WDPN31 PGTW 091500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 21W (BARIJAT) 
WARNING NR 012//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 29.7N 149.0E
   INITIAL INTENSITY: 30 KTS
   GEOGRAPHIC REFERENCE: 578 NM EAST-SOUTHEAST OF YOKOSUKA, JAPAN
   MOVEMENT PAST 6 HOURS: NORTHWARD AT 20 KTS
   SIGNIFICANT WAVE HEIGHT: 15 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS TROPICAL
DEPRESSION 21W (BARIJAT) WITH A PARTIALLY EXPOSED LOW-LEVEL
CIRCULATION CENTER (LLCC) THAT HAS TRACKED QUICKLY NORTHWARD OVER
THE PAST 6 HOURS. NEAR 091200Z THE SYSTEM HAS STARTED TO FORM DEEP
CONVECTION OVER THE CENTER, SUGGESTING A MOISTENING OF THE CORE OF
THE VORTEX. ENVIRONMENTAL ANALYSIS INDICATES THAT 21W IS IN A
MARGINALLY FAVORABLE ENVIRONMENT FOR INTENSIFICATION CHARACTERIZED
BY MODERATE POLEWARD OUTFLOW ALOFT, LOW TO MODERATE (15-20 KTS)
VERTICAL WIND SHEAR, DRY AIR OVER THE WESTERN FLANK, AND WARM
(28-29 C) SEA SURFACE TEMPERATURES. THE INITIAL POSITION IS PLACED
WITH HIGH CONFIDENCE BASED ON THE PARTIALLY EXPOSED LLCC SEEN IN
THE ANIMATED EIR SATELLITE IMAGERY. THE INITIAL INTENSITY OF 30 KTS
IS ASSESSED WITH MEDIUM CONFIDENCE BASED ON THE AGENCY DVORAK AND
OBJECTIVE INTENSITY ESTIMATES LISTED BELOW.

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

CURRENT STEERING MECHANISM: WESTERN PERIPHERY OF A SUBTROPICAL
RIDGE (STR) POSITIONED TO THE EAST.

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T1.5 - 25 KTS
   RJTD: T2.0 - 30 KTS
   CIMSS ADT: 28 KTS AT 091200Z
   CIMSS AIDT: 34 KTS AT 091200Z
   CIMSS DPRINT: 31 KTS AT 091200Z
   CIMSS DMINT: 33 KTS AT 090813Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE
   VWS: 15-20 KTS
   SST: 28-29 CELSIUS
   OUTFLOW: MODERATE POLEWARD
   OTHER FACTORS: DRY AIR TO THE WEST.

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

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: RESTARTED WARNINGS FOR 21W DUE TO
IMPROVED STRUCTURE AND MODEL GUIDANCE SUGGESTING CONTINUED
DEVELOPMENT AS IT TRACKS POLEWARD. EXTRATROPICAL TRANSITION IS NOW 
FORECAST VICE DISSIPATION OVER WATER.

FORECAST DISCUSSION: 21W IS FORECAST TO BEGIN TRACKING GENERALLY
NORTHEASTWARD, ALONG THE WESTERN PERIPHERY OF A STR TO THE EAST
THROUGH TAU 48. THE ENVIRONMENT IS EXPECTED TO REMAIN SUBPAR
THROUGH TAU 24 WITH DRY AIR AND MODERATE SHEAR RESULTING IN NEARLY
STAGNANT INTENSITY THROUGH THAT TIME. AS THE SYSTEM NEARS THE JET,
POLEWARD OUTFLOW WILL VASTLY IMPROVE AND BAROCLINIC ENERGY WILL
ALLOW INTENSIFICATION TO AROUND 50 KTS AT TAU 48. EXTRATROPICAL
TRANSITION IS FORECAST TO BE COMPLETE NEAR TAU 48 AS 21W
TRANSITIONS INTO A COLD CORE SYSTEM WITH AN EXPANSIVE WIND FIELD 
SOUTH OF THE KAMCHATKA PENINSULA.

MODEL DISCUSSION: NUMERICAL MODEL GUIDANCE IS IN GOOD AGREEMENT
CONCERNING THE TRACK OF 21W WITH A 106 NM CROSS-TRACK SPREAD AT TAU
36. AT TAU 48, MODELS DIVERGE SLIGHTLY TO A 190 NM SPREAD DUE TO
DIFFERING INTERACTIONS WITH THE JET. NEVERTHELESS, THE JTWC TRACK
FORECAST IS PLACED CLOSE TO CONSENSUS WITH HIGH CONFIDENCE.
INTENSITY GUIDANCE IS IN MODERATE AGREEMENT SUGGESTING GRADUAL
INTENSIFICATION THROUGH TAU 36 WITH PEAK INTENSITIES OCCURRING AT
TAU 48 AS THE CYCLONE TRANSITIONS TO EXTRATROPICAL. THE JTWC
INTENSITY FORECAST IS PLACED WITH MEDIUM CONFIDENCE DUE TO POSSIBLE
VARIATIONS IN HOW THE VORTEX INTERACTS WITH THE BAROCLINIC ZONE.

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