WDPN32 PGTW 092100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 25W (MAN-YI) WARNING NR 
004//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 16.0N 156.6E
   INITIAL INTENSITY: 45 KTS
   GEOGRAPHIC REFERENCE: 626 NM EAST OF SAIPAN
   MOVEMENT PAST 6 HOURS: NORTHWESTWARD AT 21 KTS
   SIGNIFICANT WAVE HEIGHT: 18 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY SHOWS INCREASING
CONVECTION OVER THE CORE OF MAN-YI WITH AN EXPANDING AREA OF
COOLING TOPS. WATER VAPOR ANIMATION SHOWS EXCELLENT OUTFLOW OVER
THE MAJORITY OF THE SYSTEM BUT THE EARLY SIGNS OF IMPINGEMENT ARE
BEGINNING TO SHOW OVER THE SOUTHWEST QUADRANT. THE ENVIRONMENT OVER
THE STORM IS DECENT BUT NOT HIGHLY FAVORABLE, WITH ONLY 10KTS OF
VERTICAL WINDSHEAR (VWS) DIRECTLY OVER THE LLCC.  THERE IS A SHARP VWS 
GRADIENT ALONG THE 20TH LATITUDE WITH PROHIBITIVE VWS POLEWARD OF THAT 
LINE. TOTAL PRECIPITABLE WATER LOOPS SHOW THERE IS PLENTY OF DEEP 
MOISTURE IN THE IMMEDIATE VICINTY OF THE STORM BUT DOWNSTREAM THERE 
ARE DRIER NORTHEASTERLIES. THE INTENSITY AT ANALYSIS TIME IS TWEAKED 
TOWARDS THE HIGH SIDE OF THE GUIDANCE BASED ON ADT RAW VALUES AND 
DMINT AS WELL AS THE RCTP DVORAK OF T3.0.

INITIAL WIND RADII BASIS: PERSISTENCE 

CURRENT STEERING MECHANISM: TS 25W IS LEAVING THE INFLUENCE OF THE
SOUTHWESTERN FLANK OF THE MAIN SUBTROPICAL RIDGE WHICH HAS SHIFTED
TO THE OTHER SIDE OF THE DATELINE AND THE SYSTEM IS NOW TRACKING 
THROUGH A WEAKNESS BETWEEN THAT RIDGE AND UPSTREAM RIDGE, WHICH IS 
ANCHORED IN AN ANTICYCLONE NEAR 20N 130E.  

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.0 - 30 KTS
   RJTD: T2.5 - 35 KTS
   RCTP: T3.0 - 45 KTS
   KNES: T2.0 - 30 KTS
   CIMSS SATCON: 40 KTS AT 1300Z
   CIMSS ADT: 43 KTS AT 091730Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE
   VWS: 10-15 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: MODERATE POLEWARD

ANALYSIS CONFIDENCE:
   INITIAL POSITION: MEDIUM
   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: THE NORTHWEST TRACK AND MODERATE
INTENSIFICATION WILL CONTINUE FOR THE NEXT 24 HOUS BEFORE TS 25W
GRADUALLY FLATTENS OUT AND BEGINS WEAKENING AS IT TRACKS OVER THE
NORTHERN ISLANDS OF CNMI. THE SYSTEM WILL SHOW ONLY LIMITED
EFFECTS ON SAIPAN. BEYOND THE MARIANAS THE PRIMARY STEERING
INFLUENCE WILL SHIFT TO THE EASTERNMOST EXTENSION OF THE
SUBTROPICAL RIDGE THAT EXTENDS FROM AN ANTICYCLONE OVER 20N 130E,
WHEREUPON VWS WILL INCREASE.  AT THE SAME TIME, DRIER
NORTHEASTERLIES WILL BEGIN FLOWING INTO THE NORTHWEST QUADRANT AND
EXACERBATE THE WEAKENING PROCESS.  VERTICAL CROSS SECTIONS FROM THE
HAFS-A MODEL INDICATE THE INCREASED SHEAR WILL BE MOST PRONOUNCED
IN THE MID-LEVELS. THE NEXT 24 HOURS WILL BE THE FUN AND
INTERESTING PERIOD, FOLLOWED BY A SLOW AND STEADY DEATH DUE TO
INCREASING VWS AND DRY AIR ENTRAINMENT. WHILE IT IS NEVER A 
COMFORTABLE FEELING FORECASTING DISSIPATION OVER THE PHILIPPINE SEA, 
THE GUIDANCE IS EMPHATIC AND UNANIMOUS ABOUT THE DECAY. WINTER IS 
COMING. 

MODEL DISCUSSION: TRACK GUIDANCE IS TIGHT LENDING GOOD CONFIDENCE
TO THE TRACK FORECAST. INTENSITY GUIDANCE IS ALSO CONSISTENT IN THE 
DECAY OF THE STORM. 


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