Tropical Storm John Forecast Discussion

000
WTPZ45 KNHC 230853
TCDEP5

Tropical Storm John Discussion Number   3
NWS National Hurricane Center Miami FL       EP102024
300 AM CST Mon Sep 23 2024

Satellite images indicate that John continues to become better 
organized, with very deep convection near the center and some tight 
curved band features.  Earlier microwave imagery also showed some 
inner core development, with perhaps a partial eyewall trying to 
form.  Subjective Dvorak estimates at 06z were 35 kt from both 
TAFB/SAB, though the objective values were between 40-50 kt.  The 
intensity is set to 40 kt as a blend of these data.

The storm is moving slowly to the north-northeast, caught in the 
large-scale southwesterly flow associated with the monsoon trough 
near Central America.  There has been a big change in most of the 
track guidance since yesterday, with a fair number of the models 
now showing a steadier northeastward motion with less eastward 
steering from the incipient tropical cyclone in the northwestern 
Caribbean Sea.  Consequently, the models have shifted leftward and 
faster.  The official forecast is also trended in that direction, 
but could still be too far to the east.  

John is forecast to be over very warm waters with light shear while 
it approaches the coast of Mexico over the next day or so.  While 
none of the regional hurricane models make John a hurricane before 
landfall, the rapid intensification indices are indicating at least 
a 50 percent chance that this system strengthens 30 kt in the next 
24 hours, which would indicate hurricane-strength.  Given the 
uncertainties involved, a Hurricane Watch and a Tropical Storm 
Warning have been issued by the government of Mexico for portions of 
the coast of southern Mexico on this advisory, and interests there 
should closely monitor for future forecast updates.


KEY MESSAGES:

1. Slow-moving Tropical Storm John will bring very heavy
rainfall to coastal portions of southwest Mexico through the
upcoming week.  This heavy rainfall will likely cause significant
and possibly catastrophic, life-threatening flash flooding and
mudslides to the Mexican States of Chiapas, Oaxaca, and southeast
Guerrero, particularly in areas near the coast.

2. John is forecast to strengthen before landfall, and a Hurricane 
Watch and a Tropical Storm Warning have been issued for a portion 
of the coastline of southern Mexico, where tropical storm 
conditions could begin late today.

3. John could strengthen more than forecast depending on how
long it remains over water. Interests along the coast of southern
Mexico should monitor the latest forecast updates, as Hurricane
Warnings could be required for a portion of the coastline later 
today.


FORECAST POSITIONS AND MAX WINDS

INIT  23/0900Z 14.4N  98.5W   40 KT  45 MPH
 12H  23/1800Z 14.8N  98.2W   50 KT  60 MPH
 24H  24/0600Z 15.4N  97.6W   60 KT  70 MPH
 36H  24/1800Z 15.8N  97.2W   60 KT  70 MPH
 48H  25/0600Z 16.0N  97.0W   45 KT  50 MPH...INLAND
 60H  25/1800Z...DISSIPATED

$$
Forecaster Blake