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Tropical Depression Seventeen-E Discussion Number   4
NWS National Hurricane Center Miami FL       EP172020
900 AM MDT Mon Sep 21 2020

Although the circulation still appears to be elongated, the 
depression has become a little better organized during the past 
several hours, with the low-level center closer to the large mass 
of convection in the southwestern semicircle.  Satellite intensity 
estimates from TAFB and SAB are 30 kt, so the initial intensity is 
nudged upward to 30 kt.

The initial motion is now 290/12.  The depression is being steered 
by a large low- to mid-level ridge to the north and northwest, and 
this ridge is forecast to persist through the forecast period.  The 
track guidance shows that the system should continue west- 
northwestward for about 36 h, followed by a westward motion through 
120 h.  The track guidance is very tightly clustered, and the new 
forecast track is near the various consensus models.

Current indications are that the current easterly shear should 
subside a little during the next 24-36 h, and this should allow the 
system to become a tropical storm.  As noted in the previous 
advisory, the intensity after 36 h will be strongly dependent on 
where the center is in relation to the strong sea surface 
temperature gradient.  The new intensity forecast is similar to the 
previous forecast based on the forecast track keeping the 
system over 25-26C water temperatures through 120 h.  However, any 
motion north of the forecast track would bring the center over 
colder water and lead to a system weaker than forecast, while any 
motion south of the track would keep it over warmer water and 
possibly allow the cyclone to become a hurricane.  As might have 
guessed, this is a low confidence intensity forecast.
 
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  21/1500Z 17.0N 112.0W   30 KT  35 MPH
 12H  22/0000Z 17.8N 113.7W   35 KT  40 MPH
 24H  22/1200Z 18.8N 115.9W   40 KT  45 MPH
 36H  23/0000Z 19.5N 118.0W   45 KT  50 MPH
 48H  23/1200Z 20.0N 119.9W   50 KT  60 MPH
 60H  24/0000Z 20.3N 121.7W   55 KT  65 MPH
 72H  24/1200Z 20.5N 123.4W   60 KT  70 MPH
 96H  25/1200Z 20.5N 126.5W   60 KT  70 MPH
120H  26/1200Z 20.5N 130.5W   50 KT  60 MPH
 
$$
Forecaster Beven
 
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