WDPN31 PGTW 271500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 20W (MINDULLE) WARNING NR 021//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 20.1N 136.4E
   INITIAL INTENSITY: 90 KTS
   GEOGRAPHIC REFERENCE: 392 NM SOUTHWEST OF IWO TO
   MOVEMENT PAST 6 HOURS: NORTHWESTWARD AT 03 KTS
   SIGNIFICANT WAVE HEIGHT: 42 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
TY 20W HAS COMPLETED OR NEARLY COMPLETED AN EYEWALL REPLACEMENT
CYCLE, WITH A 270700Z SSMIS 89GHZ MICROWAVE IMAGE CONFIRMING THE
DISSIPATION OF THE INNER EYEWALL AND THE DEVELOPMENT OF A MUCH
LARGER, BUT FRAGMENTED EYEWALL ABOUT 75 NM FROM THE CENTER.
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY AT THE 1200Z
DEPICTS DEEP CONVECTION DEVELOPING IN THE WESTERN PORTION OF THE
OUTER EYEWALL, AND THE EYEWALL DIAMETER BEGINNING TO CONSTRICT ONCE
MORE. THE PRESENCE OF DEEP CONVECTION IN THE EYEWALL FOR THE FIRST
TIME IN ABOUT 36 HOURS LIKELY MEANS THAT THE SYSTEM IS MOVING OUT
OF THE COLD POOL OF UPWELLED WATER AND INTO MORE FAVORABLE
OCEANOGRAPHIC CONDITIONS. NOW THAT THE ERC HAS EVIDENTLY FINISHED,
THE SYSTEM HAS LIKELY REACHED THE BOTTOM OF THE INTENSITY BARREL.
THE INITIAL POSITION IS PLACED WITH HIGH CONFIDENCE BASED ON THE
BROAD EYE FEATURE IN THE EIR AND AMONGST THE TIGHTLY CLUSTERED
AGENCY FIX POSITIONS. THE INITIAL INTENSITY IS ASSESSED AT 90 KNOTS
WITH HIGH CONFIDENCE BASED ON THE CONGRUENCE OF AGENCY CURRENT
INTENSITY ESTIMATES WHICH ALIGN NICELY WITH THE ADT AND SATCON
ESTIMATES. ENVIRONMENTAL CONDITIONS ARE IMPROVING NOW THAT THE
SYSTEM IS MOVING AWAY FROM THE COLD POOL. WHILE OHC VALUES ON THE
ROAD AHEAD ARE NOTHING TO WRITE HOME ABOUT, THEY ARE FAVORABLE,
ESPECIALLY FOR A SYSTEM THAT IS MOVING STEADILY DOWN TRACK.
OTHERWISE THE ENVIRONMENT REMAINS FAVORABLE FOR DEVELOPMENT.

INITIAL WIND RADII BASIS: SCATTEROMETER DATA 

CURRENT STEERING MECHANISM: THE STEERING ENVIRONMENT REMAINS WEAK,
WITH THE SYSTEM TRAPPED BETWEEN A DEVELOPING SUBTROPICAL RIDGE
(STR) CENTERED OVER THE CENTRAL MARIANAS AND AN EASTWARD EXTENSION
OF A STR LYING ALONG THE 30TH LATITUDE OUT TO ABOUT 140E. 

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T5.0 - 90 KTS
   RCTP: T5.0 - 90 KTS
   KNES: T5.0 - 90 KTS
   CIMSS SATCON: 85 KTS AT 270959Z
   CIMSS ADT: 87 KTS AT 271140Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 0-5 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: STRONG RADIAL

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

3. FORECAST REASONING.

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

FORECAST DISCUSSION: THE DEVELOPMENT OF A FAIRLY STRONG UPPER-LEVEL
CYCLONE EAST OF JAPAN AND THE PASSAGE OF THE ASSOCIATED UPPER-LEVEL
TROUGH CONTINUES TO ERODE THE EXTENSION OF THE STR LYING ALONG THE
30TH PARALLEL. NOW THAT THE RIDGE TO THE NORTH IS RETREATING, THE
BUILDING STR CENTERED NEAR GUAM IS QUICKLY ESTABLISHING DOMINANCE
OVER THE STEERING OF TY 20W. IN RESPONSE, TY 20W IS SLOWLY BUT
STEADILY STARTING TO TRACK TOWARDS THE NORTHWEST. OVER THE NEXT 48
HOURS THE TRACK WILL SLOWLY TURN TO THE NORTH AS THE RIDGE TAKES ON
A MORE NORTH-SOUTH AXIS AND MOVES NORTH ALONG WITH TY 20W. AFTER
TAU 48 TY 20W WILL ACCELERATE TO THE NORTHEAST AHEAD OF AN
APPROACHING MID-LATITUDE TROUGH MOVING IN FROM THE WEST. TY 20W HAS
BOTTOMED OUT FROM AN INTENSITY PERSPECTIVE AND NOW THAT ITS MOVING
AWAY FROM THE UPWELLING INDUCED COLD POOL, WILL HAVE ENOUGH OF AN
ENERGY SOURCE THAT, WHEN COMBINED WITH LOW SHEAR AND STRONG
OUTFLOW, WILL FUEL A PERIOD OF INTENSIFICATION THROUGH TAU 48.
THEREAFTER, SHEAR AND DRY AIR IN THE MID-LEVELS WILL LEAD TO SLOW
WEAKENING THROUGH TAU 72. SHEAR DRAMATICALLY INCREASES AFTER TAU
72, AND COMBINED WITH COOLER WATERS, WILL LEAD TO MORE RAPID
WEAKENING THROUGH THE REMAINDER OF THE FORECAST. THE SYSTEM IS
EXPECTED TO BEGIN EXTRATROPICAL TRANSITION (ETT) AROUND TAU 84 AND
SHOULD BE COMPLETE ETT AS A STORM FORCE LOW PRESSURE AREA NO LATER
THAN TAU 120, BUT LIKELY BY TAU 108 AS IT MOVES UNDER A 500 MB
SHORTWAVE, AND DEVELOPS THERMAL ADVECTION AND FRONTAL
CHARACTERISTICS. 

MODEL DISCUSSION: TRACK GUIDANCE IS IN REMARKABLY GOOD AGREEMENT
WITH A SPREAD OF ONLY 100 NM AT TAU 72, INCREASING TO A MODEST 200
NM AT TAU 120. ALONG-TRACK SPREAD DOES INCREASE A FAIR AMOUNT AFTER
TAU 96, REACHING 475 NM BY TAU 120. BUT THE MAJORITY OF THIS SPREAD
IS ACCOUNTED FOR BY THE UNREALISTICALLY PROGRESSION OF THE SYSTEM
AFTER TAU 72 AS DEPICTED BY THE NAVGEM. IF ONE DISCOUNTS NAVGEM,
THE ALONG TRACK SPREAD DECREASES TO ABOUT 330 NM. THE JTWC
FORECAST REMAINS CONSISTENT WITH THE PREVIOUS FORECAST, JUST INSIDE
AND SLIGHTLY SLOWER THAN THE CONSENSUS MEAN, WITH HIGH CONFIDENCE.
INTENSITY GUIDANCE IS ALSO IN GOOD AGREEMENT ON THE OVERALL
SCENARIO, WITH ALL MEMBERS EXCEPT COAMPS-TC TIGHTLY CLUSTERED IN A
15 KNOT ENVELOPE. THE JTWC FORECAST LIES ROUGHLY FIVE KNOTS ABOVE
THE MEAN THROUGHOUT THE FORECAST WITH MEDIUM CONFIDENCE. 

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