821
WTPZ45 KNHC 121459
TCDEP5
HURRICANE SIMON DISCUSSION NUMBER 21
NWS NATIONAL HURRICANE CENTER MIAMI FL EP202026
800 AM MST MON OCT 12 2026
SIMON'S INTERACTION WITH THE COAST OF MEXICO HAS MADE IT A VERY
COMPACT HURRICANE. THE SATELLITE PRESENTATION THIS MORNING CONSISTS
OF A VERY SMALL CENTRAL DENSE OVERCAST WITH A WARM SPOT IN THE
CENTER WHICH STILL APPEARS TO BE A SMALL EYE. THE CONVECTION IS ALSO
VERY ELECTRICALLY ACTIVE, WITH SUBSTANTIAL LIGHTNING OCCURRING IN
THE EASTERN EYEWALL. A 1110 UTC GPM MICROWAVE PASS SHOWED THAT
SIMON'S INNER CORE REMAINS INTACT, THOUGH WITH THE EYE OPEN ON THE
NORTHWEST SIDE. THIS STRUCTURE IS CONSISTENT WITH SOME MID-LEVEL
EASTERLY SHEAR THAT APPEARS TO BE UNDERCUTTING THE OUTFLOW LAYER,
LOOKING AT SOME AREA-AVERAGE SOUNDINGS FROM THE HAFS-A/B
INITIALIZATION THIS MORNING. SATELLITE INTENSITY ESTIMATES HAVE A
LARGE RANGE THIS MORNING, AS LOW AS CI 4.1/67 KT FROM THE UW-CIMSS
ADT, OR AS HIGH AS CI 5.5/102 KT FROM THE LATEST SUBJECTIVE DVORAK
FIX. THE INITIAL INTENSITY IS LOWERED SLIGHTLY TO 95 KT FOR THIS
ADVISORY, FAVORING A BLEND OF THE LATEST SATCON (100 KT) AND D-MINT
(85-90 KT) ESTIMATES.
BASED ON SATELLITE IMAGES, SIMON CONTINUES TO MOVE VERY SLOWLY TO
THE NORTHWEST, WITH AN ESTIMATED MOTION OF 315 DEGREES AT 3 KT. THIS
VERY SLOW MOTION IS THE RESULT OF COMPETING STEERING INFLUENCES FROM
A DISTANT MID-LEVEL RIDGE CENTERED OVER THE TEXAS GULF COAST, AND
ANOTHER WEAKER MID-LEVEL RIDGE PLACED SOUTHWEST OF SIMON OVER THE
EASTERN PACIFIC. IN GENERAL THE STEERING IMPARTED BY THE RIDGE TO
THE NORTHWEST SHOULD BE A LITTLE STRONGER, AND THUS SIMON IS
EXPECTED TO MAINTAIN A VERY SLOW NORTHWESTWARD MOTION OVER THE NEXT
24-36 H. AFTER THAT PERIOD, A LARGE TROUGH WITH AN EMBEDDED
SHORT-WAVE IS EXPECTED TO AMPLIFY AND MOVE INTO THE SOUTHWESTERN
UNITED STATES, AND THIS TROUGH IS EXPECTED TO EXTEND FAR ENOUGH
SOUTHWARD TO IMPART A LITTLE MORE WESTERLY FLOW THAT SHOULD
ULTIMATELY TURN SIMON TO THE NORTH-NORTHEAST IN THE 48-72 HOUR TIME
FRAME. WITH THAT SAID, THE TRACK GUIDANCE IS NOT AT ALL IN AGREEMENT
ON HOW QUICKLY THIS TURN WILL OCCUR. THE LATEST 06 UTC GFS AND
HAFS-A/B RUNS ALMOST IMMEDIATELY MOVE SIMON NORTHWARD AND THEN
NORTH-NORTHEAST, RESULTING IN A MUCH FASTER LANDFALL BACK IN
MAINLAND MEXICO. BY CONTRAST, THE 06 UTC ECMWF RUN SHOWS A
SHORT-TERM WESTWARD TRACK THAT MEANDERS OFFSHORE TO THE SOUTHEAST OF
THE BAJA CALIFORNIA PENINSULA BEFORE IT TURNS NORTHWARD AND MOVES UP
INTO THE GULF OF CALIFORNIA. THE ENSEMBLE GUIDANCE IS ALSO ALL OVER
THE PLACE, RESEMBLING A SQUASHED SPIDER WITH SUBSTANTIAL SPREAD FROM
THE SOUTHWEST TO NORTHEAST DIRECTION. THE LATEST NHC TRACK FORECAST
HAS BEEN SHIFTED WESTWARD AND IS QUITE A BIT SLOWER, FOLLOWING THE
LATEST TRENDS IN THE TRACK GUIDANCE. HOWEVER, THIS TRACK IS NOT
NEARLY AS SLOW OR AS FAR WEST AS THE LATEST GOOGLE DEEPMIND ENSEMBLE
MEAN (GDMI) OR ITS NEWER WEATHER NEXT MODEL (WN3I). GIVEN THE LARGE
SPREAD IN SOLUTIONS, THIS REMAINS A LOW CONFIDENCE TRACK FORECAST.
