WDPN31 PGTW 290900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 20W (MINDULLE) WARNING NR 028//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 24.2N 135.4E
   INITIAL INTENSITY: 115 KTS
   GEOGRAPHIC REFERENCE: 324 NM WEST OF IWO TO
   MOVEMENT PAST 6 HOURS: NORTHWARD AT 08 KTS
   SIGNIFICANT WAVE HEIGHT: 45 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS A SOLID BAND
OF DEEP CONVECTION WRAPPING AROUND THE PERIPHERY OF A WELL-DEFINED
30-NM WIDE EYE, WITH SOME POCKETS OF COLDER CLOUD TOPS FLARING
ALONG THE NORTHERN PERIPHERY. A 290130Z GMI 89GHZ MICROWAVE IMAGE
SHOWED THE SOLID BAND OF DEEP CONVECTION, IN THE EYEWALL, WITH SOME
BANDS OF WEAKER CONVECTION WRAPPING INTO THE CORE. THE INITIAL
POSITION IS ASSESSED WITH HIGH CONFIDENCE BASED ON THE 30-NM WIDE
EYE IN THE VISIBLE AND INFRARED IMAGERY. THE INITIAL INTENSITY
REMAINS STEADY, ASSESSED WITH HIGH CONFIDENCE AT 115 KNOTS BASED ON
A CONGRUENCE OF AGENCY FIXES AND OBJECTIVE ESTIMATES. THE
ENVIRONMENT REMAINS FAVORABLE, WITH LOW VWS, WARM SSTS AND GOOD
OUTFLOW ALOFT. OF NOTE, THE OUTFLOW PATTERN HAS SHIFTED, AND IS NO
LONGER RADIAL, EXCEPT FOR A SMALL REGION DIRECTLY OVER THE CENTER
EXTENDING ABOUT 100-NM OUT. BEYOND THAT, OUTFLOW TO THE WEST IS
BEING PINCHED BY STRONG SOUTHWESTERLIES AND SYNOPTIC SOUTHERLY FLOW
IS BEGINNING TO LIMIT THE OUTFLOW TO THE SOUTH. HOWEVER, POLEWARD
OUTFLOW REMAINS ROBUST, TURNING EQUATORWARD IN A BROAD, GRACEFUL
ARC TO THE EAST.

INITIAL WIND RADII BASIS: SCATTEROMETER DATA 

CURRENT STEERING MECHANISM: NORTHWEST PERIPHERY OF DEEP SUBTROPICAL
RIDGE (STR) CENTERED OVER THE MARIANAS. 

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T6.0 - 115 KTS
   RJTD: T6.0 - 115 KTS
   RCTP: T6.0 - 115 KTS
   KNES: T6.5 - 127 KTS
   CIMSS SATCON: 118 KTS AT 290431Z
   CIMSS ADT: 112 KTS AT 290540Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 0-5 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: STRONG POLEWARD
   OTHER FACTORS: MODERATE RADIAL OUTFLOW WITHIN 100-NM OF THE
CENTER. 

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. THE WARNING DURATION HAS
BEEN TRUNCATED TO 72 HOURS DUE TO EXTRA-TROPICAL TRANSITION. 

FORECAST DISCUSSION: AFTER A BRIEF SLOWDOWN, TY 20W IS NOW MOVING
STEADILY NORTHWARD ALONG THE WESTERN SIDE OF A NORTH TO SOUTH
ORIENTED STR SITTING OVER THE MARIANAS ISLAND CHAIN. THE RIDGE WILL
CONTINUE TO BUILD AND LAY BACK TO A MORE SOUTHWEST TO NORTHEAST
ORIENTATION OVER THE NEXT 12 TO 24 HOURS, AS A DEEP MID-LATITUDE
TROUGH CURRENTLY OVER EASTERN CHINA TRANSITS EAST. TY 20W WILL BE
CAUGHT IN THE STRENGTHENING GRADIENT BETWEEN THESE TWO SYSTEMS AND
ACCELERATE TO THE NORTHEAST AFTER TAU 12. NO SIGNIFICANT CHANGES
ARE EXPECTED IN THE ENVIRONMENT SURROUNDING TY 20W FOR THE NEXT 12
TO 18 HOURS, WHICH WILL ALLOW TO SYSTEM TO MAINTAIN 115 KNOT
INTENSITY THROUGH TAU 12. MID-LEVEL SHEAR AND DRY AIR BEGIN TO
EXERT AN IMPACT AS EARLY AS TAU 24, BUT BY TAU 36 WILL BEGIN TO
SIGNIFICANTLY DEGRADE THE SYSTEM, LEADING TO RAPID WEAKENING AFTER
TAU 36. AN EXTRA-TROPICAL LOW OVER THE KOREAN PENINSULA WILL
TRANSIT RAPIDLY NORTHEASTWARD OVER THE NEXT 36 HOURS, DRAGGING A
WEAK COLD FRONT ACROSS THE SEA OF JAPAN, WHERE IT WILL LIE IN WAIT
FOR TY 20W. AS EARLY AS TAU 36 TY 20W WILL BEGIN TO ENTRAIN SOME
COOL, DRY AIR FROM THE NORTHWEST AS IT BEGINS TO INTERACT WITH THE
BAROCLINIC ZONE. BY TAU 48 THE SYSTEM WILL BE IN THE FULL THROWS OF
EXTRA-TROPICAL TRANSITION (ETT) AS IT DRAGS IN STRONG NORTHWESTERLY
FLOW INTO THE CORE OF THE SYSTEM AND EMBEDS UNDER A 500 MB TROUGH.
ETT IS EXPECTED TO BE COMPLETED BY TAU 72 AS THE SYSTEM BECOMES
FRONTAL IN NATURE. 

MODEL DISCUSSION: TRACK GUIDANCE IS IN VERY GOOD AGREEMENT, BOTH IN
TERMS OF CROSS-AND ALONG-TRACK SPREAD. THE JTWC FORECAST REMAINS
CONSISTENT WITH THE PREVIOUS FORECAST, NEAR THE CONSENSUS MEAN,
WITH HIGH CONFIDENCE. INTENSITY GUIDANCE IS IN OVERALL GOOD
AGREEMENT, THOUGH THE DECAY-SHIPS GUIDANCE REMAINS AN OUTLIER ON
THE HIGH SIDE, INDICATING STEADY STATE THROUGH TAU 24, BEFORE
SHARPLY DROPPING TO ALIGN WITH THE REMAINDER OF THE GUIDANCE. THE
JTWC FORECAST CLOSELY FOLLOWS THE SHIPS GUIDANCE THROUGH TAU 24,
THEN SLIGHTLY ABOVE THE CONSENSUS MEAN THEREAFTER, WITH HIGH
CONFIDENCE. 

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