WDPS33 PGTW 152100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 15P (FIFTEEN) WARNING 
NR 001//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 17.0S 164.5W
   INITIAL INTENSITY: 35 KTS
   GEOGRAPHIC REFERENCE: 333 NM EAST-NORTHEAST OF NIUE
   MOVEMENT PAST 6 HOURS: EAST-SOUTHEASTWARD AT 10 KTS
   SIGNIFICANT WAVE HEIGHT: 17 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS TROPICAL
CYCLONE (TC) 15P (FIFTEEN) MODERATELY CONSOLIDATING WITH CONTINUING
FLARING CONVECTION AND ASSOCIATED OVERSHOOTING TOPS LOCATED
OVERHEAD AND JUST NORTH OF THE ASSESSED SHALLOW LOW-LEVEL BANDING
WRAPPING CYCLONICALLY INTO THE LOW-LEVEL CIRCULATION CENTER (LLCC).
SEA SURFACE TEMPERATURES (SST) REMAIN HIGH BETWEEN 27C AND 29C
WHILE VERTICAL WIND SHEAR (VWS) CONTINUES BETWEEN 5-10 KNOTS,
HOWEVER, TWO REGIONS OF OBSERVABLE ENHANCED VWS IS EVIDENT ON THE
ANIMATED WATER VAPOR IMAGERY, INDICATING MODERATE TO STRONG VWS
(25-30 KNOTS) LOCATED DIRECTLY TO THE NORTH AND SOUTH OF THE
OVERALL TC STRUCTURE. MODERATE DIVERGENCE ALOFT IS PREVALENT ALONG
THE NORTHERN AND SOUTHERN PERIPHERIES OF THE SYSTEM. THE INITIAL
POSITION IS PLACED WITH MEDIUM CONFIDENCE BASED ON A 151651Z 89GHZ
MICROWAVE IMAGE, WHILE THE EAST-SOUTHEASTWARD TRACK WAS CONFIRMED
ON AN EARLIER 151235Z AMSR2 PASS. THE INTITIAL INTENSITY OF 35
KNOTS IS ASSESSED WITH MEDIUM CONFIDENCE BASED ON DVORAK INTENSITY
ESTIMATES.

INITIAL WIND RADII BASIS: PERSISTENCE 

CURRENT STEERING MECHANISM: DEEP-LAYER SUBTROPICAL RIDGE (STR) TO
THE EAST.

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

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE
   VWS: 5-10 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: MODERATE POLEWARD AND EQUATORWARD

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

3. FORECAST REASONING.

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

FORECAST DISCUSSION: TC 15P IS FORECAST TO CONTINUE TRACKING TO THE
SOUTHEAST THROUGH THE END OF THE FORECAST PERIOD AS THE
ANTICYCLONIC ROTATION AROUND THE WELL-ESTABLISHED STR STEER THE
CYCLONE TO THE SOUTHEAST AND UNDER THE MID-LATITUDE WESTERLIES.
BEGINNING TAU 24, TC 15P IS EXPECTED TO CONTINUE SOUTHEASTWARD
TOWARD COOLER WATERS (24C-26C) AND START ITS TRANSITION TO BECOMING
EXTRATROPICAL BY TAU 48, AS ENHANCED THERMAL ADVECTION IS
FORECASTED TO STEADILY INCREASE AS THE CYCLONE TRACKS TOWARD THE
MID-LATITUDE LONGWAVE PATTERN. AS ENVIRONMENTAL CONDITIONS REMAIN
MARGINALLY FAVORABLE THROUGH TAU 24, THE TROPICAL CYCLONE IS
FORECAST TO GRADUALLY INTENSIFY TO NEAR 50 KNOTS AS UPPER-LEVEL
OUTFLOW AND WARM SEA-SURFACE TEMPERATURES (27C-29C) AID IN SLOW
DEVELOPMENT; HOWEVER, INCREASING VWS (25-30 KNOTS), COOLER AND
DRIER AIR WRAPPING INTO THE WESTERN SEMICIRCLE OF THE CYCLONE, AND
PROGRESSIVELY COOLER SST (24C-26C) TO THE SOUTH WILL ASSIST IN THE
EXTRATROPICAL TRANSITION BETWEEN TAUS 24 AND TAU 48. 

MODEL DISCUSSION: GLOBAL NUMERICAL MODEL GUIDANCE IS IN VERY GOOD
AGREEMENT THAT TC 15P WILL TRACK TO THE SOUTHEAST THROUGH TAU 48 AS
STEERING MECHANISMS FORCE THE CYCLONE TO THE SOUTHEAST AND
EVENTUALLY UNDER THE MID-LATITUDE WESTERLIES. THE JTWC TRACK
CONSENSUS AT TAU 24 DISPLAYS A CROSS-TRACK SPREAD OF JUST 50 NM,
WHILE TAU 48 INCREASES TO 100 NM, LENDING HIGH CONFIDENCE TO THE
0-48 INTERVAL. THE INTENSITY CONSENSUS MEMBERS REFLECT HIGH
CONFIDENCE TO THE FORECAST, WITH AN INTENSITY SPREAD OF LESS THAN
10 KNOTS THROUGHOUT THE FORECAST PERIOD, MAINTAINING A MAX
INTENSITY OF BETWEEN 45-50 KNOTS, AND STEADILY DECREASING TO
BETWEEN 40-45 KNOTS BY TAU 48 AS NEGATIVE ENVIRONMENTAL FACTORS
COMPLETE THE CYCLONE'S EXTRATROPICAL TRANSITION.

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