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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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