WDPN33 PGTW 172100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 08W (AMPIL) WARNING NR 
023//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 39.5N 152.5E
   INITIAL INTENSITY: 60 KTS
   GEOGRAPHIC REFERENCE: 522 NM EAST OF MISAWA, JAPAN
   MOVEMENT PAST 6 HOURS: EAST-NORTHEASTWARD AT 23 KTS
   SIGNIFICANT WAVE HEIGHT: 25 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS TROPICAL
STORM 08W (AMPIL) AS BEGINNING TO UNDERGO EXTRA-TROPICAL TRANSITION
AS ANY LAST REMAINING CONVECTIVE STRUCTURES HAVE NOW DISSIPATED
OVER THE LAST SIX HOURS, AND THE REMNANT CIRRUS SHIELD HAS
PROGRESSED EASTWARD AND POLEWARD OF THE LOW-LEVEL CIRCULATION
CENTER (LLCC). THE SYSTEM CONTINUES TO RAPIDLY WEAKEN WHILE THE
CENTRAL CORE SLOWLY BECOMES INCREASINGLY TILTED WITH THE SUSTAINED
IMPACT OF STRONG VERTICAL WIND SHEAR (VWS) BETWEEN 25-30 KTS, AND
DRY-AIR STEADILY WRAPS CYCLONICALLY INTO THE LLCC FROM THE WEST AS
AN INCREASING STRATOCUMULUS FIELD GROWS THROUGHOUT THE WESTERN
PERIPHERY OF THE CIRCULATION. A 172048Z WSFM 89 GHZ MICROWAVE PASS
HAS CONFIRMED THE RAPID WEAKENING OF THE SYSTEM WITH AN ABSENCE OF
SUPPORTIVE CONVECTIVE FEATURES AND INCREASING VERTICAL TILT IN TS
08W. THE INITIAL POSITION IS PLACED WITH MEDIUM CONFIDENCE AS THE
LLCC HAS BECOME PARTIALLY EXPOSED OVER THE LAST FEW HOURS ON
ANIMATED MSI. THE INITIAL INTENSITY IS ASSESSED WITH LOW CONFIDENCE
BASED ON THE CONTINUED WIDE RANGE OF INTENSITIES ON AGENCY FIX
ESTIMATES AND OBJECTIVE INTENSITY ESTIMATES LISTED BELOW.

INITIAL WIND RADII BASIS: PERSISTENCE 

CURRENT STEERING MECHANISM: NORTHWESTERN PERIPHERY OF A DEEP-LAYER
SUBTROPICAL RIDGE (STR) TO THE SOUTHEAST. 

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T3.0 - 45 KTS
   RJTD: T3.0 - 45 KTS
   RCTP: T3.5 - 55 KTS
   KNES: T2.5 - 35 KTS
   CIMSS SATCON: 66 KTS AT 0000Z
   CIMSS ADT: 35 KTS AT 0000Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: UNFAVORABLE
   VWS: 25-30 KTS
   SST: 24-26 CELSIUS
   OUTFLOW: MODERATE POLEWARD AND EQUATORWARD

ANALYSIS CONFIDENCE:
   INITIAL POSITION: MEDIUM
   INITIAL INTENSITY: LOW
   INITIAL WIND RADII: MEDIUM

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: THERE ARE NO SIGNIFICANT CHANGES TO
THE FORECAST FROM THE PREVIOUS WARNING.

FORECAST DISCUSSION: TS 08W IS EXPECTED TO CONTINUE TRACKING
NORTHEASTWARD ALONG THE NORTHWESTERN EDGE OF THE DEEP-LAYER
SUBTROPICAL RIDGE. OVER THE NEXT 24 HOURS, A MAJOR SHORTWAVE TROUGH
ASSOCIATED WITH THE MID-LATITUDE LONGWAVE PATTERN WILL FURTHER
ENHANCE THE SYSTEMS NORTHEAST TRACK SPEED, BECOMING COMPLETELY
EXTRA-TROPICAL AS SEA SURFACE TEMPERATURES DECREASE TO BELOW 20 C
AND VWS INCREASES ABOVE 35 KTS. THE SYSTEM IS EXPECTED TO RAPIDLY
WEAKEN TO 40 KTS BY TAU 36, AND INTERACTION WITH THE MID-LATITUDES
WILL PREVENT ANY OPPORTUNITY FOR REGENERATION.

MODEL DISCUSSION: MODEL GUIDANCE IS IN VERY TIGHT AGREEMENT,
DEPICTING A CROSS-TRACK SPREAD OF ONLY 50 NM BY THE END OF THE
FORECAST PERIOD. THE JTWC FORECAST IS PLACED WITHIN THE GUIDANCE
ENVELOPE WITH VERY HIGH CONFIDENCE. INTENSITY GUIDANCE IS ALSO IN
GOOD AGREEMENT, WITH CONSENSUS MEMBERS ILLUSTRATING THAT TS 08W
WILL CONTINUE TO QUICKLY WEAKEN AND BECOME EXTRA-TROPICAL BETWEEN
TAU 24 AND TAU 36, LENDING MEDIUM CONFIDENCE TO THE JTWC FORECAST.

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