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Tropical Storm Marty Discussion Number 2
NWS National Hurricane Center Miami FL EP132021
900 AM MDT Mon Aug 23 2021
Marty is now a sheared tropical cyclone owing to northeasterly
vertical wind shear of about 15 kt, which has displaced the bulk of
the deep convection, with cloud tops colder than -80C, into the
western semicircle. The low-level center is estimated be located
near the northeastern edge of the sharp convective cloud shield. The
initial intensity remains 35 kt based on a subjective Dvorak
satellite intensity estimate of T2.5/35 kt from TAFB and an
objective estimate of T2.6/37 kt from UW-CIMSS ADT.
The initial motion remains westward or 280/13 kt. A strong
deep-layer subtropical ridge to the north of Marty is forecast by
the global and regional models to remain entrenched across the
eastern Pacific basin, keeping Marty moving in a general westward
direction for the next couple of days. On days 3 and 4, the ridge is
forecast build southward slightly, nudging the cyclone in a
west-southwestward direction. The new NHC track forecast is similar
to but slightly north, or right, of the previous advisory track, and
is also a little south of the tightly packed consensus track models
which have shifted northward on this cycle.
The moderate northeasterly shear currently affecting Marty is
forecast to gradually decrease to 10 kt or less and also become
easterly during the next 24-36 hours while the cyclone remains over
sea-surface temperatures (SST) of 26 deg C or greater. These
favorable conditions should allow for at least slight strengthening
during that time. Although the shear is expected to remain low
through the remainder of the forecast period, Marty will be moving
over sub-26C SSTs and into a drier and more stable airmass. Those
unfavorable environmental conditions should combine to erode the
central deep convection and weaken the cyclone on days 3 and 4.
Marty is forecast to become a depression on Wednesday, degenerate
into a remnant low on Thursday, and dissipate on Friday. The
official intensity forecast is essentially just an update of the
previous NHC forecast, and is about 5 kt above all of the available
intensity guidance through 60 hours.
FORECAST POSITIONS AND MAX WINDS
INIT 23/1500Z 20.5N 112.4W 35 KT 40 MPH
12H 24/0000Z 20.6N 114.5W 40 KT 45 MPH
24H 24/1200Z 20.6N 117.2W 40 KT 45 MPH
36H 25/0000Z 20.5N 119.3W 35 KT 40 MPH
48H 25/1200Z 20.4N 121.3W 30 KT 35 MPH
60H 26/0000Z 20.3N 123.3W 25 KT 30 MPH...POST-TROP/REMNT LOW
72H 26/1200Z 20.2N 125.5W 20 KT 25 MPH...POST-TROP/REMNT LOW
96H 27/1200Z 19.3N 130.4W 20 KT 25 MPH...POST-TROP/REMNT LOW
120H 28/1200Z...DISSIPATED
$$
Forecaster Stewart
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