BASED ON THE EARLIER MICROWAVE IMAGES, SIMON STILL APPEARS TO HAVE A
SMALL INNER CORE, AND THAT IS AN IMPORTANT CONSIDERATION TO TAKE
INTO ACCOUNT IN THE FORECAST OVER THE NEXT FEW DAYS. WHILE THE
HURRICANE APPEARS TO BE CURRENTLY DEALING WITH SOME MID-LEVEL
EASTERLY SHEAR AND THAT MAY RESULT IN A LITTLE MORE SHORT-TERM
WEAKENING, THIS SHEAR IS EXPECTED TO SUBSIDE OVER THE NEXT 24 H AS
SIMON TRAVERSES VERY WARM 30-31 C SEA-SURFACE TEMPERATURES. IN FACT,
THE LATEST HMON AND HAFS-A/B RUNS SHOW THE SMALL CORE OF SIMON
RECOVERING AND RE-INTENSIFYING BACK INTO A MAJOR HURRICANE LATER
THIS WEEK. THUS, THE LATEST NHC INTENSITY FORECAST STARTS TO SHOW
SOME RESTRENGTHENING AFTER 24 H. SMALL STORMS LIKE SIMON CAN ALSO
BE PRONE TO RAPID CHANGES IN INTENSITY, BOTH UP OR DOWN, WHICH
MAKES THE INTENSITY FORECAST ALSO MORE UNCERTAIN THAN USUAL. THIS
FORECAST IS INITIALLY CLOSE TO THE MIDDLE OF THE GUIDANCE BUT ENDS
UP ON THE HIGHER SIDE AFTER 48 H. RAPID WEAKENING IS STILL
ANTICIPATED WHEN SIMON EVENTUALLY MAKES LANDFALL LATER THIS WEEK
TOWARDS THE END OF THE FORECAST.
KEY MESSAGES:
1. TROPICAL STORM WINDS ARE STILL LIKELY ALONG A PORTION OF THE
WEST-CENTRAL COAST OF MEXICO FOR A FEW MORE HOURS, WHERE A TROPICAL
STORM WARNING IS IN EFFECT.
2. SIMON IS EXPECTED TO APPROACH THE COAST OF WESTERN MEXICO LATER
THIS WEEK, WHERE HURRICANE CONDITIONS ARE POSSIBLE. A HURRICANE
WATCH IS IN EFFECT FROM CABO CORRIENTES TO BAHIA TEMPEHUAYA.
3. HEAVY RAINFALL ASSOCIATED WITH SIMON WILL IMPACT PORTIONS OF
SOUTHWESTERN AND 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 FEW 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 12/1500Z 20.1N 106.5W 95 KT 110 MPH
12H 13/0000Z 20.4N 106.8W 85 KT 100 MPH
24H 13/1200Z 20.9N 107.3W 80 KT 90 MPH
36H 14/0000Z 21.3N 107.7W 85 KT 100 MPH
48H 14/1200Z 21.6N 107.7W 90 KT 105 MPH
60H 15/0000Z 22.2N 107.4W 90 KT 105 MPH
72H 15/1200Z 23.2N 106.9W 90 KT 105 MPH
96H 16/1200Z 24.1N 106.3W 45 KT 50 MPH...INLAND
120H 17/1200Z...DISSIPATED
FORECASTER PAPIN
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