917
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
FORECASTER PAPIN
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