Advisories

WDPN32 PGTW 211500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR SUPER TYPHOON 29W (CHAMPI) WARNING NR 
029//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 19.3N 127.9E
   INITIAL INTENSITY: 145 KTS
   GEOGRAPHIC REFERENCE: 432 NM SOUTH OF KADENA AB
   MOVEMENT PAST 6 HOURS: NORTHWESTWARD AT 11 KTS
   SIGNIFICANT WAVE HEIGHT: 60 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
SUPER TYPHOON (STY) 29W MAINTAINS A VERY IMPRESSIVE APPEARANCE IN
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY, FEATURING A
30-NM-WIDE EYE EMBEDDED IN A SYMMETRIC CENTRAL DENSE OVERCAST WITH
EXTENSIVE BANDING FEATURES AND EXCELLENT UPPER-LEVEL OUTFLOW. CLOUD
TOP TEMPERATURES GRADUALLY WARMED OVER THE PAST 18 HOURS BUT HAVE
SINCE REVERSED COURSE. IN BD-CURVE-ENHANCED IMAGERY, A RING OF
WHITE AND COLD-MEDIUM-GRAY SHADES HAS ENCIRCLED THE EYE. THIS
FOLLOWS SSMIS MICROWAVE PASSES AT 210922Z AND 211003Z, WHICH
REVEALED CONCENTRIC CONVECTIVE RINGS AND INDICATED THE POTENTIAL
FOR AN EYEWALL REPLACEMENT CYCLE (ERC). IT IS DIFFICULT TO
DETERMINE WHETHER THE RECENT CLOUD-TOP COOLING IS ASSOCIATED WITH
THE INNER EYEWALL OR THE OUTER RING. THUS FAR, THE EYE HAS SHOWN NO
INDICATION OF DISRUPTION, REMAINING CLEAR, CIRCULAR, AND AS WARM AS
+20 DEGREES CELSIUS. THE ENVIRONMENT REMAINS FAVORABLE WITH LOW
VERTICAL WIND SHEAR (VWS). HOWEVER, THE SYSTEM IS TRAVERSING 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 EIR IMAGERY.
THE INITIAL INTENSITY HAS BEEN LOWERED TO 145 KTS WITH MEDIUM
CONFIDENCE BASED ON A BLEND OF THE OBJECTIVE ESTIMATES FROM CIMSS.
ADT IS DISCOUNTED AS BEING TOO LOW BECAUSE ITS EARLIER PEAK WAS
CONSTRAINED BY THE LARGE-EYE SCENE TYPE.

INITIAL WIND RADII BASIS: PERSISTENCE 

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

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T7.5 - 155 KTS
   RJTD: T7.5 - 155 KTS
   RCTP: T7.0 - 140 KTS 
   CIMSS SATCON: 150 KTS AT 211200Z
   CIMSS ADT: 117 KTS AT 211200Z
   CIMSS AIDT: 141 KTS AT 211200Z
   CIMSS D-MINT: 148 KTS AT 211004Z
   CIMSS D-PRINT: 138 KTS AT 211200Z

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: MEDIUM

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: THE CPA TO KYUSHU HAS BEEN DELAYED BY
APPROXIMATELY 4 HOURS.

FORECAST DISCUSSION: STY 29W WILL CONTINUE NORTHWESTWARD ALONG THE
SOUTHWESTERN PERIPHERY OF A DEEP-LAYER STR THROUGH TAU 24. DURING
THIS TIME, VWS WILL REMAIN LOW, BUT COOLER SST AND LOW OHC WILL
PROMOTE RAPID WEAKENING. THE CIRCULATION IS ALSO VERY LARGE, WITH
GALE-FORCE WINDS EXTENDING FAR FROM THE CENTER. CURRENTLY, THE
SYSTEM IS MOVING TOWARD A WEAKNESS IN THE STR CAUSED BY A DEEP
TROUGH PASSING OVER HONSHU. THE STR WILL REBUILD WESTWARD OVER THE
NEXT 48-72 HOURS. UNCERTAINTY ASSOCIATED WITH THE EVOLUTION OF THIS
RIDGE LEADS TO A RANGE OF POSSIBILITIES, FROM LANDFALL OVER
NORTHERN TAIWAN TO RECURVATURE TOWARD KYUSHU.

UNDER THE TAIWAN SCENARIO, THE STR WOULD REBUILD QUICKLY AND
PREVENT STY 29W FROM GAINING SIGNIFICANT LATITUDE. THE SYSTEM WOULD
THEN MAKE LANDFALL OVER NORTHERN TAIWAN BETWEEN TAU 48 AND TAU 60,
WEAKEN SIGNIFICANTLY OVER LAND, EMERGE OVER THE TAIWAN STRAIT AS A
TROPICAL STORM, AND MAKE A SECOND LANDFALL OVER CENTRAL CHINA NEAR
TAU 96. ON THE OTHER SIDE OF THE SPECTRUM, THE RIDGE WOULD BUILD
LATER OR MORE SLOWLY, ALLOWING STY 29W TO TURN POLEWARD AND
NORTHEASTWARD BEFORE MAKING LANDFALL OVER KYUSHU. THIS TRACK WOULD
BRING THE SYSTEM OVER A POOL OF HIGHER OHC BETWEEN TAU 24 AND TAU
48, BRIEFLY SLOWING THE RATE OF WEAKENING. THEREAFTER, THE SYSTEM
WOULD QUICKLY WEAKEN AS IT ENCOUNTERS MUCH LOWER SST AND HIGHER VWS
ASSOCIATED WITH THE SOUTHERN PERIPHERY OF THE JET STREAM,
POTENTIALLY MAKING LANDFALL OVER KYUSHU AFTER TAU 96 AS A TROPICAL
STORM.

