WDPN31 PGTW 200300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 07W (MEKKHALA) WARNING NR 
006//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 14.2N 137.8E
   INITIAL INTENSITY: 45 KTS
   GEOGRAPHIC REFERENCE: 283 NM NORTH OF YAP
   MOVEMENT PAST 6 HOURS: WEST-NORTHWESTWARD AT 08 KTS
   SIGNIFICANT WAVE HEIGHT: 21 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS TROPICAL
STORM 07W MEKKHALA BEGINNING TO DEVELOP MORE TIGHTLY WRAPPED SPIRAL
BANDING, BUT WITH A LOW LEVEL CIRCULATION CENTER (LLCC) THAT HAS
BECOME MORE EXPOSED, NOW OFFSET SOUTHEAST OF THE CENTRAL DENSE
OVERCAST (CDO) INSTEAD OF SOUTHWEST AS IT WAS 12 HOURS AGO. THIS
PRECESSION OF THE VORTEX TILT IS LIKELY FACILITATED BY THE VERTICAL
WIND SHEAR (VWS) BACKING TO MORE SOUTHERLY VICE THE SOUTHWESTERLY
VWS OBSERVED SIX HOURS AGO. THE TRACK SPEED OF TS 07W HAS SLOWED
OVER THE PAST SIX HOURS AS PRECESSION OF THE VORTEX CAUSES A
SHORT-TERM WOBBLE, TEMPORARILY DETRACTING FROM THE FORWARD MOTION
OF THE LLCC. ENVIRONMENTAL ANALYSIS REVEALS FAVORABLE CONDITIONS
WITH WARM (29-30 C) SEA SURFACE TEMPERATURES (SSTS), LOW TO
MODERATE (10-15 KTS) VWS, AND MODERATE RADIAL OUTFLOW ALOFT. THE
INITIAL POSITION IS ASSESSED WITH HIGH CONFIDENCE BASED ON THE
PARTIALLY EXPOSED LLCC VISIBLE IN SATELLITE IMAGERY. THE INITIAL
INTENSITY IS ASSESSED WITH MEDIUM CONFIDENCE BASED ON THE AGENCY
DVORAK FIXES AND AUTOMATED OBJECTIVE INTENSITY AIDS LISTED BELOW.

INITIAL WIND RADII BASIS: PERSISTENCE 

CURRENT STEERING MECHANISM: SUBTROPICAL RIDGE (STR) CENTERED TO THE
NORTH.

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T3.0 - 45 KTS
   RJTD: T2.5 - 35 KTS
   KNES: T3.0 - 45 KTS
   CIMSS ADT: 53 KTS AT 192330Z
   CIMSS AIDT: 46 KTS AT 192330Z
   CIMSS D-MINT: 36 KTS AT 192040Z
   CIMSS D-PRINT: 38 KTS AT 192300Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 10-15 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: MODERATE POLEWARD

ANALYSIS CONFIDENCE:
   INITIAL POSITION: HIGH
   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: TROPICAL STORM 07W IS FORECAST TO TRACK
WEST-NORTHWESTWARD ALONG THE SOUTHERN PERIPHERY OF A SUBTROPICAL
RIDGE (STR) CENTERED TO THE NORTH OF THE SYSTEM. THEN BETWEEN TAUS
60 AND 72, TS 07W IS FORECAST TO BEGIN RECURVING TO THE NORTH AS IT
NEARS A WEAKNESS IN THE STR, ASSUMING A NORTHWARD HEADING AFTER TAU
96. SOME SLOWING OF THE STORM MOTION IS ALSO EXPECTED DURING THIS
TURN DUE TO WEAKENING STEERING CURRENTS AND THE LACK OF A DEEP
LONGWAVE TROUGH NEARBY TO PICK UP THE SYSTEM. IN TERMS OF
INTENSITY, TS MEKKHALA IS FORECAST TO CONTINUE INTENSIFYING AS
ORGANIZATION IMPROVES, THOUGH LIKELY NOT RAPIDLY DURING THE FIRST
24 HOURS DUE TO THE STILL TILTED AND ASYMMETRIC NATURE OF THE
VORTEX. DURING THE 24 TO 60 HOUR PERIOD, RAPID INTENSIFICATION IS
FORECAST TO OCCUR AS THE VORTEX BECOMES VERTICALLY STACKED WITHIN A
FAVORABLE ENVIRONMENT. PEAK INTENSITY IS FORECAST TO OCCUR BETWEEN
TAUS 60 AND 72, FOLLOWED BY STEADY WEAKENING AFTER TAU 72 AS SHEAR
SHARPLY INCREASES ON THE SOUTHERN FLANK OF A STRONG UPPER-LEVEL
RIDGE NORTH OF THE STORM, CENTERED OVER CHINA. ADDITIONALLY,
OCEANIC UPWELLING MAY CONTRIBUTE TO THE WEAKENING TREND AFTER TAU
72 DUE TO THE SLOWING STORM MOTION. DYNAMICAL MODELS CONTINUE TO
SHOW A LARGE RANGE OF POSSIBLE INTENSITY EVOLUTIONS AFTER THE ONSET
OF VERTICAL SHEAR BEYOND TAU 72, CONTRIBUTING TO LOWER THAN AVERAGE
CONFIDENCE IN THE INTENSITY FORECAST DURING THIS LATTER PERIOD.

MODEL DISCUSSION: TRACK MODEL GUIDANCE IS IN GOOD AGREEMENT
INITIALLY BUT SPREADS DRAMATICALLY AFTER TAU 72, WITH AI-BASED
MODELS AND THE GFS MAKING UP THE WESTERN SIDE OF THE GUIDANCE
ENVELOPE, AND THE UKMET AND ECMWF MODELS MAKING UP THE EASTERN
SIDE. THE LARGEST AREA OF DISAGREEMENT LIES WITH WHEN TS 07W WILL
BEGIN ITS RECURVATURE. THE OFFICIAL JTWC FORECAST IS LAID WITH HIGH
CONFIDENCE OUT TO TAU 72, IN LINE WITH THE OFFICIAL JTWC CONSENSUS.
THE FORECAST FROM TAU 72 TO 120 IS LAID WITH MEDIUM CONFIDENCE,
SPLITTING THE DIFFERENCE BETWEEN THE GROUPINGS OF PHYSICS-BASED AND
AI-BASED MODELS. THE INTENSITY MODEL GUIDANCE IS STRONGLY SPLIT
AFTER TAU 60, WITH STATISTICAL MODELS DEPICTING MUCH LOWER
INTENSITIES THAN THE HIGH-RESOLUTION DYNAMICAL MODELS LIKE HAFS AND
COAMPS-TC. THE OFFICIAL JTWC INTENSITY FORECAST IS ASSESSED WITH
MEDIUM CONFIDENCE THROUGH TAU 72 AND LOW CONFIDENCE THEREAFTER,
PLACED ABOVE THE CONSENSUS AND MORE IN LINE WITH THE DYNAMICAL
MODELS OUT TO TAU 72. THEREAFTER, THE INTENSITY IS FORECAST TO
WEAKEN JUST ABOVE THE MULTI-MODEL CONSENSUS.

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