WDPN33 PGTW 131500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 08W (AMPIL) WARNING NR 
005//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 25.5N 138.9E
   INITIAL INTENSITY: 55 KTS
   GEOGRAPHIC REFERENCE: 589 NM SOUTH OF YOKOSUKA, JAPAN
   MOVEMENT PAST 6 HOURS: NORTHEASTWARD AT 05 KTS
   SIGNIFICANT WAVE HEIGHT: 18 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS AN LLCC
FULLY OBSCURED BY THE DEVELOPING CDO FEATURE AND CLEARLY VISIBLE
SPIRAL BANDS OF DEEP CONVECTION TO THE NORTHEAST AND SOUTHEAST OF
THE SYSTEM. SUBSEQUENT EIR IMAGERY SUGGESTS THE CLOUD TOPS ARE
ALREADY STARTING TO WARM A BIT AND THAT THE FLARE UP OF CONVECTION
MAY BE SHORT-LIVED. A 131136Z ASCAT-B BULLSEYE PASS SHOWED A
WELL-DEFINED LLCC HIDING BENEATH THE CDO AND PROVIDING HIGH
CONFIDENCE TO THE INITIAL POSITION ASSESSMENT. THE INITIAL
INTENSITY OF 55 KTS IS ASSESSED WITH HIGH CONFIDENCE BASED ON THE
AFOREMENTIONED SCATTEROMETER PASS AND GOOD AGREEMENT AMONG AGENCY
SUBJECTIVE INTENSITY ESTIMATES, AS WELL AS OBJECTIVE ESTIMATES. THE
ENVIRONMENT REMAINS MOSTLY FAVORABLE WITH HIGH SSTS, AND LOW
VERTICAL WIND SHEAR OFFSET SLIGHTLY BY WEAK UPPER-LEVEL OUTFLOW,
PRIMARILY EQUATORWARD. ANIMATED WATER VAPOR IMAGERY, AS WELL AS THE
CIMSS ATMOSPHERIC MOTION VECTOR (AMV) ANALYSIS REVEALS AN
UPPER-LEVEL MESOSCALE ANTICYCLONE POSITIONED JUST NORTHWEST OF THE
SYSTEM, WHICH IS APPLYING SOME PRESSURE AND WESTERLY SHEAR UPON TS
08W, HINDERING POLEWARD OUTFLOW AND LIMITING DEVELOPMENT POTENTIAL
IN THE NEAR-TERM.

INITIAL WIND RADII BASIS: SCATTEROMETER DATA 

CURRENT STEERING MECHANISM: NEAR-EQUATORIAL RIDGE TO THE SOUTHEAST

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T3.5 - 55 KTS
   RJTD: T3.5 - 55 KTS
   KNES: T3.5 - 55 KTS
   CIMSS SATCON: 42 KTS AT 131200Z
   CIMSS ADT: 49 KTS AT 131200Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 5-10 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: MODERATE EQUATORWARD

