WDPN32 PGTW 091500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 25W (MAN-YI) WARNING NR 
003//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 15.5N 157.8E
   INITIAL INTENSITY: 40 KTS
   GEOGRAPHIC REFERENCE: 757 NM EAST OF ANDERSEN AFB
   MOVEMENT PAST 6 HOURS: NORTHWESTWARD AT 15 KTS
   SIGNIFICANT WAVE HEIGHT: 14 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS A VERY
COMPACT TROPICAL STORM (TS), WITH A PARTIALLY EXPOSED LOW LEVEL
CIRCULATION CENTER (LLCC) ON THE NORTHWESTERN EDGE OF A SMALL
CENTRAL DENSE OVERCAST (CDO). A 091059Z ASCAT-B BULLSEYE PASS
REVEALED A HIGHLY ASYMMETRIC WIND FIELD, WITH THE LLCC PINCHED OFF
IN THE NORTHEASTERN CUSP OF A WAVE FEATURE. WINDS ALONG THE
SOUTHWESTERN SIDE OF THE CIRCULATION ARE QUITE WEAK, AND THE
ENTIRETY OF GALE-FORCE WINDS CONFINED TO THE EASTERN HEMISPHERE.
THE STRONGEST WINDS, UP TO 50 KNOTS IN THE ULTRA-HIGH RESOLUTION
(UHR) ASCAT DATA, ARE RAIN FLAGGED AND UNDER THE DEEPEST CONVECTION
IN THE NORTHEAST SECTOR OF THE CIRCULATION. THE INITIAL POSITION IS
ASSESSED WITH HIGH CONFIDENCE BASED ON THE PARTIALLY EXPOSED LLCC
IN THE ANIMATED EIR, AND AN EXTRAPOLATION OF THE CENTER EVIDENT IN
THE ASCAT DATA. THE INITIAL INTENSITY IS SET AT 40 KNOTS, WITH
MEDIUM CONFIDENCE BASED ON THE GENERAL CONGRUENCE OF THE AVAILABLE
SUBJECTIVE AND OBJECTIVE INTENSITY ESTIMATES OUTLINED ABOVE, AND
ANALYSIS OF THE NON-FLAGGED ASCAT WINDS. THE ENVIRONMENT IS
MARGINALLY FAVORABLE, WITH WARM SSTS AND GOOD POLEWARD OUTFLOW
OFFSET BY THE SMALL SIZE OF THE SYSTEM AND THE MODERATE WESTERLY
SHEAR.

INITIAL WIND RADII BASIS: SCATTEROMETER DATA 

CURRENT STEERING MECHANISM: SOUTHWESTERN PERIPHERY OF A DEEP-LAYER
SUBTROPICAL RIDGE (STR) CENTERED NEAR THE DATELINE.

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T1.5 - 25 KTS
   RJTD: T2.0 - 30 KTS
   RCTP: T2.0 - 30 KTS
   KNES: T2.0 - 30 KTS
   CIMSS SATCON: 39 KTS AT 091200Z
   CIMSS ADT: 37 KTS AT 091230Z
   CIMSS AIDT: 36 KTS AT 091230Z
   CIMSS D-MINT: 33 KTS AT 090754Z
   CIMSS D-PRINT: 41 KTS AT 091200Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE
   VWS: 15-20 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: MODERATE POLEWARD

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

3. FORECAST REASONING.

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

FORECAST DISCUSSION: TROPICAL STORM 25W WILL CONTINUE TO TRACK
NORTHWESTWARD ALONG THE SOUTHWEST SIDE OF A DEEP STR FOR THE NEXT
24 HOURS. BY TAU 24 TRACK SPEEDS WILL SLOW DOWN A BIT, AS THE
STEERING PATTERN WEAKENS AND THE PRIMARY STEERING INFLUENCE SHIFTS
FROM THE STR TO THE NORTHEAST TO A STR TO THE NORTHWEST. AFTER TAU
24, THE TRACK WILL FLATTEN OUT TO A MORE WESTWARD DIRECTION AS THE
STEERING RIDGE SLIDES BY TO A POSITION DUE NORTH OF TS 25W. AFTER
TAU 48, THE SYSTEM BEGINS TO TAKE ON A MORE SOUTHWESTWARD TRACK AS
IT COMES UNDER THE STEERING INFLUENCE OF A THIRD AREA OF RIDGING
THAT DEVELOPS EAST OF OKINAWA. IN TERMS OF INTENSITY, MOST GLOBAL
AND MESOSCALE MODELS AGREE THAT A POINT SOURCE IS EXPECTED TO
DEVELOP ALOFT OVER THE SYSTEM IN THE NEXT 12 HOURS, REDUCING
DEEP-LAYER SHEAR OVER THE SYSTEM AND ALLOWING IT TO INTENSIFY.
THESE FAVORABLE CONDITIONS ARE EXPECTED TO CONTINUE THROUGH TAU 24,
AND THE SYSTEM IS FORECAST TO REACH PEAK INTENSITY OF 55 KNOTS
WITHIN THE NEXT 24 HOURS. AROUND TAU 36, AN INCREASE IN WESTERLY
MID-LEVEL SHEAR WILL BEGIN TO IMPINGE UPON THE ALREADY
RELATIVELY WEAK VORTEX, AND TS 25W WILL START TO WEAKEN. BY TAU 48,
DEEP-LAYER SHEAR INCREASES SHARPLY, USHERING IN AN EXTENSIVE LAYER
OF DRY AIR OVER TOP OF THE SYSTEM. THE COMBINED EFFECTS OF THE HIGH
SHEAR AND DRY AIR WILL USHER IN THE DEMISE OF TS 25W, WHICH WILL
STEADILY WEAKEN THROUGH THE REMAINDER OF THE FORECAST PERIOD AS THE
REMNANT VORTEX SLOWLY SPINS DOWN. 

MODEL DISCUSSION: DETERMINISTIC TRACK GUIDANCE IS IN GOOD AGREEMENT,
WITH THE EXCEPTION OF THE NAVGEM, WHICH TAKES THE SYSTEM POLEWARD
AND LOOPS BACK TO THE EAST ON AN UNREALISTIC TRACK. THE REMAINDER
OF THE GUIDANCE IS TIGHTLY PACKED AROUND THE JTWC FORECAST TRACK,
WITH A CROSS-TRACK UNCERTAINTY OF 125NM AT TAU 72 BETWEEN THE GFS
TO THE SOUTH AND THE JGSM ON THE NORTH. CROSS-TRACK SPREAD VARIES
LITTLE THROUGH THE END OF THE FORECAST PERIOD. THE JTWC FORECAST
LIES ON THE NORTHERN SIDE OF THE GUIDANCE ENVELOPE THROUGH TAU 72,
THEN CLOSE TO THE CONSENSUS MEAN, ROUGHLY IN THE MIDDLE OF THE
GUIDANCE ENVELOPE, THROUGH TAU 120. INTENSITY GUIDANCE IS IN GOOD
AGREEMENT THAT THE SYSTEM WILL INTENSIFY THROUGH TAU 24, FOLLOWED
BY A STEADY WEAKENING TREND THROUGH THE REMAINDER OF THE FORECAST.
THE HWRF AND HAFS-A INDICATE A PEAK BETWEEN 60-70 KNOTS, WHILE THE
CTCX SHOWS A PEAK OF JUST 50 KNOTS. THE JTWC FORECAST FOLLOWS THE
CONSENSUS MEAN THROUGH THE ENTIRE FORECAST PERIOD. 

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