WDPS31 PGTW 150300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 08P (EIGHT) WARNING NR 
003//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 14.1S 169.8E
   INITIAL INTENSITY: 35 KTS
   GEOGRAPHIC REFERENCE: 233 NM NORTH-NORTHEAST OF PORT VILA,
VANUATU
   MOVEMENT PAST 6 HOURS: SOUTHEASTWARD AT 07 KTS
   SIGNIFICANT WAVE HEIGHT: 14 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS TROPICAL
CYCLONE 08P WITH VIGOROUS BURSTS OF DEEP CONVECTION OFFSET TO THE
EAST OF THE LOW-LEVEL CIRCULATION CENTER (LLCC). WATER VAPOR
IMAGERY CONTINUES TO SHOW PROMINENT CIRRUS FILAMENTS EXPANDING
OUTWARD IN THE POLEWARD DIRECTION, INDICATIVE OF A ROBUST OUTFLOW
CHANNEL. FURTHER ENVIRONMENTAL ANALYSIS INDICATES THAT 08P IS IN A
FAVORABLE ENVIRONMENT DUE TO LOW (10-15 KTS) WESTERLY VERTICAL WIND
SHEAR AND WARM (28-29 C) SEA SURFACE TEMPERATURES. A 142138Z
METOP-C ASCAT PASS REVEALED THAT THE SURFACE CIRCULATION IS NOT
WELL-DEFINED AND THE WIND FIELD IS STILL HIGHLY ASYMMETRIC. THE
STRONGEST WINDS ARE ENTIRELY CONFINED TO THE EASTERN SEMICIRCLE
WITH MUCH WEAKER WINDS WITHIN THE WESTERN SEMICIRCLE. THE INITIAL
POSITION IS PLACED WITH MEDIUM CONFIDENCE BASED ON THE ANIMATED MSI
AND EXTRAPOLATION FROM THE AFOREMENTIONED ASCAT IMAGE. THE INITIAL
INTENSITY OF 35 KTS IS ASSESSED WITH MEDIUM CONFIDENCE BASED ON THE
SAME ASCAT IMAGE. OF NOTE, THE AGENCY DVORAK AND OBJECTIVE
INTENSITY ESTIMATES SUGGEST A HIGHER INTENSITY THAN THE ASCAT
SHOWS.

INITIAL WIND RADII BASIS: 142138Z METOP-C ASCAT SCATTEROMETER DATA 

CURRENT STEERING MECHANISM: SOUTHWESTERN PERIPHERY OF A DEEP-LAYER
NEAR EQUATORIAL RIDGE (NER) CENTERED NEAR SAMOA

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T3.0 - 45 KTS
   KNES: T3.0 - 45 KTS
   PHFO: T3.0 - 45 KTS
   CIMSS ADT: 49 KTS AT 150020Z
   CIMSS AIDT: 39 KTS AT 150020Z
   CIMSS D-PRINT: 36 KTS AT 150020Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 10-15 KTS
   SST: 28-29 CELSIUS
   OUTFLOW: STRONG POLEWARD
   OTHER FACTORS: SLIGHT DRY AIR ENTRAINMENT FROM THE WEST

ANALYSIS CONFIDENCE:
   INITIAL POSITION: MEDIUM
   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 08P IS FORECAST TO TRACK SOUTHEASTWARD OVER
THE NEXT 12 HOURS AS IT CONTINUES TO ROUND THE NER TO THE EAST.
AFTER TAU 12, THE RIDGE IS EXPECTED TO DRIFT NORTHWARD, CAUSING THE
TRAJECTORY TO BE MORE EASTWARD. 08P WILL THEN TRACK ALONG THE
SOUTHERN EXTENT OF THE NER THROUGH TAU 60, WITH A TRACK NORTH OF
FIJI. AROUND TAU 60, A SECOND NER IS EXPECTED TO BUILD NEAR 10S
170W WITH A MORE NORTHWEST-SOUTHEAST ORIENTATION. INTERACTION WITH
THIS SECOND NER IS EXPECTED TO CAUSE 08P TO TRACK MORE
SOUTHEASTWARD THROUGH TAU 96. REGARDING INTENSITY, 08P IS FORECAST
TO GRADUALLY INTENSIFY THROUGH TAU 36 AS SHEAR REMAINS LOW AND
POLEWARD OUTFLOW REMAINS ROBUST. AFTER TAU 36, WESTERLY SHEAR IS
EXPECTED TO INCREASE TO AROUND 25 KTS, CAUSING THE SYSTEM TO BEGIN
WEAKENING. NEAR TAU 72, SHEAR WILL INCREASE FURTHER, TO AROUND 40
KTS. INCREASING SHEAR AND DRY AIR ENTRAINMENT WILL FIGHT TO
COUNTERACT THE ROBUST POLEWARD OUTFLOW AS THE SYSTEM BEGINS TO
INTERACT WITH THE JET. 08P IS FORECAST TO SHALLOW OUT AND DISSIPATE
NEAR TAU 96, EAST OF FIJI. 

MODEL DISCUSSION: NUMERICAL MODEL TRACK GUIDANCE AGREES ON THE
TRAJECTORY OF THE TRACK OF 08P. HOWEVER, MODELS GREATLY DIFFER
REGARDING TRACK SPEEDS. ALONG-TRACK SPREAD AT TAU 48 IS AROUND 370
NM WHICH INCREASES TO OVER 750 NM AT TAU 96. GFS CONTINUES TO BE
THE FASTEST MODEL, TRACKING THE VORTEX SOUTHEAST OF AMERICAN SAMOA
AT TAU 96. ON THE OTHER HAND, THE ECMWF ENSEMBLE MEAN IS JUST
NORTHEAST OF FIJI AT THE SAME TIME. THE JTWC TRACK FORECAST IS
PLACED NEAR THE AVERAGE BETWEEN THE GFS AND ECMWF ENSEMBLE MEANS
THROUGHOUT THE FORECAST PERIOD WITH LOW CONFIDENCE. INTENSITY
GUIDANCE IS IN SLIGHTLY BETTER AGREEMENT THIS MODEL RUN WITH ONLY A
COUPLE RAPID INTENSIFICATION AIDS TRIGGERING. PEAK INTENSITIES
RANGE FROM 45 KTS (HAFS-A) TO 65 KTS (COAMPS-TC) AT TAU 36. MODELS
THEN GENERALLY AGREE ON WEAKENING FROM TAU 36 ONWARD. THE JTWC
INTENSITY FORECAST IS PLACED CLOSE TO THE MULTI-MODEL CONSENSUS
WITH OVERALL MEDIUM CONFIDENCE.

FORECAST CONFIDENCE:
   TRACK 00-72 HR: LOW
   TRACK 72-120 HR: LOW
   INTENSITY 00-72 HR: MEDIUM
   INTENSITY 72-120 HR: MEDIUM//
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