WDPN32 PGTW 012100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 06W (KHANUN) WARNING NR 023//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 25.6N 127.4E
   INITIAL INTENSITY: 110 KTS
   GEOGRAPHIC REFERENCE: 53 NM SOUTH-SOUTHWEST OF KADENA AB
   MOVEMENT PAST 6 HOURS: WEST-NORTHWESTWARD AT 06 KTS
   SIGNIFICANT WAVE HEIGHT: 41 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
TYPHOON (TY) 06W (KHANUN) HAS MADE ITS CLOSEST POINT OF APPROACH TO
OKINAWA AT THE 1800Z HOUR, ROUGHLY 53NM SOUTH-SOUTHWEST OF KADENA
AB, AND APPROXIMATELY 30NM SOUTH-SOUTHWEST OF THE SOUTHERN TIP OF
THE ISLAND. BASED ON ANALYSIS OF JMA RADAR DATA SHOWS THE OUTER
EDGES OF THE INNER-CORE SKIRTING THE SOUTHERN SIDE OF THE ISLAND
WITH STRONG RAIN BANDS CROSSING OVER OKINAWA ITSELF, BRINGING
SUSTAINED STORM TO TYPHOON STRENGTH WINDS AND TYPHOON STRENGTH
GUSTS ACROSS THE ISLAND. ANIMATED ENHANCED INFRARED (EIR) SATELLITE
IMAGERY DEPICTS A 17NM WIDE EYE, WHICH IS BECOMING INCREASINGLY
RAGGED AND DISORGANIZED AS IT PASSES OKINAWA. THE RADAR DATA AND A
011924Z SSMIS 89GHZ IMAGE SHOW DEVELOPMENT OF A SECONDARY EYEWALL
THAT SURROUNDS ALL BUT THE SOUTHWEST QUADRANT OF THE INNER CORE,
SUPPORTING THE ASSESSMENT THAT THE SYSTEM IS ABOUT MIDWAY THROUGH
AN EYEWALL REPLACEMENT CYCLE (EWRC). THE INITIAL INTENSITY OF 110
KNOTS IS ASSESSED WITH MEDIUM CONFIDENCE, HEDGED SLIGHTLY LOWER
THAN THE MAJORITY OF AGENCY DVORAK CURRENT INTENSITY ESTIMATES AS
WELL AS THE SUBJECTIVE ESTIMATES WHICH ARE ALL AT OR ABOVE 114
KNOTS. THE HEDGE BELOW IS DUE TO THE IMPACTS OF THE EWRC, THE
SLOWLY DEGRADING STRUCTURE IN THE EIR AND AS A NOD TOWARDS A SAR
PASS FROM 010900Z WHICH INDICATED WINDS OF JUST 87 KNOTS, WHICH
INTRODUCES A LARGE HELPING OF UNCERTAINTY IN THE INITIAL INTENSITY
ASSESSMENT. UNFORTUNATELY, THE KADENA AB NEXRAD IS DOWN, PRECLUDING
MEASUREMENT OF RADAR VELOCITY DATA AS THE SYSTEM PASSES CLOSE
ABOARD. ENVIRONMENTAL CONDITIONS REMAIN GENERALLY FAVORABLE WITH
WARM SSTS, GOOD POLEWARD OUTFLOW INTO A TUTT-CELL SOUTH OF TOKYO 
AND LOW NORTHERLY WIND SHEAR. THE DRY UPPER-LEVEL AIR PRESENT TO
THE NORTH OF THE SYSTEM YESTERDAY HAS SLID DOWN THE WESTERN EDGE OF
THE SYSTEM, CAUSING SOME MINOR EROSION OF THE EYEWALL ON THE
WESTERN SIDE OF THE CORE.

INITIAL WIND RADII BASIS: PERSISTENCE 

CURRENT STEERING MECHANISM: SOUTHERN PERIPHERY OF A DEEP-LAYER
SUBTROPICAL RIDGE (STR) CENTERED OVER THE YELLOW SEA. 

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T6.0 - 115 KTS
   RJTD: T6.0 - 115 KTS
   RCTP: T6.0 - 115 KTS
   KNES: T6.0 - 115 KTS
   CIMSS SATCON: 127 KTS AT 011730Z
   CIMSS ADT: 119 KTS AT 011730Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 10-15 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: STRONG POLEWARD
   OTHER FACTORS: UPPER-LEVEL DRY AIR ON THE WESTERN PERIPHERY OF
THE SYSTEM. 

