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Tropical Storm Katia Discussion Number   3
NWS National Hurricane Center Miami FL       AL132017
400 AM CDT Wed Sep 06 2017

Conventional satellite imagery shows improved organization of the
cloud pattern during the past several hours, with recent cold cloud
top of -80C associated with deep convective bursts near the surface
center. An earlier SSMI/S microwave pass also revealed a developing
curved band feature in the eastern portion of the cyclone.
Additionally, a 0306 UTC ASCAT-B overpass indicated winds of 35 kt
in the aforementioned rain band.  A Dvorak satellite intensity
estimate of 35 kt from TAFB and the scatterometer wind data support
upgrading the depression to Tropical Storm Katia at this time.
The SHIPS model and the CIMSS shear analysis indicate westerly shear
impinging the western side of Katia, but the flow aloft appears to
be more diffluent now, indicative of the recent deep convective
outbreak.  Guidance continues to suggest that the shear will relax
in about 36 hours which should allow Katia to strengthen, possibly
to a hurricane as indicated in the HWRF forecast.  There are no
changes to the intensity forecast from the previous advisory, and
it's based on the IVCN multi-model.

The initial motion is estimated to be east-southeastward, or 110/2
kt. Katia has been drifting generally in this direction during the
past several hours within weak steering currents associated with a
mid-tropospheric trough digging southwestward from the Mississippi
Valley.  Later today, Katia should begin a gradual turn
southeastward and southwestward around the 36 hour period as a
mid-level ridge builds over the western gulf from Texas.  The
official forecast basically splits the guidance envelope and is
hedged toward the HFIP Corrected Consensus Model.


FORECAST POSITIONS AND MAX WINDS

INIT  06/0900Z 22.1N  96.3W   35 KT  40 MPH
 12H  06/1800Z 21.9N  96.0W   40 KT  45 MPH
 24H  07/0600Z 21.6N  95.6W   50 KT  60 MPH
 36H  07/1800Z 21.3N  95.4W   55 KT  65 MPH
 48H  08/0600Z 21.1N  95.6W   60 KT  70 MPH
 72H  09/0600Z 20.4N  96.7W   60 KT  70 MPH
 96H  10/0600Z 19.2N  98.7W   25 KT  30 MPH...POST-TROP/INLAND
120H  11/0600Z...DISSIPATED

$$
Forecaster Roberts

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