WDPN32 PGTW 030300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 06W (KHANUN) WARNING NR 028//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 26.6N 124.7E
   INITIAL INTENSITY: 90 KTS
   GEOGRAPHIC REFERENCE: 166 NM WEST OF KADENA AB
   MOVEMENT PAST 6 HOURS: WEST-NORTHWESTWARD AT 03 KTS
   SIGNIFICANT WAVE HEIGHT: 34 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) AND RADAR IMAGERY
FROM JAPAN INDICATE THAT THE INNER CORE OF TYPHOON 06W (KHANUN) HAS
BEGUN TO SIGNIFICANTLY DEGRADE DUE TO DYNAMIC OCEAN COOLING BENEATH
IT OWING TO ITS SLOW FORWARD CRAWL. THE INNER EYEWALL IS NOW FULLY
OPEN IN THE NORTHERN SEMICIRCLE, WITH THE STRONGEST RADAR ECHOES
NOW FOUND IN THE LARGER CONCENTRIC BAND ABOUT 100 NM IN DIAMETER.
MIYAKOJIMA IS REPORTING SUSTAINED WINDS OF 45 KT GUSTING TO 60 KT
IN THE SOUTHERN PERIPHERY OF THIS OUTER CORE BAND. PORTIONS OF
OKINAWA CONTINUE TO REPORT SUSTAINED WINDS JUST BELOW GALE FORCE,
BUT THE ISLAND IS NOW OUTSIDE OF THE TYPHOON'S CORE. THE INITIAL
INTENSITY IS LOWERED TO 90 KT BASED ON DECLINING DVORAK T-NUMBERS
AND OBJECTIVE SATELLITE ESTIMATES.

INITIAL WIND RADII BASIS: PERSISTENCE 

CURRENT STEERING MECHANISM: SUBTROPICAL RIDGE TO THE NORTH

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T5.0 - 90 KTS
   RJTD: T5.5 - 102 KTS
   RCTP: T5.0 - 90 KTS
   KNES: T5.5 - 102 KTS
   CIMSS ADT: 92 KTS AT 022330Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: UNFAVORABLE
   VWS: 10-15 KTS
   SST: 26-27 CELSIUS
   OUTFLOW: MODERATE RADIAL
   OTHER FACTORS: DYNAMIC OCEAN COOLING

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

3. FORECAST REASONING.

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

FORECAST DISCUSSION: TYPHOON 06W (KHANUN) HAS BEGUN THE DECAY
PROCESS ASSOCIATED WITH DYNAMIC OCEAN COOLING BENEATH THE CYCLONE
DUE TO ITS SLOW MOTION OVER THE EAST CHINA SEA. SUCH EVENTS
TYPICALLY RESULT IN RAPID WEAKENING OF THE INNER CORE AND A
BROADENING OF THE WIND FIELD STRUCTURE. IN KHANUN'S CASE, THIS IS
OCCURRING WHILE THE STORM HAS A DOUBLE-EYEWALL STRUCTURE, WHICH
MEANS THE INNER EYEWALL IS LIKELY TO DISINTEGRATE ENTIRELY, LEAVING
THE 100 NM WIDE OUTER CONCENTRIC BAND BEHIND. THIS OUTER BAND WILL
BECOME THE NEW BAND OF MAXIMUM WIND IN THE STORM, BUT THESE MAXIMUM
WINDS MAY FALL BELOW TYPHOON FORCE, WHICH THE JTWC INTENSITY
FORECAST SHOWS OCCURRING IN 48 HOURS. DUE TO THE COLD WATER,
KHANUN'S BROAD STRUCTURE MAY STRUGGLE TO CONTRACT FOR SEVERAL DAYS,
LIMITING ANY REINTENSIFICATION EVEN IF THE CYCLONE MOVES BACK OVER
WARMER WATERS. THE JTWC FORECAST SHOWS MILD RECOVERY TO 65 KT AT
96-120 HOURS. THE TRACK FORECAST IS MORE DIFFICULT, AS COMPETING
STEERING INFLUENCES WILL KEEP KHANUN MOVING AT A SLOW PACE DURING
THE ENTIRE FORECAST PERIOD, AND THERE IS A WIDE RANGE OF POSSIBLE
OUTCOMES. THE TRACK FORECAST IS CONFIDENT THROUGH 48 HOURS, AS
NUMERICAL MODELS ARE IN NEARLY UNANIMOUS AGREEMENT THAT KHANUN'S
WESTWARD MOTION WILL BE HALTED IN 12-24 HOURS BY INCREASING
MONSOONAL SOUTHWESTERLIES PUSHING ON THE TYPHOON, COMBINED WITH A
WEAKENING SUBTROPICAL RIDGE OVER KOREA. A TURN EAST-NORTHEASTWARD
BACK TOWARDS THE RYUKYU ISLANDS WILL ENSUE, WITH THE JTWC FORECAST
TRACK PASSING JUST SOUTH OF AMAMI OSHIMA BETWEEN 72 AND 96 HOURS.
AT THIS POINT, THE TYPHOON'S TRACK WILL BE DETERMINED BY SUBTLE
WAVES WITHIN THE JETSTREAM OVER KOREA, THE SUBTROPICAL RIDGE OVER
HONSHU, AND POTENTIAL BINARY INTERACTION WITH A NEW TROPICAL
CYCLONE POTENTIALLY FORMING SOUTHEAST OF HONSHU IN 3-5 DAYS. A
STRONGER JAPANESE RIDGE AND THE PRESENCE OF ANOTHER CYCLONE EAST OF
KHANUN, SUCH AS IN THE GFS MODEL, COULD BLUNT THE TYPHOON'S
EASTWARD MOVEMENT AND TURN IT NORTHWARD TOWARDS KYUSHU AND/OR
KOREA, POTENTIALLY STALLING AGAIN IN THE PROCESS. A WEAKER
SUBTROPICAL RIDGE, SUCH AS IN THE ECMWF MODEL, WOULD FAVOR A
CONTINUED EAST-NORTHEASTWARD TRACK TOWARDS HONSHU. THE TRUE OUTCOME
WILL HINGE STRONGLY ON WHETHER A SECOND CYCLONE DEVELOPS, A PROCESS
WHICH HAS NOT YET BEGUN, AND IS THEREFORE UNCERTAIN. THE JTWC
FORECAST CONTINUES TO STAY CLOSE TO THE MULTI-MODEL CONSENSUS,
THOUGH A TAD SLOWER AT 96-120 HOURS. KHANUN'S PROGRESS OVER THE
COMING DAYS WILL BARE WATCHING FOR THE ENTIRE REGION OF KOREA AND
JAPAN. REGARDLESS OF THE EXACT TRACK AND INTENSITY OF TYPHOON 06W,
A RATHER LARGE WIND FIELD IS EXPECTED TO PERSIST AND IMPACT A WIDE
AREA.

MODEL DISCUSSION: THE JTWC TRACK FORECAST IS CLOSE TO BUT SLIGHTLY
SLOWER THAN THE MULTI-MODEL CONSENSUS. THE JTWC INTENSITY FORECAST
IS SLIGHTLY LOWER THAN THE MULTI-MODEL CONSENSUS TO ACCOUNT FOR
MEMBERS OF THE CONSENSUS WHICH ARE NOT OCEAN-COUPLED AND ARE
THEREFORE LIKELY BIASED TOO STRONG.

FORECAST CONFIDENCE:
   TRACK 0 - 72 HR: MEDIUM
   TRACK 72-120 HR: LOW
   INTENSITY 0 - 72 HR: MEDIUM
   INTENSITY 72-120 HR: MEDIUM//
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