WDPS31 PGTW 180300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 09P (NINE) WARNING NR 
001//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 17.8S 161.5E
   INITIAL INTENSITY: 35 KTS
   GEOGRAPHIC REFERENCE: 366 NM NORTHWEST OF NOUMEA, NEW CALEDONIA
   MOVEMENT PAST 6 HOURS: EAST-SOUTHEASTWARD AT 11 KTS
   SIGNIFICANT WAVE HEIGHT: 18 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS A PARTIALLY
EXPOSED LOW LEVEL CIRCULATION CENTER (LLCC) WITH TWO PRIMARY SPIRAL
BANDS OF DEEP CONVECTION. A 172200Z ASCAT-B SCATTEROMETERY PARTIAL
PASS SHOWS THE EASTERN SEMICIRCLE OF TC 09P WHICH INDICATES A
RELATIVELY COMPACT CIRCULATION WITH A FIELD OF 35KT WINDS TO THE
NORTHEAST OF THE LLCC.  THE INITIAL POSITION IS PLACED WITH MEDIUM
CONFIDENCE BASED ON MSI AND PARTIAL ASCAT-B IMAGERY. THE INITIAL
INTENSITY OF 35 KTS IS ASSESSED WITH HIGH CONFIDENCE BASED ON
AGENCY DVORAK CURRENT INTENSITY ESTIMATES WHICH INDICATE 30-35KTS
HOWEVER BOTH PGTW AND KNES SHOW A FINAL T OF T2.0 DUE TO
CONSTRAINTS, WHILE THEIR DATA T NUMBERS ARE T2.5, SO THE TRUE
CONSENSUS IS NEAR 35KTS.

INITIAL WIND RADII BASIS: PARTIAL ASCAT-B SCATTEROMETER DATA 

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

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.0 - 30 KTS
   KNES: T2.0 - 30 KTS
   PHFO: T2.5 - 35 KTS
   NFFN: T2.0 - 30 KTS

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 10-15 KTS
   SST: 28-29 CELSIUS
   OUTFLOW: MODERATE POLEWARD AND EQUATORWARD

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

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: THIS INITIAL PROGNOSTIC REASONING
MESSAGE ESTABLISHES THE FORECAST PHILOSOPHY.

FORECAST DISCUSSION: TC 09P IS FORECAST TO CONTINUE TRACKING
EAST-SOUTHEASTWARD IN A FAVORABLE ENVIRONMENT CHARACTERIZED BY WARM
SEA SURFACE TEMPERATURES (SST), LOW VERTICAL WIND SHEAR (VWS), AND
SOLID DUAL CHANNEL OUTFLOW ALOFT. OVER THE NEXT 24 HOURS, AS THE
SYSTEM THREADS THE NEEDLE BETWEEN VANUATU TO THE NORTH AND NEW
CALEDONIA TO THE SOUTH, 09P IS FORECAST TO REACH A PEAK INTENSITY
OF 50KTS AND POSSIBLY A BIT HIGHER. BY TAU 36 AND THROUGH TAU 48,
THE SYSTEM WILL TURN SLIGHTLY POLEWARD AND STEADY UP ON A
SOUTHEASTERLY COURSE. DURING THIS TIME THE ENVIRONMENT WILL BEGIN
TO DEGRADE, CHARACTERIZED BY INCREASING DRY AIR ENTRAINMENT,
COOLING SEA SURFACE TEMPERATURES, DECREASED OUTFLOW ALOFT AND
BAROCLINIC INTERACTION. BY TAU 48, 09P WILL BEGIN SUBTROPICAL
TRANSITION (STT) AS IT IS FORCED FURTHER POLEWARD BY A BUILDING
SUBTROPICAL RIDGE (STR) TO THE EAST. AFTER TAU 48, HAVING CROSSED
THE 26C ISOTHERM, NOW POLEWARD OF THE STR AXIS AND UNDER INCREASING
DRY AIR ENTRAINMENT 09P WILL GRADUALLY LOSE ALL TROPICAL
CHARACTERISTICS AS IT CONTINUES TO WEAKEN BELOW 35KTS.  BY TAU 96,
NOW DEVOID OF ALL TROPICAL CHARACTERISTICS AND SOUTH OF THE 30TH
PARALLEL, 09P WILL COMPLETE STT AND CONTINUE POLEWARD EVENTUALLY
BECOMING EXTRA-TROPICAL BEYOND THE FORECAST PERIOD.

MODEL DISCUSSION: NUMERICAL MODEL GUIDANCE IS IN GOOD AGREEMENT
WITH A 100NM SPREAD IN SOLUTION THROUGH TAU 72. AFTER TAU 72 AS THE
SYSTEM COMPLETES STT MODEL GUIDANCE BEGINS TO SPREAD THROUGH THE
FORECAST PERIOD. FOR THESE REASONS THE INITIAL JTWC TRACK GUIDANCE
IS PLACED WITH HIGH CONFIDENCE AND THE EXTENDED TRACK GUIDANCE IS
PLACED WITH MEDIUM CONFIDENCE. RELIABLE MODEL INTENSITY GUIDANCE IS
IN FAIR AGREEMENT THAT AN INITIAL INTENSIFICATION TREND WILL
PERSIST THROUGH TAU 36, AFTER WHICH ALL MEMBERS EXCEPT DECAY-SHIPS
(NAVGEM AND GFS) WEAKEN THE SYSTEM THROUGH THE FORECAST PERIOD. FOR
THESE REASONS THE INITIAL JTWC INTENSITY FORECAST IS PLACED WITH
HIGH CONFIDENCE WHILE THE EXTENDED INTENSITY FORECAST IS PLACED
WITH MEDIUM CONFIDENCE.

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