[Tropical] Tropical Cyclone Discussion

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WTNT43 KNHC 220238
TCDAT3

TROPICAL STORM LISA DISCUSSION NUMBER  10
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL132016
1100 PM AST WED SEP 21 2016

Lisa remains a sheared tropical cyclone.  Deep convection has
expanded in coverage this evening, but recent microwave imagery and
ASCAT data indicate that the low-level center is located near
the far western edge of the sharp gradient of cold cloud tops.  The
ASCAT pass did not cover much of the northeastern portion of the
circulation, but it did detected a large area of 35 kt winds to the
north and north-northeast of the center.  Based on these data and
satellite estimates of 35 and 45 kt, from SAB and TAFB respectively,
the initial intensity remains 40 kt.  Lisa is already located
within an area of strong upper-level southwesterly winds to the
southeast of a large upper-level low.  During the next day or two
the tropical storm is forecast to approach the cut-off low, which
according to the SHIPS model will produce 30-40 kt of shear over
Lisa.  As a result, the tropical cyclone is expected to weaken
and become a remnant low in about 3 days, and it could dissipate
before the end of the foreast period.  The new NHC intensity
forecast essentially an update of the previous forecast and is in
best agreement with the SHIPS and LGEM guidance.

The microwave and ASCAT fixes suggest that Lisa is moving
north-northwestward at about 6 kt, which is a little right of the
previous forecasts.  The cyclone is expected to move northwestward
toward a weakness in the subtropical ridge currently between 30
and 40W.  Later in the period, an amplifying mid- to upper-level
trough over the western Atlantic should cause Lisa or its remnants
to turn northward and recurve into the mid-latitude westerlies by
day 5.  The track guidance is in fairly good agreement, and only
a small eastward adjustment was required during the first 72 hours.
The updated track prediction is very close to the latest multi-model
consensus.

FORECAST POSITIONS AND MAX WINDS

INIT  22/0300Z 19.2N  32.8W   40 KT  45 MPH
 12H  22/1200Z 20.2N  33.8W   40 KT  45 MPH
 24H  23/0000Z 21.6N  35.2W   35 KT  40 MPH
 36H  23/1200Z 23.0N  36.5W   30 KT  35 MPH
 48H  24/0000Z 24.3N  37.8W   30 KT  35 MPH
 72H  25/0000Z 26.7N  40.5W   25 KT  30 MPH...POST-TROP/REMNT LOW
 96H  26/0000Z 31.0N  41.0W   25 KT  30 MPH...POST-TROP/REMNT LOW
120H  27/0000Z 36.5N  37.5W   25 KT  30 MPH...POST-TROP/REMNT LOW

$$
Forecaster Brown

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