[Tropical] Tropical Cyclone Discussion

[EMWIN Server]

WTNT45 KNHC 130838
TCDAT5

Tropical Storm Theta Discussion Number  14
NWS National Hurricane Center Miami FL       AL302020
900 AM GMT Fri Nov 13 2020

A fortuitous 0348 UTC AMSR2 microwave pass revealed that Theta's
surface center was a little to the north of the previous advisory
position.  The image also indicated that the coldest brightness
temperatures were located in the northeast quadrant which sort of
conflicts with the earlier scatterometer data showing the stronger
surface winds in the southeast quadrant.  More than likely though,
these winds are being produced by the pressure gradient of the
cyclone and a mid-level ridge to the southeast.  Since the cloud
pattern has changed little during the past several hours and the
subjective satellite intensity estimate from TAFB hasn't either,
the initial intensity is held at 50 kt for this advisory.

Theta is forecast to change little in intensity during the next 12
hours or so as the cyclone continues moving in a low shear zone
associated with a mid- to upper-level trough axis.  On Saturday,
the trough migrates south of Theta, while strong northerly shear
and a more stable air mass intrude from the northwest to north.  As
a result, Theta is expected to spin down and degenerate to a
remnant low on Sunday and dissipate by mid next week.

Theta has been moving eastward during the last 12 hours within the
mid-level troposphere steering current provided by a mid-level
ridge extending westward from west Africa to the eastern tropical
Atlantic.  The short term motion, however, already appears to be
the anticipated to the right of track motion, or toward the
east-southeast.  Regardless, this general motion along with a
reduction in forward speed is forecast during the next couple of
days as a more vertically shallow Theta is influenced by the
low-level flow.  By day 3, the remnants of Theta are expected to
turn rather sharply northward and continue in this general motion
in response to an approaching deep-layer mid-latitude cyclone from
the northeastern Atlantic.  The NHC forecast is similar to the
previous one through the 72 hour period, then adjusted to the right
to align more with the various consensus aids.


FORECAST POSITIONS AND MAX WINDS

INIT  13/0900Z 31.9N  24.9W   50 KT  60 MPH
 12H  13/1800Z 31.7N  23.3W   50 KT  60 MPH
 24H  14/0600Z 31.4N  21.3W   45 KT  50 MPH
 36H  14/1800Z 31.1N  19.7W   45 KT  50 MPH
 48H  15/0600Z 30.9N  18.5W   40 KT  45 MPH
 60H  15/1800Z 31.1N  18.1W   30 KT  35 MPH...POST-TROP/REMNT LOW
 72H  16/0600Z 32.1N  18.2W   30 KT  35 MPH...POST-TROP/REMNT LOW
 96H  17/0600Z 36.0N  17.1W   25 KT  30 MPH...POST-TROP/REMNT LOW
120H  18/0600Z...DISSIPATED

$$
Forecaster Roberts
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