000
WTPZ43 KNHC 152052
TCDEP3
 
Tropical Depression Thirteen-E Discussion Number   1
NWS National Hurricane Center Miami FL       EP132022
400 PM CDT Thu Sep 15 2022
 
Visible satellite imagery and a couple of recent partial ASCAT 
overpasses indicate that the circulation associated with the area 
of low pressure located south of the Gulf of Tehuantepec has become 
better defined.  A curved band of convection is located over the 
western and southwestern portions of the circulation and has enough 
organization to designate the system as a tropical depression.  The 
ASCAT-C instrument measured peak winds of 25-27 kt over the  
southeastern portion of the circulation and since stronger winds 
likely exist within the convection, the initial intensity is set at 
30 kt.  This is a little above the latest Dvorak estimate of T1.5 
(25 kt) from TAFB.  

Since the cyclone is still in its formative stage, the initial 
motion is a highly uncertain 310/3 kt. The depression is forecast 
to move generally northwestward during the next few days around the 
eastern portion of monsoonal flow that is established over the 
eastern Pacific south of Mexico. As this flow strengthens during 
the next day or so, the depression should move northwestward at an 
increasingly faster forward speed, and the center of the cyclone is 
forecast to approach the southern coast of Mexico on Saturday. The 
GFS and ECMWF models have come into better agreement on the general 
heading of the system, but there are some differences regarding how 
much the cyclone accelerates.  The ECMWF is on the faster side of 
the guidance and brings the center onshore about 6-12 hours sooner 
than the GFS.  The NHC track is between these solutions and is 
along the eastern side of the model trackers.  It should be noted 
that the global model trackers appear to be latching onto another 
low-level vorticity center that is embedded within the monsoonal 
flow after 48 hours.  As a result, the NHC track forecast more 
closely follows the model fields from the various global models. 

The depression is located over warm waters and within a moist 
environment, however moderate northeasterly shear is forecast to 
persist over the system during the next couple of days.  This shear 
is likely to prevent significant intensification, but gradual 
strengthening is anticipated.  The NHC forecast calls for the 
depression to become a tropical storm tonight or Friday and shows 
some additional modest increase in strength before the center 
reaches the coast. Rapid weakening should occur after landfall. The 
NHC intensity forecast is a little below the SHIPS model and IVCN 
consensus aids due to the current broad wind field and expected 
shear conditions.

Based on this forecast, the government of Mexico has issued a 
tropical storm watch for a portion of the coast of southern Mexico. 

Key Messages:

1. Heavy rains will reach portions of coastal southern Mexico on 
Friday, increasing in coverage and intensity by Saturday and 
Saturday night.  This rainfall may produce flash and urban 
flooding, along with isolated mudslides in areas of higher terrain. 

2. Tropical storm conditions are possible along the coast of 
southern Mexico between Laguna de Chacahua and Zihautenajo beginning 
on Saturday and a Tropical Storm Watch has been issue for that 
area. 


FORECAST POSITIONS AND MAX WINDS
 
INIT  15/2100Z 12.7N  95.4W   30 KT  35 MPH
 12H  16/0600Z 13.3N  96.1W   35 KT  40 MPH
 24H  16/1800Z 14.1N  97.4W   40 KT  45 MPH
 36H  17/0600Z 15.1N  98.8W   45 KT  50 MPH
 48H  17/1800Z 16.9N 100.5W   50 KT  60 MPH
 60H  18/0600Z 18.4N 101.9W   30 KT  35 MPH...INLAND
 72H  18/1800Z...DISSIPATED
 
$$
Forecaster Brown