds and convection should remain just offshore the southwestern 
coast of Mexico today and Thursday, and pass near or just south of 
the southern tip of Baja California Sur on Friday and Saturday. The 
official NHC forecast is little changed from the previous one, and 
is near the various consensus aids. 
 
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  26/2100Z 17.7N 105.8W   35 KT  40 MPH
 12H  27/0600Z 18.4N 105.7W   35 KT  40 MPH
 24H  27/1800Z 19.5N 106.1W   35 KT  40 MPH
 36H  28/0600Z 20.7N 107.3W   35 KT  40 MPH
 48H  28/1800Z 21.7N 108.9W   30 KT  35 MPH
 60H  29/0600Z 22.2N 110.7W   30 KT  35 MPH...POST-TROP/REMNT LOW
 72H  29/1800Z 22.5N 112.7W   25 KT  30 MPH...POST-TROP/REMNT LOW
 96H  30/1800Z 22.4N 115.1W   20 KT  25 MPH...POST-TROP/REMNT LOW
120H  31/1800Z...DISSIPATED
 
$$
Forecaster Latto
 
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