WDPN31 PGTW 261500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR SUPER TYPHOON 20W (MINDULLE) WARNING 
NR 017//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 19.0N 136.7E
   INITIAL INTENSITY: 130 KTS
   GEOGRAPHIC REFERENCE: 432 NM SOUTHWEST OF IWO TO
   MOVEMENT PAST 6 HOURS: NORTHWARD AT 02 KTS
   SIGNIFICANT WAVE HEIGHT: 48 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS A
SIGNIFICANTLY DEGRADED APPEARANCE, WITH AN INCREASINGLY RAGGED 20-NM
EYE, COOLING EYE TEMPERATURES AND A VAST REDUCTION IN THE WARMING
CONVECTIVE CORE. THE SYSTEM IS ALSO EXHIBITING SOME DEGRADATION OF
THE EYEWALL ON THE NORTHWEST SIDE, WITH ONLY A VERY THIN BAND OF
DEEP CONVECTION REMAINING BY THE 1300Z HOUR. THE INITIAL POSITION
IS PLACED WITH HIGH CONFIDENCE BASED ON THE 20-NM WIDE EYE FEATURE
IN THE EIR AND IS CURRENTLY QUASI-STATIONARY, HAVING MOVED ONLY
SLIGHTLY NORTHWARD OVER THE PAST SIX HOURS. A 250848Z SSMIS 89GHZ
MICROWAVE IMAGE SHOWED A DEVELOPING SECONDARY EYEWALL OUTSIDE THE
INNER EYEWALL, CONFIRMING AN ONGOING EYEWALL REPLACEMENT CYCLE. THE
INITIAL INTENSITY IS LOWERED TO A GENEROUS 130 KNOTS, BELOW THE
AGENCY CURRENT INTENSITY ESTIMATES OF T7.0 IN FAVOR OF THE ADT AND
SATCON ESTIMATES. ADDITIONALLY, A 250855Z SMAP FIX ESTIMATED
MAXIMUM WINDS OF 133 KNOTS. WHILE THE ENVIRONMENT REMAINS FAVORABLE
OVERALL, THE SYSTEM HAS BECOME QUASI-STATIONARY OVER A POOL OF
RELATIVELY LOW OHC VALUES AND IS EXPERIENCING THE EFFECTS OF
SIGNIFICANT UPWELLING. COUPLED MODELS INDICATE THE SSTS MAY BE AS
LOW AS 25-26C UNDER THE CORE. ADDITIONALLY, OUTFLOW WHILE ROBUST TO
THE NORTHEAST AND SOUTH, IS SOMEWHAT LIMITED TO THE NORTHWEST AS IT
BUTTS UP AGAINST SOME STRONG NORTHERLY FLOW NEAR THE 130E LINE. THE
COMBINED EFFECTS OF THE UPWELLING, THE ERC AND THE IMPINGEMENT OF
THE OUTFLOW TO THE NORTHWEST IS LEADING TO A PERIOD OF RAPID
WEAKENING, AS EVIDENCED BY THE DEGRADING STRUCTURE IN THE EIR.

INITIAL WIND RADII BASIS: PERSISTENCE. 

CURRENT STEERING MECHANISM: COMPETING STEERING ENVIRONMENT BETWEEN
A DEVELOPING SUBTROPICAL RIDGE (STR) CENTERED TO THE SOUTHEAST NEAR
GUAM, AND AN EXTENSION OF THE STR CENTERED WEST OF SHANGHAI,
EXTENDING EAST ALONG 30N TO ABOUT 140E. 

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T7.0 - 140 KTS 
   RJTD: T7.0 - 140 KTS 
   RCTP: T7.0 - 140 KTS 
   KNES: T7.0 - 140 KTS 
   CIMSS SATCON: 132 KTS AT 261011Z
   CIMSS ADT: 132 KTS AT 261130Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 5-10 KTS
   SST: 30-31 CELSIUS
   OUTFLOW: STRONG POLEWARD AND EQUATORWARD
   OTHER FACTORS: IMPINGEMENT OF OUTFLOW IN THE NORTHWEST SECTOR. 

