WDPN31 PGTW 062100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 15W (FIFTEEN) 
WARNING NR 004//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 31.0N 156.8E
   INITIAL INTENSITY: 25 KTS
   GEOGRAPHIC REFERENCE: 434 NM NORTH-NORTHEAST OF MINAMI TORI
SHIMA
   MOVEMENT PAST 6 HOURS: NORTHWARD AT 13 KTS
   SIGNIFICANT WAVE HEIGHT: 12 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS TROPICAL
DEPRESSION (TD) 15W WITH A COMPLETELY EXPOSED LOW-LEVEL CIRCULATION
CENTER (LLCC) WITH SHALLOW CONVECTION DISPLACED FAR TO THE SOUTH.
THE WIND FIELD REMAINS ASYMMETRIC WITH THE WESTERN EXTENT OF THE
LLCC BECOMING VERY WEAK. ENVIRONMENTAL ANALYSIS INDICATES THAT 15W
IS IN AN UNFAVORABLE ENVIRONMENT CHARACTERIZED BY WEAK OUTFLOW
ALOFT, MODERATE TO HIGH (20-25 KTS) VERTICAL WIND SHEAR, DRY AIR
UPSTREAM OF THE SYSTEM, AND WARM (27-28 C) SEA SURFACE
TEMPERATURES. THE INITIAL POSITION IS PLACED WITH HIGH CONFIDENCE
BASED ON THE EXPOSED LLCC IN ANIMATED EIR IMAGERY. THE INITIAL
INTENSITY OF 25 KTS IS ASSESSED WITH HIGH CONFIDENCE BASED ON
PERSISTENCE FROM EARLIER SCATTEROMETER DATA AND OBJECTIVE INTENSITY
ESTIMATES ALL AROUND 25-30 KTS.

INITIAL WIND RADII BASIS: NOT APPLICABLE (THERE ARE NO INITIAL WIND
RADII).

CURRENT STEERING MECHANISM: WESTERN PERIPHERY OF A SUBTROPICAL
RIDGE POSITIONED TO THE EAST

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T1.5 - 25 KTS
   CIMSS SATCON: 32 KTS AT 061730Z
   CIMSS ADT: 26 KTS AT 061800Z
   CIMSS AIDT: 33 KTS AT 061800Z
   CIMSS D-MINT: 23 KTS AT 061509Z
   CIMSS D-PRINT: 26 KTS AT 061800Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: UNFAVORABLE
   VWS: 20-25 KTS
   SST: 27-28 CELSIUS
   OUTFLOW: WEAK EQUATORWARD
   OTHER FACTORS: DRY AIR TO THE NORTH

ANALYSIS CONFIDENCE:
   INITIAL POSITION: HIGH
   INITIAL INTENSITY: HIGH
   INITIAL WIND RADII: NOT APPLICABLE

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: TRUNCATED WARNING TO 24 HOURS

FORECAST DISCUSSION: TD 15W IS FORECAST TO CONTINUE TRACKING
NORTHWARD, ALONG THE WESTERN PERIPHERY OF THE SUBTROPICAL RIDGE TO
THE EAST, THROUGHOUT THE FORECAST PERIOD. THE SYSTEM IS EXPECTED TO
REMAIN IN AN UNFAVORABLE ENVIRONMENT AS IT TRACKS NORTHWARD,
PARTICULARLY WITH LARGE AMOUNTS OF DRY AIR. ADDITIONALLY, THE
ASYMMETRIC NATURE OF THE VORTEX IS EXPECTED TO HINDER ANY FURTHER
DEVELOPMENT, AND WILL AID IN UNRAVELING THE CIRCULATION. AS SUCH,
15W IS FORECAST TO WEAKEN AFTER TAU 12 AS THE SYSTEM BECOMES
ELONGATED AND THE WESTERN PORTION OF THE VORTEX OPENS UP.
DISSIPATION IS FORECAST TO OCCUR AROUND TAU 24.

MODEL DISCUSSION: NUMERICAL MODEL TRACK GUIDANCE IS IN GOOD
AGREEMENT OVER THE FIRST 12 HOURS. HOWEVER, THE MAJORITY OF VORTEX
TRACKERS LOSE THE CIRCULATION AFTERWARD, AS 15W WEAKENS. AS A
RESULT, THERE IS ONLY MEDIUM CONFIDENCE IN THE JTWC FORECAST TRACK.
INTENSITY GUIDANCE IS SPLIT, WITH THE STATISTICAL DYNAMICAL MODELS
KEEPING THE SYSTEM ABOVE TD STRENGTH MUCH LONGER THAN THE
REMAINDER OF GUIDANCE. THE JTWC INTENSITY FORECAST FOLLOWS CLOSELY
TO THE HAFS-A, WHICH DEPICTS A STEADY INTENSITY THROUGH TAU 12 AND
WEAKENING THEREAFTER.

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