WDPN32 PGTW 022100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 13W (THIRTEEN) WARNING 
NR 004//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 31.0N 140.5E
   INITIAL INTENSITY: 35 KTS
   GEOGRAPHIC REFERENCE: 261 NM SOUTH OF YOKOSUKA, JAPAN
   MOVEMENT PAST 6 HOURS: NORTH-NORTHEASTWARD AT 16 KTS
   SIGNIFICANT WAVE HEIGHT: 18 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) REVEALS A SLOWLY
ORGANIZING LOW-LEVEL CIRCULATION CENTER (LLCC) ASSOCIATED WITH
TROPICAL STORM (TS) 13W. THE SYSTEM REMAINS HIGHLY ASYMMETRIC,
HOWEVER MULTIPLE VORTICES PREVIOUSLY OBSERVED APPEAR TO BE
CONSOLIDATING WITH CONVECTIVE FLARE-UPS BUILDING ALONG THE
PERIPHERY. TS 13W IS CURRENTLY EMBEDDED WITHIN A MARGINALLY
FAVORABLE ENVIRONMENT, CHARACTERIZED BY ELEVATED MOISTURE CONTENT
THROUGHOUT THE ATMOSPHERIC COLUMN, WARM SEA SURFACE TEMPERATURES
(SST) RANGING BETWEEN 27 AND 28 C, LOW VERTICAL WIND SHEAR (VWS) OF
5-10 KTS, AND MODERATE POLEWARD OUTFLOW. THE PRIMARY LIMITING
FACTORS TO DEVELOPMENT ARE RESIDUAL VORTEX ASYMMETRY, AS WELL AS
VAST EXTENSION OF DRY, DEEP-LAYER AIR TO THE WEST AND NORTHWEST.
THE INITIAL POSITION IS DETERMINED WITH MEDIUM CONFIDENCE BASED ON
THE ANIMATED SHORTWAVE INFRARED AND VISIBLE SATELLITE IMAGERY LOOPS, 
SUPPORTED BY THE EXTRAPOLATION FROM A 021715Z ATMS MICROWAVE PASS. 
THE INITIAL INTENSITY OF 35 KTS IS ALSO ESTIMATED WITH MEDIUM 
CONFIDENCE, BASED ON A 021420 OCEANSAT-3 OSCAT PASS, IMPROVED 
CONVECTIVE ACTIVITY,
AND DVORAK FIXES AND AUTOMATED INTENSITY AIDS PROVIDED BELOW.

INITIAL WIND RADII BASIS: A 021420 OCEANSAT-3 OSCAT PASS

CURRENT STEERING MECHANISM: DEEP-LAYER SUBTROPICAL RIDGE (STR) TO
THE EAST

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.0 - 30 KTS
   KNES: T1.5 - 25 KTS
   CIMSS SATCON: 44 KTS AT 021625Z
   CIMSS ADT: 31 KTS AT 021730Z
   CIMSS AIDT: 39 KTS AT 021730Z
   CIMSS D-MINT: 25 KTS AT 021625Z
   CIMSS D-PRINT: 26 KTS AT 021830Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE
   VWS: 5-10 KTS
   SST: 27-28 CELSIUS
   OUTFLOW: MODERATE POLEWARD
   OTHER FACTORS: DRY AIR TO THE WEST

ANALYSIS CONFIDENCE:
   INITIAL POSITION: MEDIUM
   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: TS 13W IS EXPECTED TO PROPAGATE ALONG THE
NORTHWESTERN PERIPHERY OF A STEERING RIDGE CENTERED TO THE EAST
DURING THE FIRST 48 HOURS. OVER THIS PERIOD, ENVIRONMENTAL
CONDITIONS WILL REMAIN MARGINALLY FAVORABLE, WITH THE SYSTEM
FORECAST TO REACH A MODERATE INTENSITY OF 40 KTS, AS IT STRUGGLES TO 
CONSOLIDATE AND ALIGN VERTICALLY. BETWEEN TAUS 36 AND 48, TS 13W IS 
EXPECTED TO SLOW DOWN, AS THE STEERING PATTERN WEAKENS. AFTER TAU 48, 
THE SYSTEM WILL BEGIN A SLIGHTLY POLEWARD TURN AS IT ENCOUNTERS A 
SECONDARY, EXPANDING STR TO THE SOUTHEAST. COOLER SST AND INCREASING 
DRY AIR ENTRAINMENT WILL TRIGGER A WEAKENING TREND, COINCIDING WITH 
THE BEGINNING OF EXTRATROPICAL TRANSITION (ETT). TS 13W IS EXPECTED 
TO COMPLETE THE ETT BY TAU 96.

MODEL DISCUSSION: NUMERICAL TRACK MODEL GUIDANCE REMAINS IN FAIR
AGREEMENT THROUGHOUT THE FORECAST PERIOD, WITH ALL MODELS CONCURRING 
ON THE GENERAL STEERING PATTERN. CROSS-TRACK SPREAD AT TAU 24 IS 
CALCULATED AT 45 NM. TRACK GUIDANCE UNCERTAINTY INCREASES 
SIGNIFICANTLY AFTER TAU 72, DUE TO BRIEFLY WEAKENING STEERING
MECHANISM, RESULTING IN THE CROSS-TRACK SPREAD EXPANDING TO 170 NM.
JTWC INTENSITY FORECAST IS ASSESSED WITH MEDIUM CONFIDENCE OVERALL
DUE TO MIXED GUIDANCE AMONG THE AVAILABLE CONSENSUS MEMBERS.
STATISTICAL-DYNAMICAL MODELS PREDICT INTENSIFICATION TO A PEAK OF
50-55 KTS, WHILE DETERMINISTIC GFS MAINTAINS INTENSITY AROUND 35
KTS. ON THE OTHER END OF THE SPECTRUM LIES NAVGEM-DRIVEN COAMPS-TC
PREDICTING IMMEDIATE WEAKENING. OFFICIAL JTWC INTENSITY FORECAST IS
LAID CLOSE TO THE CONSENSUS MEAN, BEING SLIGHTLY ABOVE MAJORITY OF
THE DETERMINISTIC GUIDANCE.

FORECAST CONFIDENCE:
   TRACK 00-72 HR: HIGH
   TRACK 72-120 HR: MEDIUM
   INTENSITY 00-72 HR: MEDIUM
   INTENSITY 72-120 HR: MEDIUM//
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