WDPN31 PGTW 080300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 21W (TWENTYONE) 
WARNING NR 008//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 24.0N 147.0E
   INITIAL INTENSITY: 30 KTS
   GEOGRAPHIC REFERENCE: 315 NM EAST OF IWO TO
   MOVEMENT PAST 6 HOURS: NORTHWESTWARD AT 03 KTS
   SIGNIFICANT WAVE HEIGHT: 19 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS A FULLY
EXPOSED LOW-LEVEL CIRCULATION CENTER (LLCC) TO THE WEST OF THE
CONVECTION, INDICATING A STILL EXISTING, STRONG VERTICAL WIND SHEAR
(VWS) INHIBITING THE CONTINUOUS DEVELOPMENT OF TROPICAL DEPRESSION
21W. THE INITIAL POSITION IS PLACED WITH HIGH CONFIDENCE BASED ON
THE ANIMATED IMAGERY LOOP, AS WELL AS A 072311Z METOPB ASCAT PASS.
THE INITIAL INTENSITY OF 30 KTS IS ASSESSED WITH HIGH CONFIDENCE
BASED ON THE AFOREMENTIONED ASCAT PASS, AS WELL AS THE AGENCY AND
AUTOMATED ESTIMATES LISTED BELOW.

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

CURRENT STEERING MECHANISM: A SUBTROPICAL RIDGE (STR) TO THE EAST

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.5 - 35 KTS
   RJTD: T1.5 - 25 KTS
   KNES: T2.0 - 30 KTS
   CIMSS SATCON: 38 KTS AT 080000Z
   CIMSS ADT: 33 KTS AT 080000Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE
   VWS: 25-30 KTS
   SST: 28-29 CELSIUS
   OUTFLOW: MODERATE EASTWARD

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

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: NONE.

FORECAST DISCUSSION: AFTER TD 21W MADE A WEST-NORTHWESTWARD TURN SINCE 
THE LAST WARNING, THE ASSOCIATED CONVECTION HAS BEEN COMPLETELY BLOWN 
AWAY BY THE STRONG VWS FROM THE SOUTHWEST. AS THE SYSTEM TRANSITS 
THROUGH THE HIGH VWS REGION AND ROUNDS THE AXIS OF THE STR TO THE 
EAST, IT IS FORECAST TO START TURNING NORTH-NORTHEASTWARD. WITH 
DECREASING VWS AND HIGH SEA SURFACE TEMPERATURES, TD 21W IS FORECAST 
TO STEADILY INTENSIFY REACHING 60 KTS BY TAU 72. AT THAT TIME IT WILL 
BEGIN THE EXTRATROPICAL TRANSITION, AS IT INTERACTS WITH THE 
BAROCLINIC ZONE AND THE JET STREAM. 21W IS FORECAST TO COMPLETE THE 
TRANSITION BY THE END OF THE FORECAST PERIOD - WITHIN 96 HOURS.

MODEL DISCUSSION: DETERMINISTIC MODEL GUIDANCE IS IN FAIR AGREEMENT
WITH ALL TRACKERS ESTIMATING A NORTHWESTWARD DIRECTION, WITH A
SLIGHTLY DECREASED CONFIDENCE SINCE LAST WARNING. THE CURRENT
CROSS-TRACK SPREAD IS 70-80 NM. INTENSITY GUIDANCE IS IN GOOD
AGREEMENT, WITH ALL ESTIMATES PROJECTING STEADY INTENSIFICATION OUT
TO TAU 72. UPON ENTERING THE BAROCLINIC ZONE THE SYSTEM WILL
RAPIDLY WEAKEN AND BECOME PART OF THE DOMINANT WIND FLOW.

FORECAST CONFIDENCE:
   TRACK 0 - 72 HR: MEDIUM
   TRACK 72-120 HR: HIGH
   INTENSITY 0 - 72 HR: MEDIUM
   INTENSITY 72-120 HR: MEDIUM//
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