WPAC: MUN - Post-Tropical - Discussion

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SUMMARY:
INITIAL POSITION: 27.6N 145.4E
INITIAL INTENSITY: 50 KTS
GEOGRAPHIC REFERENCE: 173 NM EAST OF CHICHI JIMA
MOVEMENT PAST 6 HOURS: NORTHWARD AT 06 KTS
SIGNIFICANT WAVE HEIGHT: 20 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
TROPICAL STORM (TS) 04W HAS MAINTAINED A COMPLEX UPPER-LEVEL OUTFLOW
PATTERN, WITH AN UPPER-LEVEL CYCLONE POSITIONED OVER THE CENTER AND
STRONG EASTWARD, DIFFLUENT OUTFLOW ENHANCED BY A JET TO THE NORTHEAST.
THE PRESENCE OF THE UPPER-LEVEL LOW AND DRY AIR ENTRAINMENT WITHIN THE
CORE OF THE SYSTEM IS HINDERING CONVECTIVE DEVELOPMENT. DESPITE THIS
LIMITATION, ANIMATED MULTISPECTRAL SATELLITE IMAGERY DEPICTS TIGHTLY
WRAPPED LOW-LEVEL BANDING AND A WELL-DEFINED LOW-LEVEL CIRCULATION
CENTER SUPPORTING THE INITIAL POSITION WITH HIGH CONFIDENCE. THE
INITIAL INTENSITY IS ASSESSED AT 50 KNOTS BASED ON THE PGTW AND KNES
DVORAK ESTIMATES, WHICH ARE CONSISTENT WITH RECENT ASCAT UHR DATA
SHOWING A PATCH OF 50-55 KNOT WINDS. CIMSS OBJECTIVE ESTIMATES REMAIN
TOO LOW, RANGING FROM 33-39 KNOTS. AS INDICATED IN THE DYNAMIC MODELS,
THE CORE IS EXPECTED TO MOISTEN AND CONSOLIDATE WITHIN THE NEXT 12
HOURS, WHICH IS EXPECTED TO LEAD TO A SHARPER INTENSIFICATION RATE.
OVER THE PAST FEW HOURS, THERE APPEARS TO BE SOME EVIDENCE THAT THIS
IS COMMENCING, WITH ANIMATED INFRARED SATELLITE IMAGERY REVEALING
BETTER ORGANIZED CORE CONVECTION, WITH CLOUD TOP TEMPERATURES NEAR
-59C.

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Up to 60kt and will be a Typhoon later today.

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21:00 UTC:

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04W MUN 250704 0000 29.6N 144.8E WPAC 55 982

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FORECAST DISCUSSION: TROPICAL STORM (TS) 04W (MUN) IS TRAVELING
ALMOST DUE NORTH, ALONG THE WESTERN SIDE OF THE STEERING RIDGE.
HOWEVER, THE NORTHERN EXTENSION OF THIS STEERING RIDGE IS RAPIDLY
WEAKENING, IN FAVOR OF A BUILDING RIDGE OVER THE CENTRAL MARIANAS.
OVER THE COURSE OF THE NEXT 12 HOURS, TS 04W WILL GRADUALLY TURN
TOWARDS THE EAST-NORTHEAST, DRIVEN ALONG THE NORTHERN SIDE OF THE
BUILDING RIDGE TO THE SOUTH. AFTER TAU 48, THE STR TO THE SOUTH
MOVES WESTWARD WHILE A DEEP-LAYER BUBBLE HIGH DEVELOPS EAST OF TS
04W, DRIVING THE SYSTEM POLEWARD FROM TAU 48 TO TAU 96. AFTER TAU
96, THE SYSTEM WILL TRACK INTO A BREAK IN THE RIDGE AND BE CAUGHT
UP IN THE MID-LATITUDE WESTERLIES AND QUICKLY TURN TO THE
NORTHEAST. IN TERMS OF INTENSITY, AS SEEN IN THE MOST RECENT MSI
AND IR LOOPS, THE VORTEX MAY BE TRYING TO REALIGN AT THE MOMENT. AS
THIS PROCESS COMPLETES AND POLEWARD OUTFLOW IMPROVES, THERE SHOULD
BE ENOUGH WARM WATER LEFT TO SUPPORT A SLOW BUT STEADY
INTENSIFICATION OVER THE NEXT 36 HOURS. AROUND TAU 60, A STRONG
MID-LATITUDE TROF AND DEFORMATION ZONE WILL MOVE IN FROM THE
NORTHWEST, USHERING IN A SHARP INCREASE IN SHEAR AND DRY MID-LEVEL
AIR, EFFECTIVELY DECAPITATING AND SMOTHERING TS 04W. THIS WILL MARK
THE ONSET OF BOTH SUBTROPICAL TRANSITION (STT) AND A RAPID
WEAKENING TREND, WHICH WILL CONTINUE THROUGH THE REMAINDER OF THE
FORECAST PERIOD.

