Tropical Storm John Forecast Discussion

000
WTPZ45 KNHC 260909
TCDEP5

Tropical Storm John Discussion Number  14
NWS National Hurricane Center Miami FL       EP102024
300 AM CST Thu Sep 26 2024

Recent TROPICS/TMS and SSMIS microwave passes indicated
an improved inner core with a 70 percent closed small eye feature.
The UW-CIMSS objective intensity guidance ranges from 56 to 65 kt, 
and the latest SATCON analysis indicated an intensity of 61 kt. The 
subjective satellite estimates from TAFB and SAB are 65 and 55 kt, 
respectively. The initial intensity is set at 60 kt using a blend 
of these data.

The ocean sea surface temperatures are very warm, and the shear is
low, and there is ample moisture in the low to mid-portions of the
atmosphere for John to quickly strengthen before the cyclone moves
over the coast on Friday.  The UW-CIMSS AI RI index and the SHIPS
statistical-dynamical RI model both continue to show increasing
chances of John quickly strengthening during the next 24 hrs and
the NHC intensity forecast follows suit and shows a peak of 85 kt 
before landfall.

The initial motion is estimated to be west-northwestward, or   
285/3 kt and is being steered by a mid-tropospheric ridge centered 
over Northern Mexico.  John should continue in this general motion 
is expected to continue today, followed by a gradual turn to the 
northwest by this evening.  On the forecast track, the center of 
John is forecast to approach and move along the coast of 
southwestern Mexico or just inland on Friday.  The official track 
forecast is adjusted to a little to the left of the previous one and 
follows a compromise of the skilled HCCA consensus model and the 
ECMWF global model, which has been performing the best with this 
system.

The wind radii have been adjusted for this advisory, and was based
on a 0426 UTC METOP-C scatterometer overpass.

It cannot be emphasized enough that catastrophic life-threatening
flash flooding and mudslides are expected to continue through the
end of the week for portions of the Mexican States of Guerrero,
Oaxaca and Michoacan.


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 and Michoacan.

2. John is forecast to strengthen to a hurricane before landfall,
and a Hurricane Warning is in effect along the coastline of 
southwestern Mexico, where tropical storm conditions could begin 
during the next few hours.  Tropical Storm Warnings are also 
in effect for portions of the area and has been extended westward 
to Manzanillo.


FORECAST POSITIONS AND MAX WINDS

INIT  26/0900Z 17.1N 102.5W   60 KT  70 MPH
 12H  26/1800Z 17.2N 102.6W   75 KT  85 MPH
 24H  27/0600Z 17.8N 103.0W   85 KT 100 MPH
 36H  27/1800Z 18.8N 103.6W   45 KT  50 MPH
 48H  28/0600Z 19.7N 104.7W   30 KT  35 MPH
 60H  28/1800Z 20.2N 106.2W   25 KT  30 MPH...POST-TROP/REMNT LOW
 72H  29/0600Z...DISSIPATED

$$
Forecaster Roberts