WDPN31 PGTW 201500

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//

SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 07W (MEKKHALA) WARNING NR

008//

RMKS/

1. FOR METEOROLOGISTS.

2. 6 HOUR SUMMARY AND ANALYSIS.



SUMMARY:

   INITIAL POSITION: 14.3N 135.4E

   INITIAL INTENSITY: 50 KTS

   GEOGRAPHIC REFERENCE: 329 NM NORTH-NORTHWEST OF YAP

   MOVEMENT PAST 6 HOURS: WESTWARD AT 14 KTS

   SIGNIFICANT WAVE HEIGHT: 25 FEET



SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:

ANIMATED ENHANCED INFRARED IMAGERY (EIR) DEPICTS TROPICAL STORM

(TS) 07W (MEKKHALA) WITH A SYMMETRIC CENTRAL DENSE OVERCAST

COMPLETELY OBSCURING THE LOW-LEVEL CIRCULATION CENTER. A 200903Z

PARTIAL SAR IMAGE OF THE EASTERN HALF OF 07W REVEALS A HIGHLY

ASYMMETRIC WINDFIELD, WITH THE PEAK WINDS CONFINED TO A SMALL PATCH

IN THE NORTHEASTERN QUADRANT AND NO GALE FORCE WINDS IN THE

SOUTHEASTERN QUADRANT. ADDITIONALLY, THE SAR REVEALS THE LLCC WAS

STILL QUITE ELONGATED ALONG THE NORTHWEST-SOUTHEAST AXIS AT 0903Z.

A 1202Z METOP-B PARTIAL PASS OF THE CENTER AND EASTERN PERIPHERY OF

THE STORM CONFIRMS THE HIGHLY ASYMMETRIC WINDFIELD, BUT ALSO

REVEALS THE VORTEX HAS BECOME LESS ELONGATED AND GALE FORCE WINDS

HAVE APPEARED IN THE SOUTHEASTERN QUADRANT WITHIN THE PAST FEW

HOURS. ENVIRONMENTAL ANALYSIS REVEALS A FAVORABLE ENVIRONMENT,

CHARACTERIZED BY WARM (29-30 C) SEA SURFACE TEMPERATURES, LOW TO

MODERATE (15-20 KTS) VERTICAL WIND SHEAR (VWS), AND GOOD OUTFLOW

ALOFT SUPPORTED BY AN UPPER-LEVEL ANTICYCLONE. THE INITIAL POSITION

IS ASSESSED WITH HIGH CONFIDENCE BASED ON THE ASCAT IMAGE REVEALING

THE CENTER LOCATION. THE INITIAL INTENSITY OF 50 KTS IS ASSESSED

WITH HIGH CONFIDENCE BASED ON THE SAR AND ASCAT DATA.



INITIAL WIND RADII BASIS: ADJUSTED EASTERN WIND RADII BASED ON THE

200903Z SAR DATA AND THE 201202Z ASCAT DATA



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: T3.5 - 55 KTS

   CIMSS ADT: 45 KTS AT 201230Z

   CIMSS AIDT: 40 KTS AT 201230Z

   CIMSS D-PRINT: 39 KTS AT 201230Z



FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE

   VWS: 10-15 KTS

   SST: 29-30 CELSIUS

   OUTFLOW: STRONG POLEWARD



ANALYSIS CONFIDENCE:

   INITIAL POSITION: HIGH

   INITIAL INTENSITY: HIGH

   INITIAL WIND RADII: MEDIUM



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 MAINTAIN ITS

WEST-NORTHWESTWARD TRACK THROUGH TAU 60 AS IT REMAINS UNDER THE

INFLUENCE OF THE STR CENTERED TO THE NORTH. AROUND TAU 72, MEKKHALA

WILL BEGIN TO ROUND THE RIDGE, CAUSING IT TO SLOW ITS SPEED OF

ADVANCE. 07W IS EXPECTED TO ROUND THE RIDGE AXIS BETWEEN TAU 60-96

AND SUBSEQUENTLY ACCELERATE NORTH-NORTHEASTWARD THROUGH THE END OF

THE FORECAST PERIOD. REGARDING INTENSITY, 07W IS FORECAST TO

STEADILY INTENSIFY THROUGH TAU 24 WHILE IT CONTINUES TO ORGANIZE.

FOLLOWING TAU 24, 07W IS FORECAST TO RAPIDLY INTENSITY (RI) IN THE

FAVORABLE ENVIRONMENT UNTIL PEAKING AT 105 KTS AT TAU 60. FOLLOWING

THE PEAK INTENSITY, MEKKHALA IS FORECAST TO SWIFTLY WEAKEN AS IT

ENCOUNTERS AN INCREASINGLY UNFAVORABLE ENVIRONMENT DOMINATED BY

HIGH UPPER-LEVEL EASTERLY VWS. UPWELLING AND DRY AIR ENTRAINMENT

MAY CONTRIBUTE TO ADDITIONAL WEAKENING, THOUGH THE DRIVING FACTOR

IS ANTICIPATED TO BE VWS.



MODEL DISCUSSION: DETERMINISTIC TRACK MODEL GUIDANCE IS IN GOOD

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 FROM TAU 0-72 AND MEDIUM CONFIDENCE FROM TAU

72 THROUGH THE END OF THE FORECAST PERIOD. RELIABLE INTENSITY

GUIDANCE IS IN POOR AGREEMENT FOR THE DURATION OF THE FORECAST

PERIOD. GUIDANCE IS SPLIT BETWEEN THE RI AIDS AND COAMPS-TC (GFS

BOUNDARY CONDITIONS) AND THE MESOSCALE AND GLOBAL MODELS. THE RI

AIDS AND COAMPS DEPICT AN RI TREND BETWEEN TAU 0 TO TAU 36 AT THE

LATEST, WHILE HAFS AND HWRF DEPICT A VERY SLIGHT INTENSIFICATION

TREND FROM TAU 0-24 BEFORE RI. GFS DEPICTS VERY MINOR

INTENSIFICATION UNTIL TAU 60 FOLLOWED BY RAPID WEAKENING. AS A

RESULT OF THE WIDE SPREAD IN MODEL GUIDANCE, THE JTWC INTENSITY

FORECAST IS ASSESSED WITH OVERALL LOW CONFIDENCE.



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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