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Tropical Storm Hernan Discussion Number 7
NWS National Hurricane Center Miami FL EP132020
300 PM MDT Thu Aug 27 2020
Hernan has had a rather ragged appearance today with intermittent
convection firing around, but never really over the center. There
were no ASCAT overpasses during the day that directly sampled the
system's circulation. The latest Dvorak intensity estimates from
TAFB and SAB support 35 kt and 30 kt, respectively, while the
UW-CIMSS ADT and SATCON numbers range from 30 to 40 kt. Based on a
blend of these values, the initial intensity is being lowered to 35
kt.
Hernan should at least maintain its current strength through
tonight as it remains over very warm waters while battling moderate
easterly shear. This shear is not forecast to abate during the
forecast period. And by 24 h, the cyclone is expected to begin
moving over progressively cooler waters. The combination of these
two factors should induce a weakening trend. By 60 h, simulated
satellite imagery by global models suggest that the cyclone will
become devoid of deep convection. After that time, the remnant low
is expected to be absorbed within the broader circulation of
Iselle to its west. The latest NHC intensity forecast is in
agreement with the various intensity consensus aids.
Hernan is now moving northwest at about 5 kt. There is no change to
the track forecast reasoning. 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
is expected to continue to parallel the coast of southwestern Mexico
through this evening and should begin to increase its forward speed
tonight. A turn to the west-northwest then west is forecast Friday
through Friday night. The westward motion should continue until the
system becomes absorbed early next week.
FORECAST POSITIONS AND MAX WINDS
INIT 27/2100Z 19.6N 106.5W 35 KT 40 MPH
12H 28/0600Z 20.7N 107.6W 35 KT 40 MPH
24H 28/1800Z 21.6N 109.4W 30 KT 35 MPH
36H 29/0600Z 22.3N 111.1W 30 KT 35 MPH
48H 29/1800Z 22.5N 113.0W 25 KT 30 MPH
60H 30/0600Z 22.6N 114.8W 25 KT 30 MPH...POST-TROP/REMNT LOW
72H 30/1800Z...ABSORBED
$$
Forecaster Latto
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