611
WTPZ45 KNHC 122053
TCDEP5
HURRICANE SIMON DISCUSSION NUMBER 22
NWS NATIONAL HURRICANE CENTER MIAMI FL EP202026
200 PM MST MON OCT 12 2026
THIS AFTERNOON, SIMON IS A SMALL HURRICANE THAT IS DEALING WITH SOME
EASTERLY VERTICAL WIND SHEAR. THE INNER-CORE CONTINUES TO PRODUCE A
LOT OF LIGHTNING BUT MOSTLY IN THE EASTERN SEMICIRCLE. THE MOST
RECENT MICROWAVE IMAGE WAS A 1718 UTC AWS PASS THAT ALSO SHOWED THIS
CORE ASYMMETRY WITH THE EYEWALL OPEN ON THE NORTHWEST SIDE ON THE
180 GHZ CHANNEL. WHILE THE LATEST 18 UTC SUBJECTIVE DVORAK ESTIMATE
REMAINS AT CI 5.5/102-KT, THE OBJECTIVE INTENSITY ESTIMATES FROM
UW-CIMSS CONTINUE TO GRADUALLY DECREASE. THUS, THE INITIAL INTENSITY
IS BEING REDUCED TO A SOMEWHAT UNCERTAIN 85 KT THIS ADVISORY, WHICH
ALSO MATCHES THE D-MINT MEAN ESTIMATE FROM THE AWS MICROWAVE PASS
ABOVE. A HELPFUL 1712 UTC METOP-C SCATTEROMETER PASS WAS USEFUL TO
HELP ADJUST SIMON'S RADII AND ALSO TO INDICATE ITS WIND FIELD HAS
BECOME QUITE SMALL, WITH 34-KT WINDS ONLY EXTENDING OUT ABOUT
40 N MI.
SIMON'S TRACK HAS THROWN US A FEW CURVE BALLS OVER THE PAST 24-36 H,
AND THIS AFTERNOON IS NO EXCEPTION AS THE HURRICANE MADE A BRIEF
WESTWARD JOG, WITH THE LONGER-TERM MOTION ESTIMATED AT 290/3 KT. THE
TRACK FORECAST REMAINS PROBLEMATIC. PART OF THE SLOW MOTION SIMON IS
EXHIBITING TODAY IS RELATED TO COMPETING STEERING SYNOPTIC FEATURES,
PRIMARILY A MID-LEVEL RIDGE CENTERED NEAR THE TEXAS COAST VERSUS
ANOTHER MID-LEVEL RIDGE LOCATED SOUTHWEST OF THE HURRICANE. THE
INFLUENCE OF THE NORTHEASTERN RIDGE HAS BEEN A LITTLE STRONGER, BUT
STEERING DIAGNOSTICS SUGGEST THAT SIMON MAY BE SOON REACHING A
BIFURCATION OR COL POINT IN THE FLOW. THIS FEATURE INDICATES THE
AREA WHERE THE NET STEERING FLOW COLLAPSES AND HELPS EXPLAIN WHY
BOTH THE DETERMINISTIC AND ENSEMBLE TRACK GUIDANCE SPREAD INCREASES
QUITE DRAMATICALLY IN 24 TO 48 H. FOR EXAMPLE, THE HAFS-A/B MODELS,
WHICH EARLIER THIS MORNING WERE SHOWING A FASTER NORTHEASTWARD TURN
BACK INTO MEXICO, NOW SHOW SIMON STALLING AND EXECUTING A SLOW
CYCLONIC LOOP IN THE WATERS BETWEEN MAINLAND MEXICO AND THE SOUTHERN
TIP OF THE BAJA CALIFORNIA PENINSULA. THE EUROPEAN ENSEMBLE SPREAD
SUGGESTS THAT THESE INDIVIDUAL SOLUTIONS ARE LIKELY JUST DIFFERENT
FLAVORS OF THE OVERALL DISTRIBUTION, WHICH IS SPREAD OUT IN A
SOUTHWEST TO NORTHEAST FASHION. WHILE THE OVERALL TRACK GUIDANCE
CONTINUES TO HAVE LARGE SPREAD, THERE HAS BEEN A NORTHWARD AND
FASTER SHIFT THIS CYCLE. THIS SHIFT IS A BIT ODD GIVEN THE CURRENT
STORM MOTION, SO THE NHC TRACK FORECAST IS INITIALLY ON THE LEFT
SIDE OF THE GUIDANCE OVER THE FIRST 12-24 H, BUT FALLS BACK CLOSER
TO THE MIDDLE OF THE GUIDANCE ENVELOPE, AND ATTEMPTS TO BLEND THE
LATEST HFIP CORRECTED CONSENSUS APPROACH (HCCA), GOOGLE DEEPMIND
ENSEMBLE MEAN (GDMI), AND THEIR LATEST WEATHER NEXT MODEL (WN3I).
