WDPN31 PGTW 092100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 21W (BARIJAT) 
WARNING NR 013//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 31.5N 149.2E
   INITIAL INTENSITY: 30 KTS
   GEOGRAPHIC REFERENCE: 527 NM EAST-SOUTHEAST OF YOKOSUKA, JAPAN
   MOVEMENT PAST 6 HOURS: NORTHWARD AT 16 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 CONTINUES TO TRACK NORTHWARD.
THROUGHOUT THE PREVIOUS SIX HOURS, CONTINUOUS FLARING CONVECTION
HAS PERSISTED ALONG THE NORTHERN PERIPHERY OF THE LLCC, WITH A
FRAGMENTED AND WEAK EQUATORWARD EXTENDING CHANNEL. ALONG THE
NORTHERN REACHES OF THE SYSTEMS RELATIVELY BROAD CIRCULATION, THE
MID-LATITUDE LONGWAVE PATTERN CONTINUES TO SUSTAIN THE SYSTEMS 30
KTS INTENSITY WITH A MODERATE UPPER-LEVEL OUTFLOW CHANNEL,
OBSERVABLE ON ANIMATED WATER VAPOR SATELLITE IMAGERY. ALTHOUGH THE
CURRENT ENVIRONMENT IS ASSESSED AS MARGINAL, THE CONVECTION
THROUGHOUT THE WESTERN SEMICIRCLE REMAINS EXTREMELY MINIMAL AS DRY
AIR WRAPS CYCLONICALLY INTO THE CORE AND THE SYSTEM MOVES NORTHWARD
INTO COOLER WATER, WHILE VERTICAL WIND SHEAR (VWS) REMAINS BETWEEN
25-30 KTS. THE INITIAL POSITION IS PLACED WITH MEDIUM CONFIDENCE
BASED ON THE PARTIALLY EXPOSED LLCC SEEN IN THE ANIMATED EIR
IMAGERY. THE INITIAL INTENSITY IS ASSESSED WITH MEDIUM CONFIDENCE
BASED ON THE AGENCY DVORAK AND OBJECTIVE INTENSITY ESTIMATES LISTED
BELOW. OF NOTE, AN EARLIER 091102Z ASCAT-C IMAGE HAS INDICATED
15-20 KTS INTENSITIES THROUGHOUT THE WESTERN PERIPHERY OF THE LLCC,
WHILE THE ELEVATED INTENSITIES OF 30 KTS ARE EXPECTED THROUGHOUT
THE EASTERN QUADRANT.

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: T2.0 - 30 KTS
   RJTD: T2.0 - 30 KTS
   CIMSS SATCON: 37 KTS AT 091800Z
   CIMSS ADT: 31 KTS AT 091830Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINAL
   VWS: 20-25 KTS
   SST: 26-27 CELSIUS
   OUTFLOW: MODERATE POLEWARD

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

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: FORECASTING THE BEGINNING OF
EXTRATROPICAL TRANSITION SOONER THAN EXPECTED.

FORECAST DISCUSSION: TD 21W IS FORECASTED TO BEGIN TRACKING
GENERALLY NORTH-NORTHEASTWARD ALONG THE WESTERN PERIPHERY OF THE
STR TO THE EAST THROUGHOUT THE REMAINDER OF THE FORECAST PERIOD.
THROUGH THE NORTH-NORTHEASTWARD TRACK INTO TAU 12, THE ENVIRONMENT
IS EXPECTED TO BECOME NON-CONDUCIVE FOR FURTHER TROPICAL
INTENSIFICATION, AS MID-LATITUDE INDUCED VERTICAL WIND SHEAR (VWS)
REMAINS ABOVE 25 KTS, SEA SURFACE TEMPERATURES (SST) DECREASE TO
BELOW 26 C BY TAU 24, AND DRY AIR CONTINUES TO ENTRAIN INTO THE
CENTRAL CORE. AS THE SYSTEM PROGRESSES FURTHER NORTHWARD, THE
DOWNSTREAM DIFFLUENT LENGTH OF A LONGWAVE TROUGH WILL QUICKEN THE
SYSTEMS EXTRATROPICAL TRANSITION INTO A COLD-CORE BAROCLINIC LOW BY
TAU 36. THROUGHOUT THE TD 21W EXTRATROPICAL TRANSITION, THE
BAROCLINIC ENVIRONMENT WILL EXPAND THE SURFACE WIND FIELD, WHILE
FURTHER DEEPENING WITH AID FROM THE MID-LATITUDE UPPER-LEVEL
OUTFLOW PATTERN WILL ALLOW FOR AN INCREASE IN SURFACE INTENSITIES
TO 40 KTS BY TAU 36.

MODEL DISCUSSION: NUMERICAL MODEL GUIDANCE IS IN GOOD AGREEMENT
THAT THE TRACK OF TD 21W WILL CONTINUE NORTH-NORTHEASTWARD OVER THE
NEXT 36 HOURS, WITH A CROSS-TRACK SPREAD OF 140 NM BY TAU 24. AFTER
TAU 24, MODELS BEGIN TO DIVERGE TO A CROSS-TRACK OF 204 NM BY TAU
36 AS THE INTERACTION WITH THE EASTWARD PROGRESSING LONGWAVE
TROUGH DIFFER SLIGHTLY BETWEEN DETERMINISTIC MODEL GUIDANCE. THE
JTWC TRACK FORECAST IS ALIGNED CLOSELY WITH THE NUMERICAL MODEL
CONSENSUS WITH MEDIUM CONFIDENCE. THE JTWC INTENSITY GUIDANCE IS IN
MODERATE AGREEMENT, ILLUSTRATING A SLOW AND GRADUAL INTENSIFICATION
THROUGHOUT THE REMAINDER OF THE FORECAST PERIOD AS TD 21W STARTS
ITS EXTRATROPICAL TRANSITION BY TAU 12. THE JTWC INTENSITY FORECAST
IS ASSESSED WITH MEDIUM CONFIDENCE BASED ON THE SYSTEMS INTERACTION
AS IT GAINS SUPPORT FROM THE MID-LATITUDE LONGWAVE PATTERN AND
BEGINS TO DEEPEN WITH INCREASED UPPER-LEVEL SUPPORT INTO A
BAROCLINIC COLD-CORE SYSTEM BY TAU 36.

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