WDPN33 PGTW 132100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 08W (AMPIL) WARNING NR 
006//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 25.6N 139.5E
   INITIAL INTENSITY: 55 KTS
   GEOGRAPHIC REFERENCE: 582 NM SOUTH OF YOKOSUKA, JAPAN
   MOVEMENT PAST 6 HOURS: EAST-NORTHEASTWARD AT 04 KTS
   SIGNIFICANT WAVE HEIGHT: 21 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS A
CIRCULAR CENTRAL DENSE OVERCAST (CDO) OBSCURING THE LOW-LEVEL
CIRCULATION CENTER (LLCC). THE EXACT CENTER IS DIFFICULT TO LOCATE,
BUT A 131654Z AMSR-2 MICROWAVE IMAGE SHOWED IT TO BE BENEATH THE
NORTHERN HALF OF THE CDO. THIS MICROWAVE PASS ALSO REVEALED THAT
THE VORTEX TILT HAS CONTINUED TO PRECESS COUNTERCLOCKWISE AND
REDUCE IN MAGNITUDE, WITH THE MID-LEVEL CENTER NOW ABOUT 10 NM
SOUTHEAST OF THE LLCC. MODERATE NORTHERLY SHEAR IS EVIDENT, WITH
UPPER-LEVEL OUTFLOW RESTRICTED IN THE NORTHWEST QUADRANT. DEEP
CONVECTIVE BANDING IS NOTABLY LACKING FROM THE NORTHWESTERN
SEMICIRCLE IN THE AFOREMENTIONED MICROWAVE IMAGERY DUE TO THIS
SHEAR. THE INITIAL INTENSITY IS SET TO 55 KT BASED ON A BLEND OF
AGENCY DVORAK ESTIMATES AND OBJECTIVE SATELLITE INTENSITY
ESTIMATES.

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: T4.0 - 65 KTS
   RCTP: T2.5 - 35 KTS
   KNES: T3.5 - 55 KTS

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 15-20 KTS
   SST: 30-31 CELSIUS
   OUTFLOW: MODERATE EASTWARD

ANALYSIS CONFIDENCE:
   INITIAL POSITION: MEDIUM
   INITIAL INTENSITY: MEDIUM
   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 TO TRACK
NORTHEASTWARD WITHIN THE MONSOONAL SOUTHWESTERLY FLOW BELT. WITHIN
24 HOURS, A BEND TOWARDS THE NORTH IS EXPECTED, GUIDED BY A
DEEP-LAYER SUBTROPICAL RIDGE EAST OF JAPAN. THIS MOTION WILL CARRY
AMPIL CLOSE TO HONSHU BEFORE TURNING NORTHEASTWARD AROUND THE
NORTHERN FLANK OF THE RIDGE. DYNAMICAL MODELS ARE COMING INTO
BETTER AGREEMENT THROUGH 72 HOURS WITH TIGHTER SPREAD THAN 24 HOURS
AGO. THE JTWC TRACK FORECAST BRINGS AMPIL WITHIN APPROXIMATELY 25
NM OF CHOSHI, JAPAN, STAYING JUST OFFSHORE. HOWEVER, THE CURRENT
RANGE OF UNCERTAINTY KEEPS A POTENTIAL LANDFALL IN JAPAN ON THE
TABLE. TROPICAL STORM AMPIL IS ALSO LIKELY TO GROW IN SIZE AS IT
APPROACHES JAPAN, AND ITS WIND FIELD IS FORECAST TO OVERSPREAD A
PORTION OF EASTERN HONSHU EVEN AS THE CENTER PASSES OFFSHORE.
REGARDING THE INTENSITY FORECAST, ONGOING MODERATE SHEAR AND
ASSOCIATED DRY AIR ENTRAINMENT MAY LIMIT AMPIL DURING THE NEXT
24-36 HOURS, SO THE JTWC FORECAST MAINTAINS AN AVERAGE
INTENSIFICATION RATE DURING THAT PERIOD. AFTER 36 HOURS, WIND SHEAR
IS EXPECTED TO RELAX AS AN UPPER-LEVEL LOW NORTH OF THE STORM
DECAYS. IN A LOW-SHEAR ENVIRONMENT, TRACKING OVER 30-31 DEGREE
CELSIUS SEA SURFACE TEMPERATURES, AMPIL IS FORECAST TO RAPIDLY
INTENSIFY DURING THE 36-60 HOUR PERIOD AS IT APPROACHES JAPAN. THE
JTWC FORECAST SHOWS A PEAK INTENSITY OF 100 KT AT 48 HOURS, BUT
THIS PEAK COULD BE HIGHER THAN 100 KT BETWEEN THE 48 AND 72 HOUR
FORECAST POINTS. AFTER 72 HOURS, AMPIL WILL ACCELERATE
NORTHEASTWARD INTO THE MID-LATITUDE WESTERLIES, ULTIMATELY
UNDERGOING EXTRATROPICAL TRANSITION BY 120 HOURS.

MODEL DISCUSSION: THE JTWC TRACK FORECAST IS CLOSE TO THE
MULTI-MODEL CONSENSUS, AND A SMIDGE EAST (10-20 NM) OF THE PREVIOUS
FORECAST AROUND 72 HOURS. TRACK CONFIDENCE IS LOWER THAN AVERAGE
BEYOND 72 HOURS DUE TO VARIABILITY IN THE PREDICTED FORWARD SPEED
OF AMPIL AS THE STORM RECURVES INTO THE WESTERLIES. THE INTENSITY
GUIDANCE HAS A WIDE SPREAD DURING THE 48-72 HOUR PERIOD. THE JTWC
INTENSITY FORECAST IS CLOSE TO THE MULTI-MODEL CONSENSUS FOR THE
FIRST 36 HOURS, THEN HIGHER THAN CONSENSUS DURING THE 48-72 HOUR
PERIOD, LEANING TOWARDS THE DYNAMICAL MODELS AS OPPOSED TO THE
WEAKER STATISTICAL MODELS GIVEN THE ANTICIPATED FAVORABLE
ENVIRONMENT DURING THAT TIME.

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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