Tropical Storm John Forecast Discussion

521 
WTPZ45 KNHC 270900
TCDEP5

Tropical Storm John Discussion Number  18
NWS National Hurricane Center Miami FL       EP102024
300 AM CST Fri Sep 27 2024

This morning's satellite presentation consists of a partially
exposed surface center with a primary banding feature wrapping
around from the southeast.  A few fragmented intermittent bursts of
deep convection are also evident in the northwest quadrant of the
cyclone.  The initial intensity is set at 55 kt and is based on
the TAFB and SAB Dvorak satellite intensity estimates and a
UW-CIMSS DMINT objective estimate using SSMIS F16-17 passes of 56
and 55 kt, respectively.

Gradual weakening should continue as the cyclone approaches and
moves inland. The high terrain of the Sierra Madre Del Sur
mountains is expected to disrupt what remains of John's inner 
core and should cause a faster rate of weakening.  Therefore, John 
is expected to become a remnant low in 36 hrs.  If the surface 
center remains intact and doesn't dissipate, the remnants should 
re-emerge over the water in a few days; however, regeneration 
appears unlikely. The NHC intensity forecast is weighed heavily on 
the global model guidance and the IVCN intensity consensus.

John's initial motion is estimated to be northwestward, or 320/4
kt, and a turn to the west-northwest with a slight increase in
forward speed is forecast, provided John survives its interaction
with the rugged mountainous terrain.  The track forecast favors a
compromise of the global model solutions and is just to the right
of the HCCA consensus aid.


KEY MESSAGES:

1. Tropical Storm John will bring additional very heavy rainfall to 
coastal portions of southwest Mexico through today. 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 today.


FORECAST POSITIONS AND MAX WINDS

INIT  27/0900Z 17.8N 102.9W   55 KT  65 MPH
 12H  27/1800Z 18.6N 103.6W   40 KT  45 MPH
 24H  28/0600Z 19.3N 104.8W   30 KT  35 MPH
 36H  28/1800Z 19.6N 106.2W   25 KT  30 MPH...POST-TROP/REMNT LOW
 48H  29/0600Z 20.3N 107.6W   25 KT  30 MPH...POST-TROP/REMNT LOW
 60H  29/1800Z...DISSIPATED

$$
Forecaster Roberts