WDPN31 PGTW 110300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 06W (SIX) WARNING 
NR 001//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 25.0N 140.4E
   INITIAL INTENSITY: 30 KTS
   GEOGRAPHIC REFERENCE: 50 NM WEST-NORTHWEST OF IWO TO
   MOVEMENT PAST 6 HOURS: NORTHWESTWARD AT 09 KTS
   SIGNIFICANT WAVE HEIGHT: 12 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS TROPICAL
DEPRESSION (TD) 06W WITH A WELL-DEFINED, EXPOSED LOW-LEVEL
CIRCULATION CENTER (LLCC) AND FLARING CONVECTION DISPLACED TO THE
SOUTH. DEEP CONVECTION WAS PREVIOUSLY (AT AROUND 2200Z) BUILDING
OVER THE CENTER OF THE SYSTEM, BUT HAS SINCE BEEN SHEARED OFF TO
THE SOUTHEAST. A 102118Z WSFM 89 GHZ MICROWAVE IMAGE SHOWS THE
TIGHTLY WRAPPING LOW-LEVEL CLOUD LINES WITH ISOLATED POCKETS OF DEEP
CONVECTION WITHIN THE SOUTHERN PERIPHERY. ENVIRONMENTAL ANALYSIS
INDICATES THAT 06W IS IN A MARGINALLY FAVORABLE ENVIRONMENT
CHARACTERIZED BY MODERATE EASTWARD OUTFLOW ALOFT, MODERATE (15-20
KTS) NORTHWESTERLY VERTICAL WIND SHEAR, AND WARM (28-29 C) SEA
SURFACE TEMPERATURES. AN UPPER-LEVEL TROUGH IS CURRENTLY EXTENDING
OVER THE SYSTEM, PREVENTING CONVECTION FROM BUILDING OVER THE
CENTER AND CAUSING THE ELEVATED SHEAR. THE INITIAL POSITION IS
PLACED WITH HIGH CONFIDENCE BASED ON THE EXPOSED LLCC IN ANIMATED
MSI. THE INITIAL INTENSITY OF 30 KTS IS ALSO ASSESSED WITH HIGH
CONFIDENCE BASED ON SURFACE OBSERVATIONS FROM IWO TO REPORTING 28
KTS AT 2100Z AS THE CIRCULATION PASSED ABOUT 20 NM TO THE WEST OF
THE ISLAND.

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

CURRENT STEERING MECHANISM: WEAK RIDGING EXTENDING FROM AN
ELONGATED SUBTROPICAL RIDGE POSITIONED FAR OFF TO THE NORTHEAST.

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T1.5 - 25 KTS
   KNES: T1.5 - 25 KTS

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE
   VWS: 15-20 KTS
   SST: 28-29 CELSIUS
   OUTFLOW: MODERATE EASTWARD
   OTHER FACTORS: INTERACTION WITH AN UPPER-LEVEL TROUGH EXTENDING
OVER THE TOP OF THE SYSTEM.

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

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: THIS INITIAL PROGNOSTIC REASONING
MESSAGE ESTABLISHES THE FORECAST PHILOSOPHY.

FORECAST DISCUSSION: 06W IS FORECAST TO BEGIN TRACKING SLOWLY
NORTHWARD AND THEN NORTHEASTWARD AS RIDGING BUILDS IN TO THE EAST
OF THE SYSTEM OVER THE NEXT 36 HOURS. DEEP-LAYER CYCLONIC TURNING
TO THE NORTH OF THE SYSTEM WILL PREVENT A STRAIGHT NORTHWARD TRACK
AND WILL GUIDE THE VORTEX NORTHEASTWARD THROUGH TAU 48. STARTING AT
TAU 48, TRACK SPEEDS ARE EXPECTED TO INCREASE AS THE STEERING
PATTERN BECOMES MUCH MORE DEFINED DUE TO THE WESTWARD PROPAGATION
OF THE SUBTROPICAL RIDGE. THIS WILL CAUSE 06W TO TRACK NORTHWARD
THROUGH TAU 72. NEAR TAU 84, AN INCOMING LONGWAVE TROUGH WILL
ABSORB THE VORTEX AND PULL IT QUICKLY OFF TO THE NORTHEAST.
EXTRATROPICAL TRANSITION IS FORECAST TO COMPLETE NEAR TAU 96 AS THE
SYSTEM BECOMES EXTREMELY ELONGATED AND EMBEDDED WITHIN THE
UPPER-LEVEL JET MAX. REGARDING INTENSITY, 06W IS FORECAST TO
GRADUALLY INTENSIFY OVER THE NEXT 48 HOURS. SHEAR IS EXPECTED TO
REMAIN RELATIVELY HIGH THROUGHOUT THE FORECAST PERIOD (15-20
KTS) AS A SERIES OF UPPER-LEVEL CYCLONES INTERACT WITH THE SYSTEM.
HOWEVER, OUTFLOW WILL BE ENHANCED IN THE EASTWARD AND POLEWARD
DIRECTIONS, ALLOWING FOR THE INTENSIFICATION. GALE-FORCE WINDS ARE
EXPECTED TO BE PRIMARILY CONFINED TO THE EASTERN SEMICIRCLE OF THE
SYSTEM. AFTER TAU 48, DRY AIR WILL START TO BE ENTRAINED INTO THE
CORE OF THE VORTEX, HALTING FURTHER INTENSIFICATION. AN INTENSITY
NEAR 45 KTS IS THEN FORECAST TO PERSIST THROUGH THE REMAINDER OF
THE FORECAST PERIOD AS 06W TRANSITIONS INTO AN EXTRATROPICAL
CYCLONE.

MODEL DISCUSSION: NUMERICAL MODEL GUIDANCE IS IN MODERATE AGREEMENT
WITH THE EXCEPTION OF GALWEM, WHICH TRACKS THE VORTEX OFF TO THE
NORTHWEST RATHER THAN NORTHEAST AFTER TAU 48. DISCOUNTING GALWEM,
DETERMINISTIC AND ENSEMBLE MODELS AGREE ON THE TRAJECTORY OF 06W.
AFTER TAU 72, MODELS GREATLY DIVERGE DUE TO DIFFERENCES IN
INTERACTION WITH THE UPPER-LEVEL TROUGH. AS A RESULT, THE JTWC
TRACK FORECAST IS PLACED WITH MEDIUM CONFIDENCE THROUGH TAU 72 AND
LOW CONFIDENCE THEREAFTER. INTENSITY GUIDANCE AGREES ON GRADUAL
INTENSIFICATION THROUGH TAU 48 WITH A STEADY INTENSITY AFTERWARD.
MODELS RANGE FROM 40-50 KTS FROM TAUS 48-96. THE JTWC INTENSITY
FORECAST IS PLACED WITH MEDIUM CONFIDENCE, CLOSE TO THE MULTI-MODEL
CONSENSUS.

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