WDPN32 PGTW 032100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 13W (BAILU) WARNING NR 
008//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 36.7N 147.2E
   INITIAL INTENSITY: 35 KTS
   GEOGRAPHIC REFERENCE: 335 NM EAST-NORTHEAST OF NARITA AIRPORT
   MOVEMENT PAST 6 HOURS: EAST-NORTHEASTWARD AT 17 KTS
   SIGNIFICANT WAVE HEIGHT: 17 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS A
GRADUALLY CONSOLIDATING LOW-LEVEL CIRCULATION CENTER (LLCC)
ASSOCIATED WITH TROPICAL STORM (TS) 13W (BAILU). THE SYSTEM STILL
EXHIBITS PRONOUNCED STRUCTURAL ASYMMETRY, INCLUDING HIGHLY
ASYMMETRIC WIND FIELD. HOWEVER, MULTIPLE MESOVORTICES PREVIOUSLY
EMBEDDED WITHIN THE BROADER CIRCULATION APPEAR TO HAVE MERGED INTO
A SINGLE VORTEX. CENTRAL CONVECTION IS WEAK, BUT RELATIVELY
PERSISTENT. THE INITIAL POSITION IS ASSESSED WITH HIGH CONFIDENCE
BASED ON A NEARLY FULLY EXPOSED LLCC PRESENT IN THE SHORTWAVE
INFRARED SATELLITE ANIMATION. INITIAL INTENSITY IS SET AT 35 KTS
WITH MEDIUM CONFIDENCE, BASED ON AGENCY DVORAK ESTIMATES AND
AUTOMATED AIDS LISTED BELOW. TS 13W IS CURRENTLY SITUATED IN A
MARGINALLY CONDUCIVE SYNOPTIC ENVIRONMENT, CHARACTERIZED BY LOW TO
MODERATE (15-20 KTS) VERTICAL WIND SHEAR (VWS) AND STRONG POLEWARD
OUTFLOW ALOFT, OFFSET BY BORDERLINE (25-26 C) SEA SURFACE
TEMPERATURES (SST) AND SIGNIFICANT ENTRAINMENT OF DRY AIR FROM THE
WEST.

INITIAL WIND RADII BASIS: OBJECTIVE BEST TRACK 

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

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.5 - 35 KTS
   RJTD: T2.0 - 30 KTS
   KNES: T2.0 - 30 KTS
   CIMSS SATCON: 44 KTS AT 031605Z
   CIMSS ADT: 33 KTS AT 031730Z
   CIMSS AIDT: 41 KTS AT 031730Z
   CIMSS D-MINT: 28 KTS AT 031827Z
   CIMSS D-PRINT: 28 KTS AT 031910Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINAL
   VWS: 15-20 KTS
   SST: 25-26 CELSIUS
   OUTFLOW: STRONG POLEWARD
   OTHER FACTORS: DRY AIR ENTRAINING FROM THE WEST

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

3. FORECAST REASONING.

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

FORECAST DISCUSSION: TS 13W IS FORECAST TO CONTINUE TRACKING
EAST-NORTHEASTWARD ALONG THE PERIPHERY OF A SUBTROPICAL RIDGE (STR)
POSITIONED TO THE SOUTHEAST DURING THE NEXT 24 HOURS. DURING THIS
INTERVAL, THE ENVIRONMENT WILL REMAIN MARGINALLY SUPPORTIVE FOR
FURTHER DEVELOPMENT, ALLOWING THE SYSTEM TO MAINTAIN ITS CURRENT
INTENSITY, OR PERHAPS INTENSIFY SLIGHTLY, IF IT MANAGES TO ACHIEVE
FULL VERTICAL COHERENCE. AROUND TAU 36, FORWARD MOTION IS EXPECTED
TO SLOW AS THE SYNOPTIC STEERING GRADUALLY WEAKENS. BEYOND TAU 48,
TS 13W IS ANTICIPATED TO BEGIN A GRADUAL RECURVATURE TO THE
NORTH-NORTHEAST, IN RESPONSE TO A BUILDING SECONDARY STR TO THE
SOUTHEAST. DECREASING OCEAN HEAT CONTENT, COMBINED WITH INCREASING
DRY AIR ENTRAINMENT AND REDUCED CONVECTIVE ORGANIZATION, WILL
INITIATE A WEAKENING TREND. SIMULTANEOUSLY, EXTRATROPICAL
TRANSITION (ETT) IS EXPECTED TO COMMENCE SHORTLY THEREAFTER, WITH
FULL TRANSITION PROJECTED TO COMPLETE SHORTLY AFTER TAU 72, AND NO
LATER THAN TAU 96.

MODEL DISCUSSION: NUMERICAL TRACK MODEL GUIDANCE IS IN RELATIVELY
GOOD AGREEMENT THROUGHOUT THE FORECAST PERIOD, WITH CONSISTENT
DEPICTION OF THE SYNOPTIC-SCALE STEERING REGIME. CROSS-TRACK SPREAD
AT TAU 24 IS APPROXIMATELY 40 NM. AFTER TAU 72, MODEL DIVERGENCE
INCREASES TO APPROXIMATELY 70 NM, REFLECTING UNCERTAINTY IN THE
EVOLVING STEERING FLOW. THE JTWC INTENSITY FORECAST IS ISSUED WITH
MEDIUM CONFIDENCE, DUE TO DISPARITY BETWEEN GUIDANCE MEMBERS.
COAMPS-TC AND STATISTICAL-DYNAMICAL AIDS SUGGEST SLIGHT
INTENSIFICATION TO 40 KTS, WHILE HAFS AND THE GFS DETERMINISTIC RUN
MAINTAIN A NEARLY FLAT INTENSITY FOR THE INITIAL 36 HOURS. THE
OFFICIAL JTWC INTENSITY FORECAST IS POSITIONED NEAR THE MULTI-MODEL
CONSENSUS MEAN, SLIGHTLY ABOVE MOST DETERMINISTIC SOLUTIONS.

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