Tropical Cyclone Discussion

162
WTPZ45 KNHC 102059
TCDEP5
 
Hurricane Simon Discussion Number  14
NWS National Hurricane Center Miami FL       EP202026
300 PM CST Sat Oct 10 2026

Air Force Reserve Hurricane Hunters have been investigating Simon 
this afternoon, finding that the hurricane is indeed a Category 4 
storm. The minimum pressure is estimated to be down to 932 mb, and 
the peak 700 mb flight level winds were 134 kt in the eastern 
quadrant of the hurricane. While a standard 0.9 reduction would 
typically support a 10 meter sustained wind of 120-125 kt, the 
entire wind field of Simon was not fully sampled. In addition, there 
was an earlier partial Synthetic Aperture Radar (SAR) RCM-1 pass 
which had a peak wind of 138 kt. Satellite intensity estimates, 
which have been lagging behind the estimated intensity of Simon, 
have also risen somewhat today. Taking all these data points 
together, the initial intensity is held at 130 kt this advisory. The 
aircraft also reported concentric eyewalls, with the inner eyewall 
12 n mi and outer wall at 36 n mi. Some concentric bands were also 
picked up by a recent AMSR-3 microwave pass. 
 
After slowing down to a crawl earlier, aircraft fixes indicate that 
Simon starting to move due north again, with an estimated motion at 
360/4 kt. As previously discussed, the hurricane is being primarily 
steered by a weak mid-level ridge to the east, providing deep-layer 
southerly flow. A subtle narrow mid-level ridge to the northwest is 
also imparting a slight amount of northerly flow. Once again, the 
track guidance this afternoon has made a slower adjustment. In 
addition, there is a bit of an eastward shift in the guidance 
envelope. One notable change from this morning, now all the 
hurricane-regional model runs (HWRF, HMON, HAFS-A, HAFS-B) all show 
Simon making landfall in Jalisco in 24-36 h. In addition, both the 
Google DeepMind ensemble mean (GDMI) and its upgraded Weather Next 
model (WN3I) also nudged their tracks eastward. Thus, the NHC track 
forecast has shifted a bit to the east, but still lies on the 
eastern end of the guidance. Part of the reason for favoring the 
eastern edge of the guidance is that there is a pretty well-known 
bias that tropical cyclones in this area tend to track east of the 
forecast track due to interaction with the high topography of 
coastal Mexico.

As mentioned this morning, the future intensity forecast of Simon is 
heavily influenced by Simon's ultimate track. Because large-scale 
environmental conditions remain favorable, Simon's short-term 
intensity forecast will likely be controlled by inner-core 
fluctuations, like eyewall replacement cycles. This is pertinent 
given the concentric eyewalls noted by the aircraft mission. 
However, as Simon nears the Mexican coast, the high topography will 
interact with the hurricane's outer circulation, and spot soundings 
in the HAFS-A/B runs show evidence of downslope subsidence occurring 
as Simon nears landfall. This effect will both cause the hurricane's 
wind field to shrink in size, and will likely result in weakening 
even before the hurricane makes landfall in Mexico. Weakening is 
expected to begin between 12-24 h, with more substantial weakening 
occurring when Simon moves fully onshore. Once again, this intensity 
forecast is quite uncertain. If Simon remains offshore, like the 
ECMWF and a decent chunk of GDM ensemble members show, it may remain 
much stronger than the latest NHC intensity forecast. The latest 
forecast is a bit lower than the prior one, with a bit more 
confidence that Simon will move inland, though the latest forecast 
still shows Simon dissipating over Mexico after 60 h.
 
Key Messages:
 
1. Catastrophic wind and life-threatening storm surge impacts are 
likely along a portion of the west-central coast of Mexico, and a 
Hurricane Warning is in effect from Punta San Telmo to El Roblito. 
Preparations to protect life and property should be completed this 
afternoon.
 
2. Heavy rainfall associated with Simon will impact portions of 
southwestern Mexico through this weekend. This rainfall will 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  10/2100Z 17.6N 104.8W  130 KT 150 MPH
 12H  11/0600Z 18.3N 104.9W  130 KT 150 MPH
 24H  11/1800Z 19.4N 105.1W  110 KT 125 MPH
 36H  12/0600Z 20.8N 105.2W   70 KT  80 MPH...INLAND
 48H  12/1800Z 21.9N 105.2W   45 KT  50 MPH...INLAND
 60H  13/0600Z 22.8N 105.1W   15 KT  15 MPH...POST-TROP/INLAND
 72H  13/1800Z...DISSIPATED