WDPN32 PGTW 250300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 11W (SHANSHAN) WARNING NR 015//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 25.0N 138.9E
   INITIAL INTENSITY: 65 KTS
   GEOGRAPHIC REFERENCE: 131 NM WEST OF IWO TO
   MOVEMENT PAST 6 HOURS: NORTHWESTWARD AT 13 KTS
   SIGNIFICANT WAVE HEIGHT: 26 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS A DIMPLE
DEVELOPING IN THE CENTER OF DEEP CONVECTION OBSCURING THE LOW-LEVEL
CIRCULATION CENTER (LLCC) OF TYPHOON 11W. ON WATER VAPOR IMAGERY,
OUTFLOW APPEARS TO BE PULLED NORTHWESTWARD RATHER THAN STRICTLY
POLEWARD AS THE TROPICAL UPPER TROPOSPHERIC TROUGH (TUTT) CELL TO
THE NORTHWEST DRIFTS WESTWARD. THE CONVECTION HAS BECOME MORE
SYMMETRIC OVER THE LAST 12 HOURS AS THE SHEAR HAS DECREASED BUT
REMAINED MODERATE (10-15KTS). A 242135Z F-17 SSMIS 91GHZ IMAGE
DEPICTS A MICROWAVE EYE FEATURE WITH THE DEEPEST CONVECTION LOCATED
TO THE SOUTHWEST. THE INITIAL INTENSITY OF 65 KTS IS ASSESSED WITH
HIGH CONFIDENCE BASED ON THE AFOREMENTIONED ANIMATED MSI. THE
INITIAL INTENSITY OF 65 KTS IS ASSESSED WITH MEDIUM CONFIDENCE
BASED ON THE AGENCY AND OBJECTIVE FIXES LISTED BELOW.

INITIAL WIND RADII BASIS: OBJECTIVE BEST TRACK 

CURRENT STEERING MECHANISM: ON THE SOUTHWESTERN PERIPHERY OF A
SUBTROPICAL RIDGE (STR) TO THE NORTHEAST

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T4.5 - 77 KTS
   RJTD: T4.0 - 65 KTS
   RCTP: T4.0 - 65 KTS
   KNES: T4.0 - 65 KTS
   CIMSS SATCON: 59 KTS AT 0100Z
   CIMSS ADT: 53 KTS AT 242330Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 10-15 KTS
   SST: 30-31 CELSIUS
   OUTFLOW: STRONG POLEWARD

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

3. FORECAST REASONING.

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

FORECAST DISCUSSION: TYPHOON (TY) 11W WILL CONTINUE TRACKING
NORTHWESTWARD OVER THE NEXT 48 HOURS BEFORE ROUNDING THE RIDGE AND
ENDING ON A NORTHEASTWARD TRACK THROUGH THE END OF THE FORECAST
PERIOD. AS THE TUTT CELL DRIFTS WESTWARD AWAY FROM THE CIRCULATION,
THE VERTICAL WIND SHEAR (VWS) WILL CONTINUE TO DECREASE AND ALLOW
FOR FURTHER INTENSIFICATION WITH A PEAK OF 110KTS BY TAU 48.
BETWEEN TAU 48 AND 72, THE SYSTEM WILL START TO INTERACT WITH AN
UPPER-LEVEL TROUGH, CAUSING THE SYSTEM TO INITIATE EXTRATROPICAL
TRANSITION (ETT). QUICKLY AFTER TAU 72, TY 11W WILL MAKE LANDFALL
AND INTERACT WITH THE MOUNTAINOUS TOPOGRAPHY OF JAPAN. THE SYSTEM
WILL CONTINUE TO BECOME BAROCLINIC AS IT COMES OUT OVER WATER
BETWEEN TAU 72 AND 96, AND TRACK OVER COOL SEA SURFACE TEMPERATURES
BETWEEN TAU 96 AND 72 (BELOW 26C). THE SYSTEM WILL BECOME FULLY
FRONTAL AND BAROCLINIC BY TAU 120 WHEN IT IS FINALLY DESIGNATED AS
EXTRATROPICAL.

MODEL DISCUSSION: DETERMINISTIC MODEL GUIDANCE IS IN GOOD AGREEMENT
FOR THE FIRST 72 HOURS OF THE JTWC TRACK WITH A MAXIMUM TRACK
SPREAD OF 100NM BY TAU 72. THE CONFIDENCE IS LOW IN THE LATE-TERM
FORECAST BEYOND TAU 72 AS THE SPREAD OPENS TO 440NM BASED ON VARIED
INTERPRETATIONS OF INTERACTION WITH THE STR TO THE NORTHEAST. GFS
MAINTAINS A NORTH-NORTHEASTWARD TRACK AFTER ROUNDING THE RIDGE
WHILE NAVGEM MAINTAINS A NORTHEASTWARD TRACK. THE JTWC INTENSITY
GUIDANCE REFLECTS THE UNCERTAINTY IN TRACK GUIDANCE AS THE
INTENSITIES SHOW A SPREAD OF 80KTS. GFS REPRESENTS THE HIGHEST
INTENSITY BASED ON THE STANDOUT NORTH-NORTHEASTWARD TRACK WHILE THE
BULK OF THE OTHER GUIDANCE IS BETWEEN 105-125. THE JTWC INTENSITY
GUIDANCE LIES CLOSELY TO THE CONSENSUS MEAN WITH A PEAK OF 110KTS
AT TAU 48.

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