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SIGNIFICANT FORECAST CHANGES: THERE ARE NO SIGNIFICANT CHANGES TO
THE FORECAST FROM THE PREVIOUS WARNING.

FORECAST DISCUSSION: TS 04W IS EMBEDDED WITHIN A REVERSE TROUGH
FORMATION, WITH THE SUBTROPICAL STEERING RIDGE EXTENDING FROM THE
PHILIPPINES NORTHEASTWARD TO THE EASTERN PERIPHERY OF THE SYSTEM.
THIS IS GENERAL STEERING PATTERN WILL STEER THE SYSTEM NORTHEASTWARD
THROUGH TAU 36 TOWARD A BREAK IN THE STR ASSOCIATED WITH AN UPPER-
LEVEL SHORTWAVE TROUGH. MODEST INTENSIFICATION IS EXPECTED DUE TO
MARGINAL SST VALUES (24-25C) AND ROBUST OUTFLOW, WITH A PEAK INTENSITY
OF 70 KNOTS EXPECTED BY TAU 24. AFTER TAU 36, THE TROUGH WILL
PROPAGATE EASTWARD AND THE STR WILL REBUILD TO THE NORTH, WHICH WILL
RESULT IN A MORE NORTHWARD TRACK THROUGH TAU 96. AFTER TAU 96, THE
SYSTEM WILL ROUND THE STR AXIS AND ENCOUNTER SUBTROPICAL WESTERLIES.
RAPID WEAKENING WILL OCCUR THROUGH THE REMAINDER OF THE PERIOD DUE TO
COLD SST VALUES AND HIGH (25-40 KNOTS) VERTICAL WIND SHEAR.

MODEL DISCUSSION: DETERMINISTIC MODEL GUIDANCE IS IN GOOD AGREEMENT
THROUGH TAU 36 BUT DIVERGES QUICKLY THROUGH TAU 120. WITH THE
EXCEPTION OF NAVGEM, THE SOLE OUTLIER, THE DETERMINISTIC MODELS
HAVE COME INTO BETTER AGREEMENT, WITH GFS NOW SHIFTING SIGNIFICANTLY
CLOSER TO THE BULK OF THE GUIDANCE. THE 040600Z GEFS ENSEMBLE
CONTINUES TO INDICATE A WIDE SPREAD OF SOLUTIONS, WITH THE BULK OF THE
GUIDANCE WELL EAST OF JAPAN. THE ECENS ENSEMBLE REMAINS IN TIGHTER
AGREEMENT AND SUPPORTS THE JTWC TRACK FORECAST WITH MEDIUM OVERALL
CONFIDENCE. RELIABLE INTENSITY GUIDANCE INDICATES A PEAK INTENSITY
NEAR TAU 24 BUT VARIES SIGNIFICANTLY FROM 58 TO 76 KNOTS. THIS
REFLECTS THE UNCERTAINTY IN THE JTWC INTENSITY FORECAST, WITH MEDIUM
OVERALL CONFIDENCE.

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Getting better organized.

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 https://x.com/WillWeatherRVA/status/1941890360273146000