Tropical Cyclone Discussion

377
WTPZ45 KNHC 130255
TCDEP5
 
Hurricane Simon Discussion Number  23
NWS National Hurricane Center Miami FL       EP202026
800 PM MST Mon Oct 12 2026
 
Simon's convection has degraded quite a bit since the last advisory.
Given how much of this weakening has been concentrated across the
eastern half of the storm, it is possible that Simon has been
ingesting dry, high terrain air into its center. Regardless of the
physical mechanism, however, both subjective and objective Dvorak
intensity estimates have picked up on this weakening trend, as the
TAFB Dvorak classification rates Simon at 5.0/90 kt and UW-CIMSS
estimates range from 51 to 72 kt. As a result of these data, Simon's
initial intensity has been lowered to 85 kt.
 
The storm motion remains very slow at 305/3 kt. Simon is riding the
western flank of a high pressure ridge centered over the
southeastern US, with high pressure building to the storm's west as
well in the wake of a deep trough currently enveloping the
Intermountain West. Simon is battling a multitude of features
influencing its motion as a result, and track guidance continues to
exhibit a wide spread of solutions. Thus, confidence in the track
forecast remains low. The global models, however, do seem to agree
that the high anchored over the southeastern US will remain for at
least the next 48 hours, so the current forecast thinking is that
Simon will not make a turn toward land in the meantime. What becomes
of that high once the aforementioned trough moves eastward across
the US is what will ultimately determine Simon's path.
 
Looking at the global models, the GFS depicts the trough doing
little to erode the southeastern high, leaving Simon to become
caught in a col as it is wedged between two high pressure systems,
thus causing it to become nearly stationary over the next couple of
days. The ECMWF, however, seems to suggest that the trough will dig
deep enough to cause a turn to the northeast toward land over the
next 48 hours. More skilled guidance like the HCCA and GDMI,
however, seem to favor a due northwest track, likely stemming from
the southeastern US high remaining fixed in place and the high to
the west not building enough to affect Simon's motion. The latest
NHC track forecast favors this solution, while still depicting a
turn to the northeast after a couple of days should this Pacific
high strengthen enough to nudge Simon off its current trajectory.
 
Should Simon continue to move northwestward, as is currently
forecast, gradual re-strengthening should follow. The environment
just off the coast of west-central Mexico continues to be defined by
low vertical wind shear, anomalously warm SSTs, and ample mid-level
moisture. Should the storm become nearly stationary as some models
suggest, however, re-intensification could be inhibited by Simon
churning up cooler waters from deep below the sea surface. It should
be noted that the current consensus across the guidance does not
favor a period of rapid intensification, so the latest NHC intensity
forecast continues to reflect a more gradual upward trend in
strength, before dropping off sharply once Simon makes its
forecasted approach to land. With confidence lacking in the track
forecast, however, Simon's intensity forecast confidence is only low
to moderate.
 
Key Messages:
 
1. Hurricane conditions are likely on Las Islas Marias over the
next day or so, where a Hurricane Warning remains in effect.
 
2. Simon could approach the coast of western Mexico later this week,
where hurricane conditions are possible.
 
3. Heavy rainfall associated with Simon will impact portions of
west-central Mexico over the next few days. This rainfall will
produce life-threatening flooding and mudslides, especially in areas
of steep terrain.
 
4. Large swells will affect portions of the southwestern and
west-central coasts of Mexico over the next several days. 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  13/0300Z 20.4N 107.0W   85 KT 100 MPH
 12H  13/1200Z 20.7N 107.3W   75 KT  85 MPH
 24H  14/0000Z 21.0N 107.7W   70 KT  80 MPH
 36H  14/1200Z 21.3N 108.0W   70 KT  80 MPH
 48H  15/0000Z 21.8N 108.0W   75 KT  85 MPH
 60H  15/1200Z 22.5N 107.9W   80 KT  90 MPH
 72H  16/0000Z 23.2N 107.8W   85 KT 100 MPH
 96H  17/0000Z 24.0N 107.6W   85 KT 100 MPH
120H  18/0000Z 24.8N 107.3W   30 KT  35 MPH...POST-TROP/INLAND