WDPN31 PGTW 200900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 07W (MEKKHALA) WARNING NR 
007//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 14.1N 136.8E
   INITIAL INTENSITY: 45 KTS
   GEOGRAPHIC REFERENCE: 286 NM NORTH-NORTHWEST OF YAP
   MOVEMENT PAST 6 HOURS: WESTWARD AT 10 KTS
   SIGNIFICANT WAVE HEIGHT: 21 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS TROPICAL
STORM (TS) 07W (MEKKHALA) PARTIALLY EXPOSED TO THE SOUTHEAST OF THE
CENTRAL DEEP CONVECTION. AFTER A BRIEF PERIOD WHEN THE CENTER WAS
COMPLETELY EXPOSED TO THE SOUTHEAST OF THE CENTRAL DENSE OVERCAST
(CDO), THE LOW-LEVEL CIRCULATION CENTER (LLCC) HAS RECENTLY BEGUN
TO TUCK UNDER THE CONVECTION, SIGNALING THE VORTEX IS BECOMING MORE
VERTICALLY STACKED. A 200420Z AMSR2 MICROWAVE IMAGE CONFIRMS THE
DEEP CONVECTION REMAINS CONFINED TO THE NORTHWESTERN QUADRANT AND
SUPPORTS THE INITIAL POSITION WITH HIGH CONFIDENCE. ENVIRONMENTAL
ANALYSIS REVEALS FAVORABLE CONDITIONS FOR FURTHER INTENSIFICATION,
CHARACTERIZED BY WARM (29-30 C) SEA SURFACE TEMPERATURES (SST), LOW
TO MODERATE (15-20 KTS) VERTICAL WIND SHEAR (VWS), AND STRONG
POLEWARD OUTFLOW SUPPORTED BY AN UPPER-LEVEL ANTI-CYCLONE, WITH A
SMALL WEDGE OF RELATIVELY DRIER AIR PRESENT ALONG THE SOUTHERN
SEMICIRCLE. THE LIMITING FACTOR FOR DEVELOPMENT REMAINS THE TILTED
VORTEX. THE INITIAL INTENSITY OF 45 KTS IS ASSESSED WITH MEDIUM
CONFIDENCE BASED ON THE AGENCY DVORAK FIXES AND CIMSS AUTOMATED
INTENSITY ESTIMATED 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
   RCTP: T3.0 - 45 KTS
   KNES: T3.0 - 45 KTS
   CIMSS SATCON: 53 KTS AT 200700Z
   CIMSS ADT: 51 KTS AT 200700Z
   CIMSS AIDT: 44 KTS AT 200700Z
   CIMSS D-MINT: 39 KTS AT 200420Z
   CIMSS D-PRINT: 37 KTS AT 200700Z

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

ANALYSIS CONFIDENCE:
   INITIAL POSITION: HIGH
   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 07W IS FORECAST TO CONTINUE ITS GENERAL
WEST-NORTHWESTWARD TRAJECTORY AS IT TRACKS AROUND THE STEERING STR
CENTERED TO THE NORTH. MEKKHALA HAS ASSUMED A DUE WESTWARD TRACK
OVER THE PAST 6 HOURS, HOWEVER, BEGINNING IMMINENTLY, THE STR IS
EXPECTED TO SHIFT EASTWARD AND ALLOW 07W TO TRACK NORTHWESTWARD
THROUGH TAU 60. THE SHORT-TERM TRACK MAY REMAIN WESTWARD IF THE STR
SHIFTS SLOWER THAN ANTICIPATED. TS 07W IS FORECAST TO SLOW ITS
TRANSLATIONAL SPEED AND TRACK INTO A WEAKNESS IN THE STR AROUND TAU
72. MEKKHALA IS ANTICIPATED TO ROUND THE RIDGE AXIS AROUND TAU 96
AND TRACK NORTH-NORTHEASTWARD FROM TAU 96-120. REGARDING INTENSITY,
07W IS EXPECTED TO STEADILY INTENSIFY FOR THE NEXT 24 HOURS AS THE
STORM CONTINUES TO ORGANIZE. ONCE THE VORTEX BECOMES VERTICALLY
ALIGNED AROUND TAU 24, INTENSIFICATION IS FORECAST TO BECOME MORE
VIGOROUS, WITH THE FAVORABLE ENVIRONMENT SUPPORTING LIKELY RAPID
INTENSIFICATION (RI) BETWEEN TAU 36-60. 07W IS FORECAST TO REACH
ITS PEAK INTENSITY AT TAU 72, JUST PRIOR TO ROUNDING THE RIDGE.
MEKKHALA IS EXPECTED TO WEAKEN QUICKLY THEREAFTER AS IT ENTERS INTO
A HIGH SHEAR ENVIRONMENT INDUCED BY STRONG UPPER-LEVEL EASTERLIES
NEAR 20N. UPWELLING AND DRY AIR ENTRAINMENT MAY CONTRIBUTE TO
ADDITIONAL WEAKENING, THOUGH THE DRIVING FACTOR WILL BE VWS.

MODEL DISCUSSION: DETERMINISTIC TRACK GUIDANCE IS IN STRONG
AGREEMENT THROUGH TAU 60, WITH MINIMAL SPREAD IN THE ALONG-TRACK OR
CROSS-TRACK DIRECTIONS. GUIDANCE DIVERGES AROUND TAU 72 AS 07W
BEGINS TO ROUND THE RIDGE, CAUSING AN INCREASING CROSS-TRACK SPREAD
FROM TAU 72 ONWARD. AS A RESULT, THE JTWC TRACK FORECAST IS PLACED
WITH HIGH CONFIDENCE AND MEDIUM CONFIDENCE FROM TAU 72 THROUGH THE
END OF THE FORECAST PERIOD. RELIABLE INTENSITY AIDS ARE IN POOR
AGREEMENT FOR THE DURATION OF THE FORECAST PERIOD. SEVERAL JTWC RI
AIDS HAVE TRIGGERED, INDICATING IMMINENT RI, HOWEVER RI IS NOT
FORECAST TO OCCUR UNTIL AFTER TAU 24 DUE TO THE CURRENT
DISORGANIZATION OF THE STORM. MESOSCALE AND GLOBAL MODELS ARE SPLIT
IN THE PEAK INTENSITY OF 07W: GFS INDICATES A PEAK OF 65-70 KTS AT
TAU 48 AND COAMPS-TC (NAVGEM BOUNDARY CONDITIONS) INDICATES A PEAK
OF OVER 125 KTS AT TAU 72, WITH OTHER MODELS FALLING SOMEWHERE IN
THE MIDDLE. THE JTWC INTENSITY FORECAST IS ASSESSED WITH OVERALL
LOW CONFIDENCE AS A RESULT OF THE SIGNIFICANT UNCERTAINTY REGARDING
INTENSIFICATION RATE AND PEAK.

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