Tropical Storm John Forecast Discussion

000
WTPZ45 KNHC 270235
TCDEP5

Tropical Storm John Discussion Number  17
NWS National Hurricane Center Miami FL       EP102024
900 PM CST Thu Sep 26 2024

The convection near the center of John has weakened significantly 
over the past 12 hours.  A curved band off to the southwest and west 
of John's center is producing a continuous large area of deep 
convection.  Subjective Dvorak current intensity estimates from TAFB 
and SAB range from 65 to 77 kt, but the objective intensity 
estimates from UW-CIMSS range from 49 to 56 kt. Since the convection 
over the center has warmed on infrared imagery and appears to be 
less organized over the past 12 hours, the initial intensity is 
being lowered to 60 kt for this advisory.

John has been moving northwestward, or 315/4 kt, which is a bit 
faster than before.  This slow motion is forecast to continue for 
another 12 to 24 h, as John moves near the coastline or just inland 
late tonight and early tomorrow.  After that, a turn to the 
west-northwest with some acceleration is forecast, if John survives 
its interaction with the higher topography in this part of Mexico.  
The latest track forecast is a little to the left and slightly 
faster than the previous forecast, and is very near the lastest HCCA 
corrected consensus aid.

It seems unlikely that John will be able to restrengthen since the 
center is now just 20 miles from the coastline and is forecast to 
move even closer to the coast over the next several hours.  Since 
John's core has been disrupted by the topography today, it is 
unlikely to recover, despite relatively favorable environmental 
conditions.  Little change in strength, or perhaps slow weakening, 
is likely over the next 12 hours until the center reaches the 
coastline. Thereafter, faster weakening is expected on Friday as the 
center moves near or along the coastline.  The latest NHC intensity 
forecast is near the middle of the intensity guidance suite.  It is 
quite possible that John could weaken to a remnant low and dissipate 
sooner than forecast. 


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 and
Michoacán.

2. John is forecast to continue bringing tropical storm conditions 
across portions of the Tropical Storm Warnings area through Friday.


FORECAST POSITIONS AND MAX WINDS

INIT  27/0300Z 17.9N 103.2W   60 KT  70 MPH
 12H  27/1200Z 18.3N 103.4W   55 KT  65 MPH...INLAND
 24H  28/0000Z 19.0N 104.4W   35 KT  40 MPH...OVER WATER
 36H  28/1200Z 19.5N 105.7W   25 KT  30 MPH
 48H  29/0000Z 20.2N 107.0W   25 KT  30 MPH...POST-TROP/REMNT LOW
 60H  29/1200Z 20.8N 108.6W   20 KT  25 MPH...POST-TROP/REMNT LOW
 72H  30/0000Z...DISSIPATED

$$
Forecaster Hagen