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Tropical Storm Lowell Discussion Number   5
NWS National Hurricane Center Miami FL       EP172020
300 PM MDT Mon Sep 21 2020

Tropical Depression Seventeen-E has continued to have a ragged 
appearance in satellite imagery during the day.  The circulation is 
elongated, with the main center just northeast of a poorly organized 
convective mass and a secondary vorticity maximum well to the 
north-northeast near Socorro Island.  However, recent scatterometer 
data showed an area of 35-40 kt winds to the south and southeast of 
the main center.  Based on this, the depression is upgraded to 
Tropical Storm Lowell with an initial intensity of 40 kt.
 
The initial motion is now 290/14 kt.  There are no significant 
changes in the track forecast philosophy, the track forecast 
guidance, or the track forecast since the last advisory.  Lowell 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 still very tightly 
clustered, and the new forecast track is near the various consensus 
models.

Lowell is still experiencing some easterly shear, which the models 
suggest should abate some in the next 12 h or so.  However, the 
poor organization of the storm suggests it may take a while to 
respond to the more favorable environment.  Thus, the new intensity 
forecast continues the trend of the old forecast in showing slow 
strengthening for the first 36-48 h.  After that time, the intensity 
will be strongly dependent on where the center is in relation to the 
strong sea-surface temperature gradient.  Since the forecast track 
is basically unchanged, the new intensity forecast has only minor 
tweaks from 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.  The intensity 
forecast remains low confidence.
 
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  21/2100Z 17.4N 113.6W   40 KT  45 MPH
 12H  22/0600Z 18.3N 115.2W   45 KT  50 MPH
 24H  22/1800Z 19.2N 117.5W   50 KT  60 MPH
 36H  23/0600Z 19.8N 119.4W   55 KT  65 MPH
 48H  23/1800Z 20.2N 121.1W   60 KT  70 MPH
 60H  24/0600Z 20.5N 122.8W   60 KT  70 MPH
 72H  24/1800Z 20.5N 124.4W   60 KT  70 MPH
 96H  25/1800Z 20.5N 128.0W   60 KT  70 MPH
120H  26/1800Z 20.5N 131.5W   50 KT  60 MPH
 
$$
Forecaster Beven
 
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