WDPN32 PGTW 102100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 25W (MAN-YI) WARNING NR 
008//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 15.2N 153.9E
   INITIAL INTENSITY: 40 KTS
   GEOGRAPHIC REFERENCE: 469 NM EAST OF SAIPAN
   MOVEMENT PAST 6 HOURS: SOUTHWESTWARD AT 09 KTS
   SIGNIFICANT WAVE HEIGHT: 16 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
TROPICAL STORM 25W (MAN-YI) HAS PEAKED AND BEGAN BENDING INTO A
SOUTHWESTWARD TRACK.  ANIMATED WATER VAPOR AND INFRARED IMAGERY
SHOWING THE BULK OF THE CONVECTIVE MASS PUSHING VIGOROUSLY
SOUTHWARD IS DECEPTIVE. THE LOW-LEVEL CIRCULATION CENTER REMAINS
ACTIVE TO THE NORTHWEST, AT THE LEADING EDGE OF NEWLY FORMING BURST
OF CONVECTION. THE SYSTEM HAS, HOWEVER, BEGUN A TERMINAL DOWNTREND
AS EXPECTED. THE WATER VAPOR ALSO REVEALS ANOTHER FOREBODING
SIGN--A GAPING DEARTH OF DEEP MOISTURE BETWEEN THE STORM AND THE
140TH MERIDIAN. THE CURRENT INTENSITY ASSESSMENT OF 40KTS MAY BE A
LITTLE ON THE GENEROUS SIDE, BUT AGENCY SUBJECTIVE DVORAKS RANGE
FROM 35 TO 45 KNOTS AND CIMSS OBJECTIVE INTENSITY ASSESSMENTS RANGE
FROM 35 TO 40KTS. THE SYSTEM IS SEEING THE LAST OF ITS BEST
ENVIRONMENT AND TRACKING TOWARDS A MORE HOSTILE ENVIRONMENT
CHARACTERIZED BY DRIER AIR AND HIGHER VERTICAL WIND SHEAR. TOTAL
PRECIPITABLE WATER LOOPS REVEAL A DRY STREAK WRAPPING ALONG THE
SOUTHWEST QUADRANT AND HEADING TOWARDS THE CORE. TS 25W IS COMING
UNDER THE INFLUENCE OF A MAJOR STEERING RIDGE EXTENDING FROM AN
ANTICYCLONE NEAR 19N 120E. THE RIDGE HAS SHIFTED ABOUT A DEGREE
EQUATORWARD DURING THE PAST 24 HOURS.

INITIAL WIND RADII BASIS: PERSISTENCE WITH A RADII TAPERED DOWN A
STEP IN COINCIDENCE WITH THE FALLING INTENSITY. 

CURRENT STEERING MECHANISM: THE EASTERN FLANK OF THE SUBTROPICAL
RIDGE EXTENDING ALONG THE 19TH LATITUDE.

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T3.0 - 45 KTS
   RJTD: T2.5 - 35 KTS
   RCTP: T3.0 - 45 KTS
   KNES: T3.0 - 45 KTS
   CIMSS SATCON: 47 KTS AT 1300Z
   CIMSS ADT: 37 KTS AT 101730Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: UNFAVORABLE
   VWS: 19 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: MODERATE POLEWARD

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

3. FORECAST REASONING.

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

FORECAST DISCUSSION: ALTHOUGH THE FORECAST PHILOSOPHY AND OVERALL
STORY HAS NOT CHANGED, A BUILDING UPSTREAM STEERING RIDGE HAS
FORCED THE TRACK FURTHER SOUTH, INCREASING THE THREAT TO SAIPAN AND
TINIAN. 24 HOURS AGO, THE TRACK WAS WELL NORTH OF SAIPAN BUT
GRADUALLY IT HAS WALKED EQUATORWARD, INCREASING THE PROBABILITY OF
SMALL CRAFT TO NEAR GALE FORCE WINDS OVER BOTH ISLANDS. AS THE FAR
EASTERN EXTENSION OF THE SUBTROPICAL RIDGE HAS PUSHED OVER THE
SYSTEM RESULTED IN A SHORT-TERM JOG TO THE SOUTHWEST BUT GUIDANCE
IS IN GOOD ALIGNMENT THAT THE SYSTEM WILL RETURN TO A NEAR WESTERLY
TRACK ONCE IT SETTLES UNDER THE RIDGE.  THE WEAKENING TREND IS WELL
UNDERWAY, HOWEVER, AND THE SYSTEM HAS ENTERED A SLOW AND STEADY
DECLINE PHASE DUE TO DRY AIR ENTRAINMENT AND INCREASING VERTICAL
WIND SHEAR.  A 96 HOUR POSITION HAS BEEN ADDED BACK TO THE TRACK
FORECAST DUE TO EXTREMELY LONG-RANGE GUIDANCE INDICATING THE
POSSIBILITY OF REGENERATION IN THE PHILIPPINE SEA NORTH OF THE
PALAU-YAP REGION. A DISSIPATION OVER WATER SCENARIO IN THE
PHILIPPINE SEA IS UNCOMMON, BUT IT DOES HAPPEN.  A KEY INDICATOR OF
THE LIKELIHOOD OR NON-LIKELIHOOD OF REGENERATION WILL BE THE
INTENSITY OF THE SYSTEM AS IT CROSSES TINIAN. 

MODEL DISCUSSION: TRACK GUIDANCE IS UNANIMOUS IN SHOWING A RETURN
FROM THE CURRENT SOUTHWEST LEG TO A WESTWARD TRACK.  THE
CROSS-TRACK SPREAD BETWEEN MODELS AND ENSEMBLES IS WIDER THAN
AVERAGE DUE TO POLEWARD OUTLIERS WHICH ARE READILY DISMISSED. THE
JTWC TRACK FORECAST SHADES EQUATORWARD OF CONSENSUS WHILE THE
INTENSITY FORECAST STAYS CLOSER TO THE HAFS-A OUTPUT BUT STILL
FOLLOWS THE SAME TREND AS THE INTENSITY CONSENSUS. 

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