WDPN31 PGTW 131500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 28W (YAMANEKO) WARNING 
NR 005//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 22.3N 165.7E
   INITIAL INTENSITY: 35 KTS
   GEOGRAPHIC REFERENCE: 187 NM NORTH-NORTHWEST OF WAKE ISLAND
   MOVEMENT PAST 6 HOURS: NORTHWARD AT 02 KTS
   SIGNIFICANT WAVE HEIGHT: 14 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY CURRENTLY
DEPICTS AN ASYMMETRIC SYSTEM THAT CONTINUES TO BATTLE HIGH VERTICAL
WIND SHEAR (VWS), AS THE LOW LEVEL CIRCULATION CENTER (LLCC) IS
FULLY EXPOSED. AN EARLIER 130716Z SSMIS 91GHZ MICROWAVE IMAGE
DEPICTS A SHEARED ENVIRONMENT AND REVEALS A BROAD LLCC POSITIONED
ALONG THE SOUTHWESTERN EDGE OF A CURVED CONVECTIVE BAND. THE INITIAL
POSITION IS PLACED WITH HIGH CONFIDENCE BASED ON THE EIR LOOP WHICH 
SHOWS THE DEFINED SLIGHTLY ELONGATED LLCC TO THE SOUTHWEST OF THE
CONVECTIVE MASS, ALONG WITH THE SSMIS 91GHZ MICROWAVE IMAGE
DESCRIBED ABOVE. THE INITIAL INTENSITY REMAINS SET AT 35 KNOTS,
SLIGHTLY BELOW THE PGTW AND KNES AGENCY DVORAK INTENSITY ESTIMATES
AND CLOSER TO THE ADT OBJECTIVE INTENSITY ESTIMATE OF 34 KNOTS.
ENVIRONMENTAL ANALYSIS INDICATES MARGINALLY UNFAVORABLE CONDITIONS,
WITH STRONG POLEWARD OUTFLOW ALOFT, ALONG WITH WARM (27-28C) SEA
SURFACE TEMPERATURES (SSTS), OFFSET BY STRONG (30KT) VERTICAL WIND
SHEAR (VWS).

INITIAL WIND RADII BASIS: PERSISTENCE 

CURRENT STEERING MECHANISM: STRONG TRANSITORY RIDGE TO THE NORTH
AND WEAKER SUBTROPICAL RIDGE
(STR) TO THE EAST. 

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T3.0 - 45 KTS
   RJTD: T2.0 - 30 KTS
   KNES: T3.0 - 45 KTS
   PHFO: T3.0 - 45 KTS
   CIMSS ADT: 34 KTS AT 131240Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY
UNFAVORABLE
   VWS: 30+ KTS
   SST: 27-28 CELSIUS
   OUTFLOW: STRONG POLEWARD

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

3. FORECAST REASONING.

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

FORECAST DISCUSSION: TROPICAL STORM 28W (YAMANEKO) CONTINUES TO
MOVE NORTHWARD AT A RELATIVELY SLOW PACE, DUE TO A SHALLOW
TRANSITORY RIDGE POSITIONED NORTH OF THE SYSTEM NEAR 37N 168E.
HOWEVER, TRACK MOTION IS EXPECTED TO ACCELERATE POLEWARD
DRAMATICALLY OVER THE NEXT 12 HOURS, AS THE TRANSITORY RIDGE IS
EXPECTED TO MOVE EASTWARD AND REORIENT TO A MORE MERIDONAL STATE.
BY TAU 24, THE SYSTEM WILL TURN AND TRANSIT IN A NORTHEASTWARD
DIRECTION AS AN APPROACHING NEGATIVELY TILTED UPPER-LEVEL TROUGH IS
EXPECTED TO INTERACT WITH THE SYSTEM.  THE TRACK SPEED IS FORECAST
TO CONTINUE TO ACCELERATE WHILE THE SYSTEM MAINTAINS A
NORTHEASTWARD DIRECTION THROUGHOUT THE FORECAST PERIOD. TS 28W
CONTINUES TO MAINTAIN A CURRENT INTENSITY OF 35 KNOTS EVEN IN THE
FACE OF MARGINALLY UNFAVORABLE ENVIRONMENT CONDITIONS WITH HIGH
SHEAR. HOWEVER, THE SYSTEM CONTINUES TO HAVE ACCESS TO STRONG
POLEWARD OUTFLOW WHICH IS HELPING TO OFFSET THE HIGH SHEAR,
ALLOWING FOR THE SYSTEM TO MAINTAIN TS STRENGTH THROUGH THE END OF
THE FORECAST. THE SYSTEM IS FORECAST TO INTERACT WITH THE
NEGATIVELY TILTED TROUGH WHICH IS RESULT IN SUBTROPICAL TRANSITION
BY TAU 12, BEFORE QUICKLY PERFORMING EXTRATROPICAL TRANSITION (ETT)
WHILE TRANSFORMING INTO A GALE-FORCE LOW PRESSURE SYSTEM WITH AN
EXPANDING WIND FIELD BETWEEN TAU 24 AND TAU 36. ADDITIONAL
INTENSIFICATION IS POSSIBLE AFTER ETT AND BEYOND THE FORECAST AS
THE SYSTEM TRANSITS TOWARD THE ALEUTIAN ISLANDS.  

MODEL DISCUSSION: NUMERICAL MODEL DETERMINISTIC AND ENSEMBLE TRACK
GUIDANCE ARE IN GOOD AGREEMENT THROUGH OUT THE FORECAST PERIOD,
WITH MINIMAL CROSS-TRACK SPREAD OUT TO 170NM BY TAU 36. THEREFORE,
THE JTWC TRACK FORECAST IS PLACED WITH HIGH CONFIDENCE AND REMAINS
CONSISTENT WITH THE PREVIOUS ONE. INTENSITY GUIDANCE IS IN FAIR
AGREEMENT, WITH THE HWRF STILL INDICATING A PEAK OF 40-45 KTS
WITHIN THE NEXT 12 HOURS, WHILE DECAY SHIPS SHOWS A QUICK DROP OFF
INTENSITY, WHILE ALL INTENSITY MODELS SHOW INTENSIFICATION BEYOND
THE FORECAST AFTER ETT. FOR THESE REASONS THE JTWC INTENSITY
FORECAST IS PLACED WITH MEDIUM CONFIDENCE AND REMAINS CONSISTENT
WITH THE PREVIOUS FORECAST, WHILE FOLLOWING CLOSE TO THE
MULTI-MODEL CONSENSUS. 

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