525
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
FORECASTER ROBERTS
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