Advisories

WDPN32 PGTW 210900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR SUPER TYPHOON 29W (CHAMPI) WARNING NR 
028//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 18.7N 128.9E
   INITIAL INTENSITY: 150 KTS
   GEOGRAPHIC REFERENCE: 472 NM SOUTH OF KADENA AB
   MOVEMENT PAST 6 HOURS: WEST-NORTHWESTWARD AT 13 KTS
   SIGNIFICANT WAVE HEIGHT: 65 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
SUPER TYPHOON (STY) 29W MAINTAINS THE CLASSIC APPEARANCE OF A
LARGE, VERY POWERFUL TROPICAL CYCLONE. A CLEAR, 30-NM-WIDE EYE IS
EMBEDDED IN A SYMMETRIC CENTRAL DENSE OVERCAST (CDO) WITH EXTENSIVE
SPIRAL BANDS ALONG THE OUTER PERIPHERY AND EXCELLENT VENTILATION.
WHILE ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS THE
CDO WITH A SMOOTH CANOPY, CLOUD-TOP TEMPERATURES HAVE GRADUALLY
WARMED. THE EYE REMAINS WARM AT +22 DEGREES CELSIUS. PERSISTENT,
FAR-REACHING CONVECTIVE BANDS ARE ASSOCIATED WITH AN EXPANSION OF
THE GALE-FORCE WIND RADII, AS REVEALED BY A 210032Z ASCAT-B PASS.
THE ENVIRONMENT REMAINS FAVORABLE WITH LOW VERTICAL WIND SHEAR
(VWS). HOWEVER, THE SYSTEM HAS MOVED OVER COOLER SEA SURFACE
TEMPERATURES (SST) OF 27-28 DEGREES CELSIUS AND OCEAN HEAT CONTENT
(OHC) OF 50-70 KJ PER CM2, WHICH IS LESS SUPPORTIVE OF MAINTAINING
SUPER TYPHOON INTENSITY. THE INITIAL POSITION IS PLACED WITH HIGH
CONFIDENCE BASED ON THE WELL-DEFINED EYE IN MSI. THE INITIAL
INTENSITY HAS BEEN LOWERED TO 150 KTS WITH MEDIUM CONFIDENCE,
SUPPORTED BY THE DECREASING FINAL T-NUMBERS FROM PGTW, RJTD, AND
RCTP AND DECREASING OBJECTIVE INTENSITY ESTIMATES FROM CIMSS.

INITIAL WIND RADII BASIS: SCATTEROMETER DATA 

CURRENT STEERING MECHANISM: SOUTHWESTERN FLANK OF A DEEP-LAYER
SUBTROPICAL RIDGE (STR) CENTERED SOUTHEAST OF HONSHU

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T7.5 - 155 KTS
   RJTD: T7.5 - 155 KTS
   RCTP: T7.5 - 155 KTS
   CIMSS SATCON: 144 KTS AT 210455Z
   CIMSS ADT: 124 KTS AT 210530Z
   CIMSS AIDT: 141 KTS AT 210530Z
   CIMSS D-MINT: 148 KTS AT 210456Z
   CIMSS D-PRINT: 149 KTS AT 210640Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 0-5 KTS
   SST: 27-28 CELSIUS
   OUTFLOW: STRONG RADIAL

ANALYSIS CONFIDENCE:
   INITIAL POSITION: HIGH
   INITIAL INTENSITY: MEDIUM
   INITIAL WIND RADII: HIGH

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: THE JTWC FORECAST TRACK HAS SHIFTED
WESTWARD BY 25 NM FROM TAU 48 THROUGH TAU 72.

