Tropical Storm Theta Forecast Discussion

WTNT45 KNHC 120849

Tropical Storm Theta Discussion Number  10
NWS National Hurricane Center Miami FL       AL302020
900 AM GMT Thu Nov 12 2020

Theta currently is comprised of a large swirl of low- to mid-level 
clouds with no convection near the center.  However, a band of 
convection is wrapped about three-quarters of the way around the 
center at a distance of about 200 n mi in the eastern semicircle 
and 100 n mi in the western semicircle.  Overall, the cyclone has 
somewhat of a subtropical appearance at this time.  Since there 
has been no data from the cyclone's core region since the last 
scatterometer pass, the initial intensity is held at 55 kt.  

The storm continued to jog a little to the left since the last 
advisory, but the last few satellite images suggest a more eastward 
motion has resumed.  The initial motion is a somewhat uncertain 
060/10.  For the next 24 h or so, Theta is expected to continue to 
move east-northeastward as it rounds the north side of a mid-level 
ridge centered over the Cabo Verde islands.  An eastward to 
east-southeastward motion is expected from 24-72 h as the mid-level 
ridge to the south weakens and mid- to upper-level northerly flow 
moves over the cyclone.  After that time, Theta or its remnants is 
expected to be steered northeastward in the low-level flow to the 
southeast of a deep-layer mid-latitude cyclone over the 
northeastern Atlantic.  The new forecast track is adjusted north of 
the previous track based on the initial position and motion, and it 
lies near the various consensus models.

Theta is forecast to change little in intensity during the next 36 
h or so as it moves into the light shear area near an upper-level 
trough axis.  After that time, the trough moves south of the 
cyclone, and strong northerly vertical shear should occur along 
with the entrainment of stable air.  This combination should cause 
Theta to quickly weaken, and the intensity forecast calls for the 
system to decay to a remnant low pressure area by 96 h.  The new 
intensity forecast has only minor adjustments from the old 
forecast, and it lies a little above the intensity consensus.


INIT  12/0900Z 31.7N  30.2W   55 KT  65 MPH
 12H  12/1800Z 32.0N  28.5W   55 KT  65 MPH
 24H  13/0600Z 32.3N  26.2W   55 KT  65 MPH
 36H  13/1800Z 32.3N  24.0W   55 KT  65 MPH
 48H  14/0600Z 32.0N  22.1W   50 KT  60 MPH
 60H  14/1800Z 31.7N  20.8W   40 KT  45 MPH
 72H  15/0600Z 31.6N  20.1W   35 KT  40 MPH
 96H  16/0600Z 33.0N  19.5W   30 KT  35 MPH...POST-TROP/REMNT LOW
120H  17/0600Z 37.0N  18.0W   30 KT  35 MPH...POST-TROP/REMNT LOW

Forecaster Beven


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