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

3. FORECAST REASONING.

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

FORECAST DISCUSSION: OVER THE NEXT 48 HOURS, TY 06W WILL CONTINUE
TO TRACK TOWARDS THE WEST-NORTHWEST ALONG THE SOUTHERN SIDE OF THE
DEEP STR ENTRENCHED TO THE NORTH. THE RIDGE CENTER IS FORECAST TO
SLIDE TOWARDS THE SOUTHEAST DURING THIS TIMEFRAME, TO A POSITION
OVER THE SHANDONG PROVINCE OF CHINA WHICH WILL SERVE TO SLOW AND
THEN STOP THE WESTWARD PROGRESS OF TY 06W. THE CURRENT FORECAST
CALLS FOR THE SYSTEM TO BECOME QUASI-STATIONARY BY TAU 36,
REMAINING EAST OF THE 124E LONGITUDE LINE. THE PRIMARY STEERING
INFLUENCE IS FORECAST TO SHIFT OVER TO THE NEAR EQUATORIAL RIDGE
(NER) TO THE SOUTHEAST BY TAU 48, WHICH WILL EJECT TY 06W ONTO A
GRADUALLY ACCELERATING EAST-NORTHEASTWARD TRACK AFTER TAU 48. THE
SYSTEM WILL TAKE SOME TIME TO PICK UP SPEED AND TRACK MOTION WILL
BE VERY SLOW AND ERRATIC UNTIL ABOUT TAU 72 WHEN THE TRACK SPEEDS
BEGIN TO EXCEED 5 KNOTS AS THE NER BUILDS AND THE STEERING GRADIENT
TIGHTENS UP. IN TERMS OF INTENSITY, THE SYSTEM IS FORECAST TO
SLOWLY WEAKEN THROUGH THE FIRST 36 HOURS DUE TO THE COMBINED
EFFECTS OF THE EWRC, A GRADUAL REDUCTION IN UPPER-LEVEL OUTFLOW AND
AN INCREASE IN VERTICAL WIND SHEAR, PARTICULARLY IN THE MIDDLE
LAYERS OF THE ATMOSPHERE. AFTER TAU 36 ONCE THE SYSTEM BECOMES
QUASI-STATIONARY, RAPID AND INTENSE UPWELLING WILL LEAD TO
SIGNIFICANT SST COOLING, WHICH COMBINED WITH AN ENLARGED WIND FIELD,
THE RESULT OF THE EWRC, THE SYSTEM WILL RAPIDLY WEAKEN TO 55 KNOTS
BY TAU 96. BY TAU 120, THE SYSTEM MOVES AWAY FROM THE UPWELLING
REGION, AND INTO A SLIGHTLY IMPROVED UPPER-LEVEL ENVIRONMENT, AND
WILL MAINTAIN INTENSITY THROUGH THE END OF THE FORECAST. 

MODEL DISCUSSION: DETERMINISTIC AND ENSEMBLE TRACK GUIDANCE, WHILE
IN GENERAL CONSISTENT WITH EARLIER RUNS, ARE BEGINNING TO SHOW
INCREASING DIVERGENCE IN THE LATER HALF OF THE FORECAST PERIOD. THE
HAFS-A AND HWRF TAKE THE SYSTEM A BIT MORE TO THE SOUTH THAN THE
BULK OF THE GUIDANCE, WHILE THE EGRR GOES A BIT FURTHER NORTH AND
WEST BUT OVERALL, THE COMPLETE PACKAGE CONSTRAINED TO AN 85NM
CIRCLE AT TAU 48. BY TAU 72, THINGS START TO GET INTERESTING...ALL
OF THE AVAILABLE GUIDANCE, EVEN INCLUDING THE EGRR AND UKMET
ENSEMBLE WHICH NOW GIVE UP ON THEIR TRACK TO CHINA, SHARPLY TURN
THE SYSTEM TO THE NORTHEAST BY TAU 72 INTO A 150NM ENVELOPE WITH
THE HWRF MARKING THE FURTHEST EAST AND SOUTH (ALMOST OVER OKINAWA
AGAIN) AND THE UKMET MODELS THE FURTHEST WEST AND NORTH. THE
CONSENSUS MEMBERS DIVERGE IN BOTH CROSS AND ALONG-TRACK SPREAD
RAPIDLY AFTER TAU 96, SUCH THAT BY TAU 120 THE CROSS-TRACK ENVELOPE
EXTENDS FROM THE UKMET IN THE EAST CHINA SEA TO THE ECMWF SOUTH OF
KYOTO, AND THE GFS AND HWRF EAST OF OKINAWA, OR IN OTHER WORDS
ROUGHLY A 500NM BY 225NM BOX OF UNCERTAINTY. THE JTWC FORECAST IS
HEDGED OVER A BIT TOWARDS THE ECMWF AND GFS SOLUTIONS, AND LIES
ABOUT 20NM SOUTH OF THE CONSENSUS MEAN. CONFIDENCE THROUGH TAU 48
IS HIGH, BUT RAPIDLY TRANSITIONS TO LOW AFTER THIS POINT. INTENSITY
GUIDANCE IS IN GOOD AGREEMENT THROUGH TAU 48 BUT THEN WIDENS UP TO
A 35 KNOT ENVELOPE AFTERWARDS AS THE MODELS DISAGREE ON THE AMOUNT
OF WEAKENING THAT WILL OCCUR DUE TO THE UPWELLING. 

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