Tropical Cyclone Discussion

395
WTPZ45 KNHC 152043
TCDEP5
 
Tropical Storm Simon Discussion Number  34
NWS National Hurricane Center Miami FL       EP202026
200 PM MST Thu Oct 15 2026

Simon continues to produce an area of deep convection, though this 
activity has lacked a ton of organization today, and appears to 
still be displaced to the west of the center of circulation. A RCM-2 
synthetic aperture radar (SAR) pass that became available after the 
prior advisory indicated that most of this convective activity was 
also occurring outside of its radius of maximum winds, and has done 
little to aid the small circulation. In fact, the peak winds 
retrieved from the SAR was only 47 kt. This information, combined 
with a Metop-B scatterometer pass that had a peak wind of 39 kt is 
justification to bring Simon's intensity down to 45 kt this 
advisory, and this may still be generous. 

Simon has been drifting rather aimlessly today, and my best guess 
at an estimated motion is 320/1 kt. It has been a tough few days 
trying to forecast Simon's track, but the model guidance this cycle 
is finally coming into better agreement showing that as Simon 
becomes a more vertically shallow cyclone, it will primarily be 
steered by the low-level flow. To that end, a weak low-level trough 
is forecast to drop equatorward to the west of Simon as a strong 
pressure gradient develops over northern Mexico as surface ridging 
builds in behind a frontal boundary. This flow should help to 
finally draw Simon back to the northwest with a speed up in its 
forward motion. The latest NHC track forecast is shifted once again 
a little further west but also faster, following the latest trends 
in the reliable HFIP Corrected Consensus Approach (HCCA) and Google 
DeepMind ensemble mean (GDMI). 

While the shear over Simon is currently low, it has not taken 
advantage of these more favorable conditions, likely due to the 
proximity of dry air preventing the convection from organizing. The 
vertical wind shear is soon expected to increase significantly out 
of the southwest as a deep-layer trough located over the 
southwestern United States cuts off and retrogrades back westward. 
Simon has already been sensitive to less than pristine conditions, 
and this increase in shear will likely be the storm's demise. The 
latest NHC forecast now shows gradual weakening continuing over the 
next 24-36 h, with Simon becoming a remnant low in 48 h, and fully 
dissipating in 72 h. If the latest ECMWF forecast is correct, this 
could occur sooner than forecasted here.
 
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  15/2100Z 19.3N 108.2W   45 KT  50 MPH
 12H  16/0600Z 19.8N 108.7W   40 KT  45 MPH
 24H  16/1800Z 20.8N 110.0W   35 KT  40 MPH
 36H  17/0600Z 22.0N 111.9W   30 KT  35 MPH
 48H  17/1800Z 23.1N 113.6W   25 KT  30 MPH...POST-TROP/REMNT LOW
 60H  18/0600Z 24.5N 115.0W   20 KT  25 MPH...POST-TROP/REMNT LOW
 72H  18/1800Z...DISSIPATED