WDPS32 PGTW 070900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 11P (ELEVEN) WARNING NR 
003//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 15.6S 166.8W
   INITIAL INTENSITY: 40 KTS
   GEOGRAPHIC REFERENCE: 239 NM EAST-SOUTHEAST OF PAGO PAGO,
AMERICAN SAMOA
   MOVEMENT PAST 6 HOURS: SOUTHEASTWARD AT 23 KTS
   SIGNIFICANT WAVE HEIGHT: 20 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) SHOWS A
MIDGET-SIZED SYSTEM TRACKING AWAY FROM AMERICAN SAMOA WITH SHALLOW 
RAIN BANDS FEEDING INTO THE LOW LEVEL CIRCULATION (LLC) THAT IS 
OBSCURED BY A COLD DENSE OVERCAST THAT HAS DEEPENED SLIGHTLY IN THE 
LAST SIX HOURS. THE INITIAL POSITION IS PLACED WITH HIGH CONFIDENCE 
BASED ON A DEFINED LLC FEATURE IN THE 070549Z SSMIS MICROWAVE IMAGE. 
THE INITIAL INTENSITY IS PLACED WITH MEDIUM CONFIDENCE BASED ON THE 
HIGH END OF AGENCY AND AUTOMATED DVORAK ESTIMATES AND REFLECTS THE 
SLIGHT CONVECTIVE IMPROVEMENT. ANALYSIS INDICATES A MARGINALLY 
FAVORABLE ENVIRONMENT WITH WARM SST AND STRONG POLEWARD OUTFLOW OFFSET 
BY MODERATE-HIGH VWS.

INITIAL WIND RADII BASIS: PERSISTENCE.

CURRENT STEERING MECHANISM: NEAR EQUATORIAL RIDGE (NER) EXTENSION
TO THE NORTHEAST.

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.5 - 35 KTS
   CIMSS SATCON: 44 KTS AT 070310Z
   CIMSS ADT: 43 KTS AT 070540Z
   CIMSS AIDT: 32 KTS AT 070540Z
   CIMSS DPRINT: 41 KTS AT 070500Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE
   VWS: 20-25 KTS
   SST: 30-31 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: TC 11P WILL CONTINUE SOUTHEASTWARD UNDER THE
STEERING NER UP TO TAU 24. AFTERWARD, A SUBTROPICAL RIDGE (STR) TO
THE SOUTH WILL BLOCK ITS FORWARD MOTION AND COMPETE FOR STEERING.
THE MARGINALLY FAVORABLE ENVIRONMENT WILL SUSTAIN THE CURRENT
INTENSITY UP TO TAU 12; AFTERWARD, INCREASING VWS WILL MOSTLY BE
RESPONSIBLE FOR ITS GRADUAL DECAY, LEADING TO DISSIPATION BY TAU
36. 

MODEL DISCUSSION: NUMERICAL MODELS ARE IN GOOD AGREEMENT WITH AN
EVEN SPREAD TO 114NM BY TAU 24. AFTERWARD, A WESTWARD AND EASTWARD
TRACK BIFURCATION SCENARIO ENSUES WITH THE STR AND THE NER
COMPETING FOR STEERING. IN VIEW OF THIS, THERE IS ONLY MEDIUM
CONFIDENCE IN THE JTWC TRACK AND INTENSITY FORECASTS. 

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