Tropical Storm John Forecast Discussion

000
WTPZ45 KNHC 251456
TCDEP5

Tropical Storm John Discussion Number  11
NWS National Hurricane Center Miami FL       EP102024
900 AM CST Wed Sep 25 2024

John has reformed near the southwestern coast of Mexico.  The 
CIMSS-UW satellite vorticity analyses show remnants of vorticity, 
likely associated with the mid-level circulation of John, have 
merged with a larger source of vorticity from the monsoon trough.  
Convection has gradually become better organized based on 
geostationary infrared and visibly imagery.  An AMSR2 microwave pass 
at 0807 UTC showed curved banding near the surface, indicating a 
well-defined surface center. A Dvorak classification from TAFB has 
given John a 2.0/35 kt and that is the initial intensity for this 
advisory. 

The environmental conditions appear conducive for John to strengthen 
in the next day or so, as long as the circulation stays over water.  
Global models show the vertical wind shear remaining 
weak-to-moderate, ample mid-level moisture, and very warm sea 
surface temperatures.  Statistical guidance even suggests there is 
an above average possibility for strong-to-rapid intensification.  
The latest NHC intensity forecast shows John reaching a peak 
intensity of 55 kt in 24 h, which is near the HCCA intensity aid and 
at the top of the guidance envelope.  However, there is a chance 
John may become a hurricane prior to landfall.

The tropical storm is meandering eastward in the monsoonal flow with 
an estimate motion of 80/2 kt.  Models indicate that John will 
gradually turn towards the north later today and accelerate slightly 
towards the coast on Thursday.  Regional and global models vary the 
timing of landfall, with the GFS and GFS-based hurricane models 
showing John at the coast by tomorrow evening and the ECMWF 
lingering offshore until Friday.  The official track forecast calls 
for landfall along the southern and southwestern coast of Mexico on 
Thursday evening, however, there is uncertainty associated with this 
timing.  A Hurricane Watch and Tropical Storm Warning have been 
issued by the government of Mexico for portions of the coast of 
southern Mexico and interests there should closely monitor future 
forecasts for updates.

KEY MESSAGES:

1. Tropical Storm John will bring additional very heavy rainfall to 
coastal portions of southwest Mexico through Friday.  The additional 
rainfall totals will be falling across areas that have received very 
heavy rainfall amounts over the past few days.   This heavy rainfall 
will likely cause significant and  catastrophic, life-threatening 
flash flooding and mudslides to the Mexican States of Guerrero,  
Oaxaca, coastal Chiapas, and coastal Michoaca.

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 and southwestern Mexico, where tropical 
storm conditions could begin later today.

FORECAST POSITIONS AND MAX WINDS

INIT  25/1500Z 16.2N 101.4W   35 KT  40 MPH
 12H  26/0000Z 16.3N 101.2W   45 KT  50 MPH
 24H  26/1200Z 16.7N 101.1W   55 KT  65 MPH
 36H  27/0000Z 17.3N 101.1W   55 KT  65 MPH
 48H  27/1200Z 17.8N 101.2W   30 KT  35 MPH
 60H  28/0000Z...DISSIPATED

$$
Forecaster Bucci/R. Zelinsky