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: SUPER TYPHOON 20W IS EXPECTED TO REMAIN NEARLY
QUASI-STATIONARY, DRIFTING GENERALLY NORTHWESTWARD AT LESS THAN 02
KNOTS FOR THE NEXT 12 TO 24 HOURS WHILE REMAINING TRAPPED IN THE
COMPETING STEERING ENVIRONMENT. BEGINNING AROUND TAU 36, THE STR TO
THE EAST IS FORECAST TO BUILD AND TRANSITION TO A HIGH-AMPLITUDE
ORIENTATION WHILE THE RIDGE TO THE NORTH IS FORECAST TO WEAKEN AND
ERODE FROM EAST TO WEST SIMULTANEOUSLY. THIS WILL ALLOW STY 20W TO
BREAK OUT OF THE WEAK STEERING PATTERN AND BEGIN TO SLOWLY
ACCELERATE TOWARDS THE NORTHWEST. THE SYSTEM IS EXPECTED TO
STEADILY INCREASE FORWARD SPEED AFTER TAU 48 WHILE TURNING NORTH
THEN NORTHEAST ALONG THE GRADIENT BETWEEN THE HIGH AMPLITUDE RIDGE
AND A STRONG MID-LATITUDE TROUGH MOVING EAST OVER JAPAN. IN THE
NEAR-TERM, DUE TO THE CONTINUED UPWELLING OF COOLER WATERS AND THE
ONGOING ERC, THE SYSTEM IS EXPECTED TO WEAKEN TO 110 KNOTS BY TAU
24. EVEN AFTER THE COMPLETION OF THE CURRENT ERC, THE SYSTEM IS NOT
EXPECTED TO INTENSIFY AS IT REMAINS OVER THE INDUCED COOL POOL.
ONCE THE SYSTEM STARTS MOVING OUT OF ITS CURRENT POSITION, OHC
BECOMES LESS OF A FACTOR, AND LOCALIZED SSTS WILL BE WARMER, WHICH
WILL ALLOW FOR A PERIOD OF INTENSIFICATION BETWEEN TAU 36 AND 48.
BY TAU 72, THE SYSTEM WILL START TO FEEL THE EFFECTS OF MODERATE
MID-LEVEL SHEAR AND DRY AIR, AND WILL START ON A GENERAL WEAKENING
TREND WHICH WILL CONTINUE THROUGH THE REMAINDER OF THE FORECAST.
THE SYSTEM IS EXPECTED TO BEGIN EXTRA-TROPICAL TRANSITION (ETT) AT
OR SLIGHTLY AFTER TAU 96 AS IT STARTS TO INTERACT WITH THE
UPPER-LEVEL WESTERLIES. BY TAU 120 THE ETT PROCESS WILL BE NEARLY
COMPLETE AS THE SYSTEM WILL BEGIN TO TAKE ON FRONTAL
CHARACTERISTICS AND WEAK THERMAL ADVECTION AS IT MOVES RAPIDLY
POLEWARD TO THE EAST OF HONSHU. AFTER TURNING NORTHEASTWARD, THE
WIND FIELD IS FORECAST TO EXPAND DRAMATICALLY AND WHILE THE TRACK
IS FORECAST TO REMAIN OFFSHORE, GALE TO STORM-FORCE WINDS CAN BE
EXPECTED ACROSS MUCH OF EASTERN HONSHU, INCLUDING THE TOKYO METRO
AREA. 

MODEL DISCUSSION: TRACK GUIDANCE REMAINS IN SURPRISINGLY GOOD
AGREEMENT THROUGH THE FORECAST PERIOD. CROSS-TRACK SPREAD IS 140 NM
AT TAU 72 AND INCREASE TO 190 NM BY TAU 120, WITH THE ENVELOPE
DEFINED BY NAVGEM TO THE WEST AND THE GFS ENSEMBLE MEAN ON THE
RIGHT. ALONG-TRACK SPREAD INCREASES AFTER TAU 96, UP TO 450 NM BY
TAU 120. THE JTWC FORECAST, WITH THE EXCEPTION OF SLOWER TRACK
SPEEDS THROUGH TAU 24, REMAINS CONSISTENT WITH THE PREVIOUS
FORECAST WITH HIGH CONFIDENCE THROUGH TAU 72 AND MEDIUM CONFIDENCE
THEREAFTER. INTENSITY GUIDANCE IS ALSO IN GOOD AGREEMENT, WITH ALL
MEMBERS INDICATING NEAR-TERM WEAKENING FOLLOWED BY A LEVELING OFF
AND THEN MORE SIGNIFICANT WEAKENING AFTER TAU 72. THE JTWC FORECAST
LIES NEAR THE CONSENSUS MEAN THROUGH TAU 24 THEN 5-10 KNOTS HIGHER
THAN THE MEAN THROUGH THE REMAINDER OF THE FORECAST. DUE TO THE
VERY RAPID WEAKENING OBSERVED IN METSAT AND THE POSSIBILITY THAT
THE BOTTOM COULD BE LOWER THAN PREDICTED, THERE IS LOW CONFIDENCE
IN THE JTWC INTENSITY FORECAST. 

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