WDPN31 PGTW 240900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 22W (TRAMI) WARNING NR 
016//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 17.4N 119.9E
   INITIAL INTENSITY: 40 KTS
   GEOGRAPHIC REFERENCE: 180 NM NORTH-NORTHWEST OF MANILA,
PHILIPPINES
   MOVEMENT PAST 6 HOURS: WEST-NORTHWESTWARD AT 13 KTS
   SIGNIFICANT WAVE HEIGHT: 20 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI), SURFACE
OBSERVATIONS AND INTERMITTENT RADAR DATA SUGGEST THAT TROPICAL
STORM (TS) 22W (TRAMI) HAS UNDERGONE A LEE-SIDE JUMP, WITH REMNANTS
OF A LOW LEVEL CIRCULATION CENTER (LLCC) HANGING BACK OVER NORTHERN
LUZON, WHILE MID-LEVEL ROTATION HAS JUMPED OUT OVER THE EASTERN
SOUTH CHINA SEA, BUILDING BACK DOWN TO THE SURFACE. A 240307Z WSF-M
37GHZ MICROWAVE IMAGE REVEALED A WEAK ROTATION CENTER JUST WEST OF
VIGAN, PHILIPPINES WITH WELL-DEFINED LOW-LEVEL SPIRAL BANDING
FEATURES WRAPPING INTO THE CENTER FROM THE NORTH AND WEST. THE
INITIAL POSITION WAS ASSESSED WITH MEDIUM CONFIDENCE BASED ON THE
MICROWAVE IMAGERY NOTED ABOVE AND THE AGENCY FIX POSITIONS. THE
INITIAL INTENSITY WAS ASSESSED WITH LOW CONFIDENCE, BUT SLIGHTLY
ABOVE THE AVERAGE OF AGENCY DVORAK FIXES NOTED BELOW, IN LIGHT OF
HIGHER CIMSS DPRINT AND DMINT ESTIMATES. THE SYSTEM HAS MOVED OVER
THE RUGGED TERRAIN OF NORTHERN LUZON AND IS NOW BACK OVER WATER, IN
A GENERALLY FAVORABLE ENVIRONMENT, WITH MODERATE EQUATORWARD AND
WESTWARD OUTFLOW ALOFT, AND WARM SSTS, THOUGH MODERATE EASTERLY
SHEAR IS HAVING A DELETERIOUS EFFECT ON THE ABILITY OF THE VORTEX
TO REALIGN.

INITIAL WIND RADII BASIS: PERSISTENCE 

CURRENT STEERING MECHANISM: SOUTHERN PERIPHERY OF A DEEP
SUBTROPICAL RIDGE EXTENDING FROM NORTHERN THAILAND TO SOUTHEAST OF
TOKYO. 

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.0 - 30 KTS
   RJTD: T3.0 - 45 KTS
   KNES: T2.0 - 30 KTS
   CIMSS DPRINT: 46 KTS AT 240600Z
   CIMSS DMINT: 43 KTS AT 240535Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE
   VWS: 15-20 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: MODERATE WESTWARD
   OTHER FACTORS: MODERATE WESTWARD OUTFLOW; RESIDUAL LAND
INFLUENCES. 

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: TS 22W IS FORECAST TO CONTINUE TRACKING
WESTWARD, ALONG THE SOUTHERN SIDE OF THE STR TO THE NORTH THROUGH
THE MAJORITY OF THE FORECAST PERIOD, AT LEAST UP TO TAU 96. TRACK
SPEEDS ARE EXPECTED TO BE SLOW FOR THE FIRST 12 HOURS OR SO OF THE
FORECAST, AS THE LOW-LEVEL VORTEX RECONSOLIDATES AFTER JUMPING BACK
OVER WATER. AFTER TAU 12, FORWARD MOTION INCREASES TO ABOUT 10 OR
11 KNOTS AND WILL CONTINUE AT THIS PACE THROUGH ABOUT TAU 48 AS THE
STEERING GRADIENT REMAINS STRONG. STEADY INTENSIFICATION IS
ANTICIPATED THROUGH TAU 36, WITH THE RATE OF INTENSIFICATION BEING
LIMITED BY THE LARGE SIZE OF THE CIRCULATION, AND PERSISTENT
MODERATE EASTERLY SHEAR. A PEAK OF 55 OR 60 KNOTS IS FORECAST BY
TAU 36, FOLLOWED BY A BRIEF LEVELING OFF PERIOD THROUGH TAU 48.
THEREAFTER, SHEAR IS EXPECTED TO INCREASE FURTHER, ACCOMPANIED BY
PENETRATION OF DRY MID-LEVEL AIR USHERED IN ON THE EASTERLY SHEAR,
LEADING TO A GENERAL WEAKENING TREND THROUGH THE REMAINDER OF THE
FORECAST PERIOD. PASSAGE OF A MID-LATITUDE TROUGH TO THE NORTH
AFTER TAU 96 WILL WEAKEN THE STEERING RIDGE, WHICH ACCOMPANIED BY A
STRONG SOUTHWESTERLY MONSOONAL SURGE TO THE SOUTH AND DEVELOPMENT
OF A DEEP UPPER-LEVEL LOW ASSOCIATED WITH WHAT IS CURRENTLY INVEST
98W, WILL GENERATE A WEAK AND COMPETING STEERING PATTERN. TS 22W
WILL IN RESPONSE SLOW DOWN, THEN AS IT WEAKENS, COME UNDER THE
STEERING INFLUENCE OF THE LOW-LEVEL SOUTHWESTERLY SURGE FLOW ALONG
THE NORTHERN SIDE OF A BUILDING NEAR-EQUATORIAL RIDGE AND TURN
SHARPLY SOUTH THEN EAST BY TAU 120. 

MODEL DISCUSSION: DETERMINISTIC TRACK GUIDANCE IS IN GOOD AGREEMENT
ON THE OVERALL TRACK SCENARIO, WITH ALL CONSENSUS MEMBERS
CONCURRING ON A WESTWARD TRACK TO TAU 72 FOLLOWED BY A TURN
SOUTHWARD THEN EASTWARD. THERE REMAINS FAIRLY SIGNIFICANT
DIFFERENCES IN THE SHARPNESS OF THE TURN TO THE EAST AND THE SPEED
AT WHICH IT OCCURS, LEADING TO A LARGE SPREAD IN THE SPECIFIC
MEMBERS. THE LATEST GFS FOR INSTANCE TAKES THE SYSTEM TO LANDFALL
NEAR HUE CITY, VIETNAM BEFORE TURNING SHARPLY BACK OUT TO SEA. THE
REMAINDER OF THE GUIDANCE HOWEVER KEEPS THE SYSTEM OFFSHORE THE
ENTIRETY OF THE FORECAST PERIOD. THE JTWC FORECAST LIES CLOSE TO
THE CONSENSUS THROUGH TAU 72, THEN FOLLOWS THE ECMWF DETERMINISTIC
TRACKER THROUGH TAU 120. CONFIDENCE IS HIGH TO TAU 72, THEN LOW DUE
TO THE ERRATIC NATURE IN THE TIMING AND STRENGTH OF THE 180 DEGREE 
TURN IN THE GUIDANCE. INTENSITY GUIDANCE IS IN GOOD AGREEMENT THAT THE
SYSTEM WILL SLOWLY INTENSIFY TO TAU 48, THEN SLOWLY WEAKEN. THE
JTWC FORECAST LIES ON THE HIGHER SIDE OF THE ENVELOPE BUT
CONFIDENCE IS HIGH. 

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