ANALYSIS CONFIDENCE:
   INITIAL POSITION: HIGH
   INITIAL INTENSITY: HIGH
   INITIAL WIND RADII: HIGH

3. FORECAST REASONING.

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

FORECAST DISCUSSION: TROPICAL STORM 08W (AMPIL) CONTINUES TRACKING
NORTHEASTWARD DUE TO THE STEERING FROM A NEAR-EQUATORIAL RIDGE
(NER) TO THE SOUTH AND SOUTHEAST OF THE STORM. WITHIN THE NEXT 30
HOURS HOWEVER, THE NER WILL CONNECT WITH A STRONG STR CURRENTLY
LOCATED AROUND 40N AND THE LATTER WILL BECOME THE PRIMARY STEERING
INFLUENCE FOR TS 08W, AS THE OTHER STORM - TD 09W - CONTINUES
TRACKING NORTHEAST. IN RESPONSE, TS 08W WILL TURN DUE NORTH AROUND
TAU 30. AS TS AMPIL REACHES THE AXIS OF THE STR BY APPROXIMATELY
TAU 66, IT WILL BE STEERED NORTHEASTWARD, ALONG THE NORTHWESTERN
SIDE OF THE RIDGE, AND CONTINUE ON THAT PATH UNTIL THE END OF THE
FORECAST PERIOD. AS WITH THE PREVIOUS FORECAST DISCUSSION, THE
TIMING OF THIS INTERACTION WILL DETERMINE HOW CLOSE THE CPA OF THE
TS AMPIL WILL BE TO THE MAINLAND JAPAN AND TOKYO AREA. IN TERMS OF
INTENSITY FORECAST, SYSTEM IS EXPECTED TO CONTINUE TO INTENSIFY
SLOWLY THROUGH TAU 12, AS MAJORITY OF THE ENVIRONMENTAL CONDITIONS
ARE FAVORABLE, BUT FURTHER RAPID DEVELOPMENT IS HINDERED BY THE
INFLUX OF DRY AIR FROM THE WEST AROUND TAU 18. FOLLOWING TAU 24,
WITH NO MORE DRY AIR INJECTION, THE MAJORITY OF THE CONDITIONS WILL
BECOME HIGHLY FAVORABLE, WITH DEVELOPMENT OF AN UPPER-LEVEL
ANTICYCLONE OVER TOP OF THE SYSTEM, ENHANCED BY POLEWARD OUTFLOW
INTO THE EASTERN SIDE OF AN UPPER-LEVEL LOW POSITIONED TO THE
NORTH. AS THIS OCCURS WHILE THE SYSTEM PASSES OVER A REGION OF
ANOMALOUSLY HIGH SEA SURFACE TEMPERATURES, THE PROBABILITY OF RAPID
INTENSIFICATION IS HIGH. TS 08W IS CURRENTLY FORECASTED TO REACH
ITS MAXIMUM INTENSITY OF APPROXIMATELY 105 KNOTS BY TAU 60 - NOT
DEPICTED ON THE FORECAST GRAPHIC DUE TO TIME STEP LIMITATIONS, AS
IT APPROACHES THE CHIBA PENINSULA. AFTER CPA TO JAPAN, THE SYSTEM
WILL BEGIN A STEADY AND FAIRLY RAPID WEAKENING TREND AS IT
ENCOUNTERS COOLER SSTS, INCREASING SHEAR AND BEGINS EXTRATROPICAL
TRANSITION. AS NOTED IN THE PRIOR DISCUSSION, THE CURRENT CPA TO
JAPAN FALLS BETWEEN TWO TAUS AND THEREFORE THE ACTUAL CPA MAY FALL
CLOSER TO MAINLAND JAPAN THAN DEPICTED BY THE TRACK INTERPOLATION. 

MODEL DISCUSSION: NUMERICAL PREDICTION MODEL GUIDANCE REMAINS IN
GOOD AGREEMENT WITH THE CROSS-TRACK SPREAD OF 110 NM AND
ALONG-TRACK SPREAD OF 192 NM AT TAU 72, WITH ALONG-TRACK OUTLIERS
OF JGSM AND ECMWF, INDICATING A FASTER TRACK SPEED THAN THE
REMAINDER OF THE CONSENSUS MEMBERS. OVERALL, THE GUIDANCE ENVELOPE
HAS TIGHTENED UP ON A TRAJECTORY THAT SKIRTS THE EASTERN SIDE OF
THE CHIBA PENINSULA. ENSEMBLE MODELS (ECENS AND GEFS) HAVE ALSO
SHOWN DECREASED CROSS-TRACK SPREAD AND INTER-MODEL AGREEMENT,
LENDING INCREASED CONFIDENCE TO THE OVERALL TRACK FORECAST.
ALONG-TRACK SPREAD INCREASES SIGNIFICANTLY AFTER THE SYSTEM TURNS
NORTHEAST AND BEGINS EXTRATROPICAL TRANSITION. THE JTWC TRACK
FORECAST IS LAID CLOSE TO THE MULTI-MODEL CONSENSUS WITH MEDIUM
CONFIDENCE THROUGH TAU 72. INTENSITY GUIDANCE REMAINS CONSISTENT
RUN TO RUN, ALLOWING FOR SLOWER INTENSITY DEVELOPMENT WITHIN THE
NEXT 36 HOURS, FOLLOWED BY RAPID INTENSIFICATION BETWEEN TAUS 36
AND 60. THE RI PORTION OF THE FORECAST IS APPROXIMATELY 10 KTS
HIGHER THAN CONSENSUS, BUT 15 KTS LESS THAN COAMPS-TC ENSEMBLE,
WHICH IS CURRENTLY CALLING FOR HIGHEST PEAK INTENSITY OF 120 KNOTS.


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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