FORECAST DISCUSSION: STY 29W WILL CONTINUE ON A NORTHWESTWARD
TRAJECTORY THROUGH TAU 36 AS A SHARP MID-LEVEL TROUGH APPROACHING
HONSHU CREATES A WEAKNESS IN THE STR. THIS WEAKNESS WILL ALLOW THE
SYSTEM TO TURN POLEWARD AND GAIN LATITUDE MORE QUICKLY. THEREAFTER,
TWO DIVERGENT TRACK SCENARIOS REMAIN POSSIBLE. THE DYNAMICAL MODELS
PREDICT THAT THE STR WILL QUICKLY BUILD WESTWARD, WHICH WOULD KEEP
STY 29W ON A NORTHWESTWARD TRACK INTO TAIWAN. THE AI MODELS BUILD
THE RIDGE LESS QUICKLY, WHICH WOULD CAUSE THE SYSTEM TO CONTINUE
POLEWARD, CROSS THE RIDGE AXIS, AND ACCELERATE NORTHEASTWARD. WHILE
VWS WILL REMAIN LOW AS THE SYSTEM APPROACHES TAIWAN, THE LOWER OHC
AND COOLER SSTS AHEAD WILL BE INSUFFICIENT TO SUSTAIN THE CURRENT
HIGH INTENSITY OF STY 29W, LEADING TO STEADY TO RAPID WEAKENING IN
THE IMMEDIATE TERM. IF THE DYNAMICAL SOLUTIONS COME TO FRUITION,
SIGNIFICANT WEAKENING DUE TO LAND INTERACTION WILL OCCUR AT
LANDFALL OVER TAIWAN AND CONTINUE ACROSS THE TAIWAN STRAIT AND
THROUGH A SECOND LANDFALL OVER CENTRAL CHINA. UNDER THE RECURVATURE
SCENARIO, VWS WILL REMAIN LOW THROUGH TAU 72, AND A PATCH OF HIGHER
OHC FROM TAU 36 TO JUST AFTER TAU 48 WILL BRIEFLY LIMIT THE RATE OF
WEAKENING. AFTER THE SYSTEM LEAVES THIS PATCH, COOLER SST AND LOWER
OHC WILL SUPPORT A SECOND PERIOD OF MORE RAPID WEAKENING FROM TAU
48 THROUGH TAU 72. DEEP-LAYER SHEAR WILL QUICKLY INCREASE AT TAU 96
AND TAU 120 AS THE STORM MOVES BENEATH THE SOUTHERN PERIPHERY OF AN
UPPER-LEVEL JET. THE INCREASINGLY BAROCLINIC ENVIRONMENT MAY SLOW
THE RATE OF WEAKENING AS EXTRATROPICAL TRANSITION BEGINS BY TAU
120.

MODEL DISCUSSION: TRACK GUIDANCE IS IN GOOD AGREEMENT THROUGH TAU
24 AND BEGINS TO SPLIT THEREAFTER, WITH PHYSICS-BASED MODELS STILL
SHOWING A LANDFALL OVER CENTRAL TO NORTHERN TAIWAN AND AI MODELS
RECURVING THE SYSTEM INTO OR JUST NORTH OF KYUSHU. ONLY HAFS-A
DEPICTS A WESTWARD TRACK INTO SOUTHERN TAIWAN AND SOUTHEAST CHINA.
FROM TAU 60 TO TAU 96, THE PHYSICS-BASED MODELS HAVE SHIFTED
SLIGHTLY EASTWARD, WHILE THE AI MODELS HAVE SHIFTED SLIGHTLY
WESTWARD. REFLECTING THIS TREND, THE JTWC FORECAST TRACK HAS BEEN
NUDGED SLIGHTLY WESTWARD WHILE REMAINING CLOSE TO THE AI-MODEL MEAN
THROUGH TAU 96. AT TAU 120, THE FORECAST POINT IS POSITIONED
BETWEEN THE MORE POLEWARD AIFS AND THE MORE EQUATORWARD GOOGLE
DEEPMIND AND AI-MODEL MEAN. IF THESE TRENDS CONTINUE, SUBSEQUENT
FORECASTS MAY NEED TO SHIFT THE TRACK FARTHER WEST, INCREASING THE
CPA DISTANCE TO OKINAWA AND DELAYING THE APPROACH TO KYUSHU.
FURTHERMORE, A MORE WESTWARD TRACK WOULD KEEP THE SYSTEM OVER
COOLER WATERS AND HIGHER SHEAR FOR A LONGER PERIOD, RESULTING IN
MORE WEAKENING PRIOR TO ITS FINAL APPROACH TO KYUSHU. IN FACT,
THERE IS A NON-ZERO CHANCE THAT THE STORM WEAKENS BELOW STORM-FORCE
INTENSITY, POTENTIALLY TO MINIMAL TROPICAL-STORM STRENGTH, AS IT
APPROACHES MAINLAND JAPAN IF WESTWARD ADJUSTMENTS CONTINUE. BASED
ON THE JTWC TRACK, THE INTENSITY FORECAST IS SET NEAR THE INTENSITY
CONSENSUS AND THE GOOGLE DEEPMIND SOLUTION. THESE SOLUTIONS DEPICT
RAPID WEAKENING THROUGH TAU 36, A BRIEFLY SLOWER RATE FROM TAU 36
TO TAU 48, AND A SECOND PERIOD OF RAPID WEAKENING FROM TAU 48 TO
TAU 72. BECAUSE OF THESE DIVERGENT SCENARIOS, THE TIMING AND
LOCATION OF THE CLOSEST APPROACH TO KYUSHU MAY CHANGE SIGNIFICANTLY
AS GUIDANCE CONVERGES TOWARD A CLEARER SOLUTION.

FORECAST CONFIDENCE:
   TRACK 00-72 HR: LOW
   TRACK 72-120 HR: LOW
   INTENSITY 00-72 HR: LOW
   INTENSITY 72-120 HR: LOW//
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