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Tropical Storm Marty Discussion Number   1
NWS National Hurricane Center Miami FL       EP132021
300 AM MDT Mon Aug 23 2021
 
Recent scatterometer wind data indicate that the circulation 
associated with the low pressure area located a couple of hundred 
miles south-southwest of the southern tip of the Baja California 
peninsula has become better defined.  In addition, convective 
activity has persisted and expanded over the western portion of the 
circulation overnight, resulting in Dvorak T-numbers of 1.5 and 2.0 
from SAB and TAFB, respectively.  Both ASCAT-A and B instruments 
revealed 30 to 35 kt winds over the western portion of the 
circulation and based on these data, advisories are being initiated 
on Tropical Storm Marty, the thirteenth named-storm of the 2021 
eastern Pacific hurricane season. 

Marty is moving westward at about 13 kt.  A strong mid-tropospheric 
ridge that extends from the south-central United States westward 
across northern Mexico and the eastern Pacific is forecast to steer 
Marty westward over the next couple of days.  After that time, the 
cyclone is forecast to weaken and become vertically shallow.  This 
should cause it to turn toward the west-southwest as it steered by 
the low-level trade wind flow. The dynamical model guidance is in 
excellent agreement, and the NHC track is near the middle of the 
tightly clustered model envelope.

Although the tropical storm is currently located over warm waters, 
it is within an area of moderate northeasterly shear.  In addition, 
it is likely to ingest drier and more stable air located to the 
northwest of the system over the next couple of days.  As a result, 
only slight strengthening is indicated in the official forecast.  
By 36 hours, Marty is forecast to cross the 26C isotherm and 
gradual weakening is anticipated after that time.  Less favorable 
thermodynamic conditions should result in the system becoming a 
remnant low in 60 to 72 hours, if not sooner.  The NHC intensity 
forecast is in good agreement with the HCCA and IVCN consensus 
aids. 
 
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  23/0900Z 20.0N 111.0W   35 KT  40 MPH
 12H  23/1800Z 20.3N 113.2W   40 KT  45 MPH
 24H  24/0600Z 20.4N 116.0W   40 KT  45 MPH
 36H  24/1800Z 20.2N 118.4W   35 KT  40 MPH
 48H  25/0600Z 20.1N 120.4W   30 KT  35 MPH
 60H  25/1800Z 20.0N 122.3W   25 KT  30 MPH...POST-TROP/REMNT LOW
 72H  26/0600Z 19.8N 124.3W   20 KT  25 MPH...POST-TROP/REMNT LOW
 96H  27/0600Z 19.0N 129.2W   20 KT  25 MPH...POST-TROP/REMNT LOW
120H  28/0600Z...DISSIPATED
 
$$
Forecaster Brown
 
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