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Tropical Storm Hernan Discussion Number   4
NWS National Hurricane Center Miami FL       EP132020
1000 PM CDT Wed Aug 26 2020
 
Hernan remains a sheared tropical cyclone with a new burst of deep 
convection, characterized by cloud tops of -75C to -85C, having 
developed near and southwest of the well-defined low-level 
circulation center. The initial intensity remains 35 kt based on a 
TAFB Dvorak satellite classification of T2.5/35 kt using a shear 
pattern.

Up until a few hours ago, Hernan had been moving slowly 
north-northeastward, but the motion is now estimated to be northward 
or 360/05 kt. Hernan is forecast to remain trapped within and move 
around the northeastern periphery of a large-scale, eastern North 
Pacific monsoon gyre during the next few days. This is expected to 
result in a slow northward motion tonight, followed by a turn toward 
the northwest on Thursday, and a west-northwestward motion on 
Friday. By Saturday, Hernan is forecast to degenerate into a remnant 
low pressure system and be steered generally westward by the 
low-level easterly flow on the north side of the gyre. On the 
forecast track, Hernan and most of its significant winds and 
convection should remain just offshore the southwestern coast of 
Mexico tonight and Thursday, and pass near or just south of the 
southern tip of Baja California Sur on Friday and Saturday. The new 
NHC track is a very similar to the previous advisory track, and lies 
close to the simple track consensus models TVCE and GFEX, and lies 
to the left of the NOAA-HCCA corrected-consensus model.
 
Hernan is expected to remain a sheared tropical cyclone throughout 
its lifetime due to moderate to strong east to northeasterly 
vertical wind shear. However, the cyclone will also be over warm 
waters and within a moist mid-level environment for the next 48 
hours or so. Although the official intensity forecast calls for no 
change in strength, some slight intensification to 40 kt can't be 
ruled out, especially tonight during the approaching convective 
maximum period. By 60 hours and beyond, Hernan is forecast to move 
over marginal sea-surface temperatures and be affected by strong 
easterly shear of at least 20 kt, which should cause the cyclone to 
weaken into a remnant low. The NHC intensity forecast follows the 
IVCN intensity consensus model.
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  27/0300Z 18.3N 105.8W   35 KT  40 MPH
 12H  27/1200Z 19.0N 105.9W   35 KT  40 MPH
 24H  28/0000Z 20.2N 106.6W   35 KT  40 MPH
 36H  28/1200Z 21.4N 108.1W   35 KT  40 MPH
 48H  29/0000Z 22.0N 109.9W   30 KT  35 MPH
 60H  29/1200Z 22.5N 112.3W   30 KT  35 MPH...POST-TROP/REMNT LOW
 72H  30/0000Z 22.5N 113.8W   25 KT  30 MPH...POST-TROP/REMNT LOW
 96H  31/0000Z 22.4N 115.7W   20 KT  25 MPH...POST-TROP/REMNT LOW
120H  01/0000Z...DISSIPATED
 
$$
Forecaster Stewart
 
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