Tropical Cyclone Discussion

992
WTPZ45 KNHC 080855
TCDEP5
 
Tropical Storm Simon Discussion Number   4
NWS National Hurricane Center Miami FL       EP202026
300 AM CST Thu Oct 08 2026
 
This evening's conventional satellite imagery and a recent ASCAT
overpass and a 0323 UTC MetOp-SG1 MI indicate that Simon is
developing a compact inner core structure.  There are also curved
bands with -73C to -82C cold cloud tops forming in the west and
northeast portions of the cyclone.  The TAFB subjective satellite
intensity estimate is T3.0/45 kt and a blend of the UW-CIMSS
objective estimates (41-47 kt) yield an initial intensity of 45 kt.
 
The shear is low, the atmosphere is moist, and the ocean is warm
with high heat content values, all contributing to a high
probability of Simon quickly intensifying during the next couple of
days.  The upper wind pattern is also quite favorable with 
impressive diffluent easterly flow ventilating the western portion 
of the cyclone.  The latest SHIPS RI Index shows a 63 percent 
chance of a 55 kt increase in 48 hrs, while the UW-CIMSS AI-RI 
indicates a similar likelihood of rapid intensification.  The 
official forecast shows Simon becoming a major hurricane in 48 hrs 
with a peak intensity of 115 kt on Saturday, and this is based on 
the HFIP-HCCA and slightly above the Google DeepMind ensemble 
guidance.
 
Simon's initial motion is estimated to be due west, or 270 degrees 
at 6 kt.  This general motion should continue through today while 
being steered by high pressure north of the cyclone over central 
Mexico.  On Friday, the system should turn west-northwestward to 
north-northwestward in response to a mid-tropospheric trough 
approaching Baja California.  Toward the end of the period, Simon is 
expected to move northward ahead of and on the southeastern side of 
the aforementioned trough and approach the southwestern coast of 
Mexico over the weekend.  The GFS and the ECMWF HiRes global models 
still show outlier tracks to the left of the NHC forecast but have 
been trending eastward, aligning more with the better-performing 
HCCA and Google DeepMind TC ensemble mean aids, which the official 
forecast leans toward.
 
Simon's 34 kt wind radii were decreased a bit based on a 0403 UTC
METOP-B ASCAT pass.
 
 
Key Messages:
 
1. Simon is expected to strengthen into a hurricane by early Friday 
and approach the west-central coast of Mexico as a major hurricane 
on Saturday. Tropical storm conditions are possible within the 
tropical storm watch area early Friday. There is also risk of 
dangerous wind and storm surge impacts along portions of this coast 
over the weekend and into early next week and additional watches 
will likely be required for portions of southwestern Mexico.
 
2. Heavy rainfall associated with Simon will impact portions of 
southwestern Mexico later this week and into the weekend. This 
rainfall may produce life-threatening flooding and mudslides, 
especially in areas of steep terrain.
 
3. Swells will affect portions of the southwestern and west-central
coast of Mexico through the weekend.  These swells are likely to
cause life-threatening surf and rip current conditions.  Please
consult products from your local weather office.
 
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  08/0900Z 15.4N 103.1W   45 KT  50 MPH
 12H  08/1800Z 15.4N 104.1W   60 KT  70 MPH
 24H  09/0600Z 15.9N 105.1W   75 KT  85 MPH
 36H  09/1800Z 16.6N 105.5W   95 KT 110 MPH
 48H  10/0600Z 17.4N 105.6W  110 KT 125 MPH
 60H  10/1800Z 18.3N 105.4W  115 KT 130 MPH
 72H  11/0600Z 19.3N 105.3W  110 KT 125 MPH
 96H  12/0600Z 21.8N 105.7W   80 KT  90 MPH
120H  13/0600Z 24.3N 106.1W   55 KT  65 MPH...INLAND