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Tropical Storm Hernan Discussion Number   5
NWS National Hurricane Center Miami FL       EP132020
300 AM MDT Thu Aug 27 2020
 
Although Hernan is a sheared tropical cyclone, another strong burst 
of deep convection with cloud tops of -83C to -86C has developed 
near and south through west of the center. An 0401Z ASCAT-A 
scatterometer pass revealed several 38-40 kt surface wind vectors of 
south through southwest of the center, so the initial intensity has 
been increased to 40 kt, which is supported by a recent UW-CIMSS 
SATCON estimate of 40 kt.
 
The initial motion is estimate is 355/04 kt. Hernan is expected to 
remain caught within a large-scale, eastern North Pacific cyclonic 
gyre during the next few days, which will result in Hernan moving 
counter-clockwise around the eastern and northern periphery of the 
gyre. The cyclone will continue to move slowly northward this 
morning, followed by a turn toward the northwest by Thursday 
afternoon, with a west-northwestward motion expected on Friday. By 
Saturday, Hernan is forecast to degenerate into a remnant low 
pressure system, and possibly even dissipate and merge with Tropical 
Storm Iselle when the two systems are west-southwest of Baja 
California. The new NHC track is a very similar to the previous 
advisory track, and lies close to a blend of the simple track 
consensus models TVCE and GFEX, and the NOAA-HCCA 
corrected-consensus model.
 
Hernan will remain in a moderate-to-strong easterly vertical wind 
shear regime for the next three days, which is expected to prevent 
any significant strengthening from occurring despite the cyclone 
being over warm waters and within a moist mid-level environment. 
By 60 hours, Hernan is forecast to degenerate into a remnant low, 
and possibly merge with Tropical Storm Iselle in 72-96 hours. The 
official intensity forecast is similar to the IVCN intensity 
consensus model.

FORECAST POSITIONS AND MAX WINDS
 
INIT  27/0900Z 18.6N 106.0W   40 KT  45 MPH
 12H  27/1800Z 19.5N 106.2W   40 KT  45 MPH
 24H  28/0600Z 20.7N 107.3W   40 KT  45 MPH
 36H  28/1800Z 21.9N 108.8W   35 KT  40 MPH
 48H  29/0600Z 22.7N 110.8W   30 KT  35 MPH
 60H  29/1800Z 22.7N 112.9W   30 KT  35 MPH...POST-TROP/REMNT LOW
 72H  30/0600Z 22.4N 114.2W   25 KT  30 MPH...POST-TROP/REMNT LOW
 96H  31/0600Z...DISSIPATED
 
$$
Forecaster Stewart
 
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