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Tropical Depression Thirteen-E Discussion Number   1
NWS National Hurricane Center Miami FL       EP132020
300 AM MDT Wed Aug 26 2020
 
The broad area of low pressure that the NHC has been tracking the 
past few days has become better defined based on a 0356Z ASCAT-B 
scatterometer overpass. Although the system is slightly elongated 
northeast-to-southwest, the center is well defined and deep 
convection has persisted west of the center despite strong easterly 
vertical wind shear of 25-30 kt. Thus, the low has been upgraded to 
Tropical Depression 13-E. The initial intensity of 30 kt is based 
on scatterometer surface wind speeds of 30-32 kt, which are 
consistent with T2.0/30-kt satellite classifications from TAFB-SAB.

The initial motion estimate is slowly north-northeastward or 025/04 
kt. The depression is embedded within an east-to-west oriented 
cyclonic gyre with a high-amplitude mid-level ridge located over 
the southwestern U.S. and northern Mexico. These gyre will cause the 
cyclone to move slowly northward today and northwestward on 
Thursday, with the ridge acting as a poleward block and forcing to 
system to turn west-northwestward to westward on Friday and 
Saturday. On the forecast track, the cyclone is expected to 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 NHC official track forecast closely 
follows the simple consensus model TVCE, and lies a little to 
the left or west of the corrected-consensus model HCCA and the 
ECMWF model tracks.

Strong easterly shear is forecast to persist through the next 24 
hours, so little if any strengthening is expected during that time. 
In fact, convection is likely to erode a little during the day 
today, and then redevelop closer to the center tonight when the 
shear begins to abate somewhat. In the 36-60 hour period, the shear 
is forecast to weaken considerably from the northeast, allowing for 
some slight strengthening to occur. However, the intensity is not 
expected to increase to more than 35-40 kt, with the strongest 
winds and heaviest rains remaining offshore the southwestern coast 
of Mexico. For those reason, a tropical warning has not been issued 
for southwestern Mexico at this time. The official intensity 
forecast follows a blend of the HCCA, HWRF, and ECMWF models 
intensity forecasts.
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  26/0900Z 17.5N 106.7W   30 KT  35 MPH
 12H  26/1800Z 18.1N 106.3W   30 KT  35 MPH
 24H  27/0600Z 19.0N 106.3W   35 KT  40 MPH
 36H  27/1800Z 20.1N 107.0W   35 KT  40 MPH
 48H  28/0600Z 21.3N 108.1W   35 KT  40 MPH
 60H  28/1800Z 22.3N 109.4W   35 KT  40 MPH
 72H  29/0600Z 23.3N 111.3W   30 KT  35 MPH
 96H  30/0600Z 23.3N 114.1W   25 KT  30 MPH...POST-TROP/REMNT LOW
120H  31/0600Z 22.7N 115.5W   20 KT  25 MPH...POST-TROP/REMNT LOW
 
$$
Forecaster Stewart
 
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