WDPS31 PGTW 070900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 10P (NAT) WARNING NR 
006//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 18.7S 152.7W
   INITIAL INTENSITY: 35 KTS
   GEOGRAPHIC REFERENCE: 191 NM WEST-SOUTHWEST OF PAPEETE, TAHITI
   MOVEMENT PAST 6 HOURS: EAST-SOUTHEASTWARD AT 13 KTS
   SIGNIFICANT WAVE HEIGHT: 18 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) SHOWS A MEDIUM-SIZED
SYSTEM WITH NO SIGNIFICANT FEEDER BANDS TRACKING SOUTH OF THE
FRENCH POLYNESIAN ISLANDS. THE LOW LEVEL CIRCULATION (LLC) IS
PARTLY EXPOSED WITH THE MAIN CONVECTION SHEARED EASTWARD. THE
INITIAL POSITION IS PLACED WITH MEDIUM CONFIDENCE BASED ON A RAGGED
LLC FEATURE IN THE 070409Z SSMIS MICROWAVE IMAGE. THE INITIAL
INTENSITY IS PLACED WITH MEDIUM CONFIDENCE BASED ON OVERALL
ASSESSMENT OF AGENCY AND AUTOMATED DVORAK ESTIMATES. ANALYSIS
INDICATES A MARGINAL ENVIRONMENT WITH WARM SST AND STRONG POLEWARD
OUTFLOW OFFSET BY HIGH VWS AND DRY AIR ENTRAINMENT AT THE LOW
LEVELS.

INITIAL WIND RADII BASIS: PERSISTENCE. 

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

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.5 - 35 KTS
   CIMSS ADT: 33 KTS AT 070540Z
   CIMSS AIDT: 35 KTS AT 070540Z
   CIMSS DPRINT: 35 KTS AT 070600Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINAL
   VWS: 25-30 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: STRONG POLEWARD
   OTHER FACTORS: DRY AIR ENTRAINMENT.

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: TC NAT WILL CONTINUE WESTWARD UNDER THE
STEERING INFLUENCE OF THE NER TO THE NORTH. THE MARGINAL
ENVIRONMENT WILL SUSTAIN THE CURRENT INTENSITY AT BEST BEFORE VWS
AND DRY AIR ENTRAINMENT WILL DOMINATE AND DISSIPATE THE SYSTEM BY
TAU 36, POSSIBLY SOONER. 

MODEL DISCUSSION: NUMERICAL MODELS ARE IN TIGHT AGREEMENT WITH AN
EVEN SPREAD TO 107NM BY TAU 36, LENDING HIGH CONFIDENCE TO THE JTWC
TRACK FORECAST. THERE IS ONLY MEDIUM CONFIDENCE IN THE INTENSITY
FORECAST DUE TO THE POSSIBILITY OF AN EARLIER DISSIPATION.

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