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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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