SOLUTIONS BETWEEN THESE TWO ENDS OF THE SPECTRUM ARE ALSO POSSIBLE.
STY 29W COULD MAKE A CLOSE APPROACH TO TAIWAN, THEN SPEND MORE TIME
OVER THE COOLER WATERS OF THE EAST CHINA SEA AS IT RECURVES ALONG A
WIDER TURN, AND APPROACH KYUSHU OR THE SOUTHERN PERIPHERY OF THE
REPUBLIC OF KOREA AS A WEAK TROPICAL STORM OR TROPICAL DEPRESSION.
UNDER THESE RECURVATURE SCENARIOS, THE SYSTEM WOULD UNDERGO
EXTRATROPICAL TRANSITION (ETT) AS EARLY AS TAU 96 AND POTENTIALLY
COMPLETE ETT BY TAU 120. THE JTWC FORECAST TRACK, WHICH HAD BEEN
FAVORING THE RECURVATURE SCENARIO, CONTINUES TO LEAN TOWARD
RECURVATURE.

MODEL DISCUSSION: A BIFURCATION IN TRACK GUIDANCE REMAINS, WITH
DYNAMICAL MODELS CONTINUING TO FAVOR A LANDFALL OVER TAIWAN OR A
TRACK JUST EAST OF TAIWAN. AI MODELS PREFER THE RECURVATURE
SCENARIO. THIS CYCLE, THE BULK OF THE DYNAMICAL SOLUTIONS HAS
SHIFTED EASTWARD AFTER TAU 24, WITH ONLY A FEW MEMBERS NOW SHOWING
A LANDFALL OVER CENTRAL TAIWAN. GFS AND ECMWF DEPICT THE SYSTEM
CLIPPING THE NORTHEASTERN TIP OF TAIWAN AS IT RECURVES WIDELY, THEN
MAKING A SECOND LANDFALL OVER ZHEJIANG PROVINCE. NAVGEM KEEPS THE
SYSTEM ENTIRELY OFFSHORE ALONG A WIDE TURN BEFORE DEPICTING
LANDFALL OVER KYUSHU. THE JTWC FORECAST TRACK IS VIRTUALLY
UNCHANGED THROUGH TAU 96 FROM THE PREVIOUS FORECAST. IT IS WELL
ALIGNED WITH GOOGLE DEEPMIND AND IS SLIGHTLY EAST OF THE AI-MODEL
MEAN THROUGH TAU 96. THE TAU 120 FORECAST POINT HAS BEEN SHIFTED
SOUTHWARD AND IS NEAR THE MIDPOINT BETWEEN AIFS AND DEEPMIND. THE
FORECAST MOTION HAS BEEN SLOWED TO REFLECT A SHALLOWER SYSTEM NEAR
KYUSHU STEERED BY WEAKER LOWER-LEVEL FLOW.

THE INTENSITY GUIDANCE SUITE DEPICTS A GENERAL WEAKENING TREND
THROUGHOUT THE FORECAST PERIOD. GFS AND COAMPS-TC, WHICH TRACK THE
SYSTEM OVER TAIWAN, DEPICT A SHARPER RATE OF WEAKENING DUE TO
LANDFALL OVER TAIWAN. THESE SOLUTIONS WERE DISCOUNTED FOR THIS
FORECAST. THE JTWC INTENSITY FORECAST LEANS TOWARD THE DEEPMIND
SOLUTION, SHOWING RAPID WEAKENING FOR THE FIRST 24 HOURS, FOLLOWED
BY A SLOWER RATE OF WEAKENING FROM TAU 24 TO TAU 48, AND A SECOND
ROUND OF RAPID WEAKENING FROM TAU 48 TO TAU 72. THE WEAKENING TREND
SLOWS AFTER TAU 72 AS THE SYSTEM ENTERS THE BAROCLINIC ZONE AND
UNDERGOES ETT.

CONFIDENCE IS LOW IN THE EVENTUAL TRACK OF STY 29W, AND SUBSTANTIAL
UNCERTAINTY EXISTS IN THE TRANSLATION SPEED UNDER A RECURVATURE
SCENARIO. THE AI MODELS EXHIBIT LARGE ALONG-TRACK SPREAD THAT
DEPENDS ON THE SHARPNESS OF THE RECURVE AND THE SYSTEM INTENSITY ON
FINAL APPROACH TO KYUSHU. BECAUSE INTENSITY AFTER TAU 24 WILL BE
HIGHLY DEPENDENT ON THE TRACK, CONFIDENCE IN THE INTENSITY IS ALSO
LOW. SIGNIFICANT CHANGES MAY OCCUR IN SUBSEQUENT FORECASTS TO THE
TIMING AND LOCATION OF THE CPA TO KYUSHU AND TO THE INTENSITY OF
THE SYSTEM AFTER RECURVATURE AS GUIDANCE SLOWLY 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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