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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 issued 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
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