WDPS31 PGTW 051500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 10P (TEN) WARNING NR 
001//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 14.7S 164.9W
   INITIAL INTENSITY: 35 KTS
   GEOGRAPHIC REFERENCE: 338 NM EAST OF PAGO PAGO
   MOVEMENT PAST 6 HOURS: EASTWARD AT 13 KTS
   SIGNIFICANT WAVE HEIGHT: 16 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
TROPICAL CYCLONE (TC) 10P (TEN) HAS RAPIDLY CONSOLIDATED AND
INTENSIFIED OVER THE PAST 12 HOURS AFTER PASSING CLOSE TO THE
ISLANDS OF AMERICAN SAMOA. ANIMATED ENHANCED INFRARED (EIR)
SATELLITE IMAGERY SUGGESTS THAT THE SYSTEM MAY HAVE REACHED AN
INITIAL PEAK ABOUT 3-4 HOURS AGO, WHEN DEEP CONVECTION WITH
OVERSHOOTING TOPS APPROACHING -91C DEVELOPED NEAR THE ASSESSED LOW
LEVEL CIRCULATION CENTER (LLCC). OVER THE LAST COUPLE OF HOURS
HOWEVER, THE EIR LOOP DEPICTS A MUCH MORE DISORGANIZED CONVECTIVE
STRUCTURE, WITH WARMING CLOUD TOPS. A 051143 GMI 89GHZ MICROWAVE
IMAGE SHOWS A SHEARED SYSTEM, WITH THE DEEP CONVECTION ORGANIZED IN
A COMMA-SHAPED REGION TO THE EAST OF LOW-LEVEL BANDING FEATURES,
WHICH ARE EXPOSED TO THE WEST OF THE PRIMARY CONVECTIVE AREA. THE
INITIAL POSITION IS ASSESSED WITH MEDIUM CONFIDENCE BASED ON
ANALYSIS OF THE MICROWAVE IMAGERY NOTED ABOVE. THE INITIAL
INTENSITY IS ASSESSED WITH MEDIUM CONFIDENCE BASED ON THE T2.5 (35
KNOTS) DVORAK CURRENT INTENSITY ESTIMATES FROM KNES AND PHFO.
ADDITIONALLY, A 050916Z METOP-C ASCAT ULTRA-HIGH RESOLUTION (UHR)
PASS REVEALED 35-37 KNOT WINDS IN THE NORTHERN HEMISPHERE OF THE
SYSTEM, WHICH PROVIDES HIGH CONFIDENCE TO THE WIND RADII
ASSESSMENT. THE SYSTEM IS TRACKING EASTWARD THROUGH A MARGINALLY
FAVORABLE ENVIRONMENT CHARACTERIZED BY LOW (10-15 KTS) VWS, WARM
SSTS, AND STRONG POLEWARD OUTFLOW ENHANCED BY MODERATE EQUATORWARD
OUTFLOW.

INITIAL WIND RADII BASIS: SCATTEROMETER DATA 

CURRENT STEERING MECHANISM: SOUTHWESTERN PERIPHERY OF A DEEP-LAYER
SUBTROPICAL RIDGE (STR) CENTERED TO THE NORTHEAST. 

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T1.5 - 25 KTS
   KNES: T2.5 - 35 KTS
   PHFO: T2.5 - 35 KTS

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE
   VWS: 10-15 KTS
   SST: 30-31 CELSIUS
   OUTFLOW: STRONG POLEWARD
   OTHER FACTORS: MODERATE EQUATORWARD OUTFLOW. 

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

3. FORECAST REASONING.

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

FORECAST DISCUSSION: TC 10P IS FORECAST TO BEGIN TURNING ONTO A
SOUTHEASTWARD TRACK BY TAU 12 AND BEGIN TO ACCELERATE AS THE
GRADIENT ON THE SOUTHWEST SIDE OF THE STR STRENGTHENS. THE SYSTEM
WILL CONTINUE TRACKING SOUTHEASTWARD THROUGH TAU 36, BEFORE THE
TRACK FLATTENS OUT AS THE STEERING LEVEL LOWERS AND THE RIDGE
WEAKENS. THE FORECAST TRACK TAKES THE SYSTEM JUST NORTHEAST OF THE
COOK ISLANDS THROUGH TAU 36, THEN APPROACHES TAHITI FROM THE SOUTH
BY THE END OF THE FORECAST. IN THE NEAR-TERM, THE VERY STRONG
POLEWARD OUTFLOW, ENHANCED BY A MODERATE EQUATORWARD OUTFLOW
CHANNEL, IS EXPECTED TO OFFSET INCREASING WEST-NORTHWESTERLY SHEAR
AND ALLOW THE SYSTEM TO INTENSIFY UP TO A MAXIMUM OF 40-45 KNOTS IN
THE NEXT 12 HOURS. CONDITIONS RAPIDLY CHANGE AFTER TAU 18, WITH
SHEAR FORECAST TO INCREASE SHARPLY TO ABOVE 30 KNOTS WITH EVEN
HIGHER MID-LEVEL SHEAR VALUES, WHICH WILL QUICKLY DECAPITATE THE
SYSTEM, LEADING TO RAPID WEAKENING AND DISSIPATION. THE SYSTEM IS
FORECAST TO DISSIPATE BY TAU 72, BUT LIKELY WILL DISSIPATE BELOW
WARNING CRITERIA AT OR BEFORE TAU 60. IT IS POSSIBLE THAT AFTER THE
SYSTEM DISSIPATES AS A TROPICAL CYCLONE, IT MAY RESTRENGTHEN AS IT
TRANSITIONS TO A SUBTROPICAL SYSTEM BEYOND TAU 96.  

MODEL DISCUSSION: DETERMINISTIC AND ENSEMBLE TRACK GUIDANCE IS IN
GOOD AGREEMENT THAT THE SYSTEM WILL TRACK SOUTHEASTWARD THROUGH TAU
36, THEN FLATTEN OUT TO A MORE EASTWARD TRACK THEREAFTER.
CROSS-TRACK SPREAD REACHES 155NM AT TAU 72 AND THE JTWC FORECAST
LIES CLOSE TO THE MULTI-MODEL CONSENSUS MEAN WITH MEDIUM
CONFIDENCE. INTENSITY GUIDANCE FOR THE MOST PART IS IN GOOD
AGREEMENT, WITH THE EXCEPTION OF THE SHIPS GUIDANCE (BOTH NAVGEM
AND GFS) WHICH APPEARS TO BE UNREALISTICALLY HIGH, PEAKING THE
SYSTEM AT NEAR 60 KNOTS AT TAU 48. THE REMAINDER OF THE GUIDANCE
PACKAGE SHOWS A PEAK BETWEEN 45-50 KNOTS BETWEEN TAU 24 AND TAU 36,
FOLLOWED BY A SHARP WEAKENING TREND THEREAFTER. THE JTWC FORECAST
TRACKS BELOW THE CONSENSUS MEAN WHICH IS BEING PULLED TOO HIGH BY
THE SHIPS GUIDANCE, AND BREAKS FROM THE GUIDANCE IN DISSIPATING THE
SYSTEM BY TAU 72, RESULTING IN LOW CONFIDENCE. ALL OF THE GUIDANCE
SHOWS A REINTENSIFICATION BEGINNING AROUND TAU 72, BUT ANALYSIS
SUGGESTS THIS IS DUE TO BAROCLINIC FORCING AS THE SYSTEM UNDERGOES
SUBTROPICAL TRANSITION. 

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