ULTIMATELY THE LATEST TRACK FORECAST CONVERGES CLOSE TO THE PRIOR
ONE NEAR LANDFALL IN MEXICO IN 72-96 H, BUT THIS REMAINS A LOW
CONFIDENCE TRACK FORECAST.
THE INTENSITY FORECAST FOR SIMON IS ALSO CHALLENGING. THE CURRENT
MID-LEVEL EASTERLY SHEAR AFFECTING SIMON'S INNER CORE STRUCTURE HAS
NOT BEEN WELL ANTICIPATED BY THE MODEL GUIDANCE. SMALL TROPICAL
CYCLONES LIKE SIMON ARE OFTEN MORE SENSITIVE TO NEGATIVE
ENVIRONMENTAL FACTORS, AND EVEN 15-20 KT OF EASTERLY SHEAR COULD BE
ENOUGH TO DISRUPT THE CORE STRUCTURE, ESPECIALLY WITH NEARBY
ENVIRONMENTAL DRY AIR. THE FACTORS MAY RESULT IN ADDITIONAL
WEAKENING IN THE SHORT-TERM. HOWEVER, EC-SHIPS GUIDANCE SHOWS THE
SHEAR LOWERING BELOW 5 KT IN 24-48 H. ASSUMING SIMON IS ABLE TO
MAINTAIN AN INNER CORE STRUCTURE AND TAKE ADVANTAGE OF THE MORE
FAVORABLE CONDITIONS, RESTRENGTHENING IS STILL FORECAST, ESPECIALLY
AS THE HURRICANE IS EXPECTED TO TRACK OVER THE WARMEST SEA-SURFACE
TEMPERATURES IN THE EASTERN PACIFIC BASIN (31-32 C). THE INTENSITY
GUIDANCE SHOWS MORE SHORT-TERM WEAKENING COMPARED TO THE PREVIOUS
CYCLE, AND THE NHC INTENSITY FORECAST IS LOWER EARLY ON, BUT STILL
SHOWS RESTRENGTHENING AS SIMON ENCOUNTERS THOSE MORE FAVORABLE
CONDITIONS, AND ENDS UP ON THE HIGH END OF THE INTENSITY GUIDANCE IN
60-72 H. SMALL STORMS LIKE SIMON CAN ALSO BE PRONE TO RAPID CHANGES
IN INTENSITY, WHICH CONTINUES TO MAKE THIS INTENSITY FORECAST ALSO
MORE UNCERTAIN THAN USUAL. RAPID WEAKENING IS STILL ANTICIPATED WHEN
SIMON EVENTUALLY MAKES LANDFALL IN THE LATTER PART OF THIS WEEK
BETWEEN 72-96 H.
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 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
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 12/2100Z 20.2N 106.8W 85 KT 100 MPH
12H 13/0600Z 20.5N 107.0W 75 KT 85 MPH
24H 13/1800Z 20.9N 107.5W 65 KT 75 MPH
36H 14/0600Z 21.2N 107.7W 70 KT 80 MPH
48H 14/1800Z 21.5N 107.7W 75 KT 85 MPH
60H 15/0600Z 22.2N 107.4W 80 KT 90 MPH
72H 15/1800Z 23.0N 107.0W 85 KT 100 MPH
96H 16/1800Z 24.2N 106.6W 30 KT 35 MPH...POST-TROP/INLAND
120H 17/1800Z...DISSIPATED
FORECASTER PAPIN
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