WDPN32 PGTW 091500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 13W (PEILOU) WARNING NR
011//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 20.8N 144.0E
   INITIAL INTENSITY: 35 KTS
   GEOGRAPHIC REFERENCE: 429 NM NORTH OF ANDERSEN AFB
   MOVEMENT PAST 6 HOURS: EAST-SOUTHEASTWARD AT 13 KTS
   SIGNIFICANT WAVE HEIGHT: 14 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED PROXY VISIBLE (PROXYVIS) SATELLITE IMAGERY DEPICTS A
SMALL, PARTIALLY EXPOSED LOW-LEVEL CIRCULATION CENTER (LLCC) WITH
FLARING DEEP CONVECTION DEVELOPING IN THE NORTHEASTERN AND
SOUTHEASTERN QUADRANTS. A 091131Z ASCAT-B BULLSEYE PASS, REVEALED A
VERY COMPACT WIND FIELD ASSOCIATED WITH TS 13W WITH MAXIMUM WINDS
OF 35 KNOTS IN THE SOUTHEASTERN QUADRANT. ANIMATED WATER VAPOR
IMAGERY DEPICTS A DEEP UPPER-LEVEL TROUGH TO THE NORTHWEST, WHICH
IS INTRODUCING SOME DRY MID-LEVEL AIR ALONG THE FAR NORTHWESTERN
FLANK OF THE CIRCULATION BUT ALSO PROVIDING STRONG, DIVERGENT
POLEWARD OUTFLOW TO THE NORTHEAST, AHEAD OF THE TROUGH AXIS. THE
INITIAL POSITION IS ASSESSED WITH HIGH CONFIDENCE BASED ON THE
ASCAT PASS AND PROXYVIS IMAGERY. THE INITIAL INTENSITY IS ASSESSED
WITH HIGH CONFIDENCE BASED ON THE ALIGNMENT OF THE OBJECTIVE
INTENSITY ESTIMATES NOTED BELOW AND THE SCATTEROMETER DATA.
ENVIRONMENTAL CONDITIONS ARE MARGINALLY FAVORABLE, WITH STRONG
OUTFLOW ALOFT, LOW VWS, AND WARM SSTS OFFSET BY DRY AIR ENTRAINMENT
TO THE NORTHWEST AND THE EXTREMELY SMALL NATURE OF THE SYSTEM.

INITIAL WIND RADII BASIS: SCATTEROMETER DATA

CURRENT STEERING MECHANISM: NORTHERN FLANK OF AN ELONGATED NEAR
EQUATORIAL RIDGE (NER) AND ALONG A BELT OF LOW- TO MID-LEVEL
MONSOONAL SOUTHWESTERLIES

AGENCY DVORAK AND AUTOMATED FIXES:
   PGTW: T2.0 - 30 KTS
   RJTD: T1.5 - 25 KTS
   RCTP: T2.0 - 30 KTS
   KNES: T2.0 - 30 KTS
   CIMSS SATCON: 38 KTS AT 090910Z
   CIMSS ADT: 35 KTS AT 091200Z
   CIMSS AIDT: 34 KTS AT 091200Z
   CIMSS D-MINT: 35 KTS AT 090826Z
   CIMSS D-PRINT: 34 KTS AT 091240Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE
   VWS: 5-10 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: STRONG POLEWARD
   OTHER FACTORS: UPPER-LEVEL TROUGH IN CLOSE PROXIMITY TO THE
NORTHWEST.

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: TS 13W WILL CONTINUE TO TRACK SOUTHEASTWARD
FOR ANOTHER FEW, HOURS BEFORE GRADUALLY TURNING EASTWARD BY TAU 12.
THE SYSTEM THEN TURNS NORTHEASTWARD THROUGH THE REMAINDER OF THE
FORECAST PERIOD, TRAVELING ALONG THE NORTHERN PERIPHERY OF A LOW-
TO MID-LEVEL NER TO THE SOUTH. REGARDING INTENSITY, TS 13W WILL
STEADILY INTENSIFY OVER THE NEXT 24 HOURS AS IT MOVES EASTWARD
AHEAD OF THE UPPER-LEVEL TROUGH TO THE WEST AND REMAINS UNDER THE
DIVERGENT UPPER-LEVEL OUTFLOW REGION OF THE TROUGH, WHICH WILL
SUPPORT SUSTAINED CONVECTIVE DEVELOPMENT. AFTER TAU 24, SIGNIFICANT
DRY AIR IS FORECAST TO MOVE IN FROM THE WEST, ENGULF TS 13W, AND
MARK THE ONSET OF RAPID WEAKENING. INCREASED SHEAR AFTER TAU 48, AND
THE PASSAGE OF THE UPPER-LEVEL TROUGH TO THE EAST OF THE SYSTEM
WILL FINISH THE JOB STARTED BY THE DRY AIR ENTRAINMENT, AND TS 13W
WILL DISSIPATE AS A TROPICAL CYCLONE BY TAU 72.

MODEL DISCUSSION: TRACK GUIDANCE IS IN STRONG AGREEMENT THROUGH THE
FORECAST PERIOD, DISPLAYING MINIMAL CROSS- OR ALONG-TRACK SPREAD.
THE SOLE OUTLIER IS NAVGEM, WHICH BREAKS OFF FROM THE REMAINDER OF
THE PACK AFTER TAU 24 AND TURNS SHARPLY POLEWARD. THE JTWC FORECAST
TRACK IS PLACED NEAR THE AI CONSENSUS MEAN WITH HIGH CONFIDENCE.
INTENSITY GUIDANCE IS ALSO IN GOOD AGREEMENT WITH THE NOTABLE
EXCEPTION OF THE DECAY-SHIPS (GFS), WHICH DEPICTS UNREALISTIC RAPID
INTENSIFICATION AFTER TAU 36. THE BULK OF THE GUIDANCE MAINTAINS THE
SYSTEM AS A WEAK TROPICAL DEPRESSION OR MINIMAL TROPICAL STORM FROM
TAU 48 ONWARDS, THOUGH THE GFS AND HWRF BOTH SHOW THE SYSTEM
WEAKENING BELOW 25 KNOTS. THE JTWC FORECAST IS PLACED NEAR THE
HAFS-A AND HWRF THROUGH TAU 48, THEN DEVIATES BELOW THE GUIDANCE BY
TAU 72.

FORECAST CONFIDENCE:
   TRACK 00-72 HR: HIGH
   INTENSITY 00-72 HR: MEDIUM//
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