Tropical Storm MUIFA Advisory Fr, 09.09.

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 14W (MUIFA) WARNING NR
011//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
SUMMARY:
   INITIAL POSITION: 18.1N 129.5E
   INITIAL INTENSITY: 55 KTS
   GEOGRAPHIC REFERENCE: 513 NM SOUTH OF KADENA AB
   MOVEMENT PAST 6 HOURS: NORTHWESTWARD AT 08 KTS
   SIGNIFICANT WAVE HEIGHT: 20 FEET
SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) SHOWS THAT WHILE THE
OVERALL CONVECTIVE STRUCTURE HAS IMPROVED, WITH CONVECTIVE TOWERS
CONTINUING TO FLARE UP AND ROTATE UPSHEAR, THEY THEN DIE OFF, SO
THE CORE RING OF CONVECTION HAS YET TO BE ESTABLISHED WITH ANY
PERMANENCY. AN EARLIER 082020Z SSMIS 37GHZ MICROWAVE IMAGE
REVEALED A WEAK MICROWAVE EYE FEATURE, WHILE THE 91GHZ FREQUENCY
REVEALS A RING OF CYCLONICALLY CURVED DEEP CONVECTION FOCUSED TO
THE EAST AND FRAGMENTED BANDING FEATURES TO THE SOUTH AND WEST. SO
WHILE THE SYSTEM HAS BECOME MORE SYMMETRIC OVER THE PAST 24 HOURS,
IT STILL HAS SOME WORK TO DO. THE INITIAL POSITION IS ASSESSED WITH
MEDIUM CONFIDENCE BASED ON MULTI-AGENCY FIX POSITIONS AND
EXTRAPOLATION OF THE PREVIOUSLY MENTIONED MICROWAVE EYE FEATURE.
THE INITIAL INTENSITY IS ASSESSED WITH MEDIUM CONFIDENCE BASED ON A
BLEND OF AVAILABLE AGENCY DVORAK CURRENTLY INTENSITY ESTIMATES, AS
OBJECTIVE FIX DATA IS UNAVAILABLE DUE TO DATA OUTAGES UPSTREAM. THE
CIMSS SHEAR ANALYSIS IS ALSO UNAVAILABLE DUE TO THE OUTAGE, AND
THUS ENVIRONMENTAL ASSESSMENT IS LARGELY BASED ON HAND ANALYSIS AND
MODEL DERIVED VALUES, AND IS FAIRLY LOW CONFIDENCE. ANIMATED WATER
VAPOR IMAGERY SHOWS THE TROPICAL UPPER-TROPOSPHERIC TROUGH (TUTT)
CELL THAT HAS BEEN LURKING TO THE NORTH OF THE SYSTEM HAS SLID
SLIGHTLY TO THE WEST, BUT THE FLOW AROUND THIS TUTT IS STILL
IMPARTING SOME WESTERLY SHEAR OVER TS 14W AS EVIDENCED BY THE
CONVECTIVE STRUCTURE BEING LOPSIDED TOWARDS THE EAST AND SOUTH. THE
WATER VAPOR IMAGERY ALSO SHOWS GOOD EQUATORWARD OUTFLOW AND A
DEVELOPING POLEWARD CHANNEL UP THE EAST SIDE OF THE TUTT. SSTS ARE
VERY WARM AND OHC HIGH, PROVIDING AMPLE ENERGY FOR DEVELOPMENT.
INITIAL WIND RADII BASIS: PERSISTENCE
CURRENT STEERING MECHANISM: SOUTHWEST PERIPHERY OF A DEEP-LAYER
SUBTROPICAL RIDGE (STR) TO THE EAST-NORTHEAST
AGENCY DVORAK AND AUTOMATED FIXES:
   PGTW: T3.5 - 55 KTS
   RJTD: T3.0 - 45 KTS
   KNES: T3.5 - 55 KTS
FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 5-10 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: MODERATE POLEWARD AND EQUATORWARD
   OTHER FACTORS: MID-LEVEL WESTERLY SHEAR
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: OVER THE PREVIOUS TWELVE HOURS TS 14W HAS
QUICKLY TURNED ONTO A NORTHWESTWARD HEADING, AS THE STEERING RIDGE
TO THE WEST HAS STRENGTHENED AND ASSUMED THE PRIMARY STEERING
INFLUENCE. NO SIGNIFICANT CHANGE IN THE STEERING IS ANTICIPATED AND
TS 14W WILL CONTINUE THIS GENERAL MOVEMENT, AT ABOUT 8-10 KNOTS,
THROUGH TAU 48. AFTER THIS POINT HOWEVER THE STEERING PATTERN
CHANGES SIGNIFICANTLY, BECOMING VERY SIMILAR TO THE PATTERN THAT
STEERED STY 12W LAST WEEK, WITH A NEAR-EQUATORIAL RIDGE (NER)
DEVELOPING TO THE SOUTH, THE STR REMAINING ENSCONCED TO THE EAST,
ANOTHER STR DEVELOPING OVER SOUTHERN CHINA AND A TROUGH TO THE
NORTHWEST, SETTING UP A NICE NEST FOR TS 14W TO GET COMFORTABLE IN.
TRACK SPEEDS WILL SLOW TO BARE STEERAGEWAY (2 KNOTS) BY TAU 72 AND
THE SYSTEM WILL DRIFT SLOWLY NORTH-NORTHWESTWARD, REMAINING SOUTH
OF THE RYUKUS, THROUGH THE END OF THE FORECAST PERIOD. AS DISCUSSED
ABOVE, WHILE THE STRUCTURE HAS IMPROVED, THE SYSTEM STILL HAS SOME
WORK TO DO BEFORE IT CAN REALLY INTENSIFY. SO ANOTHER 12 HOURS OF
RATHER SLOW INTENSIFICATION IS EXPECTED, THOUGH IT IS ANTICIPATED
IT WILL REACH TYPHOON STRENGTH BY TAU 12 IF NOT EARLIER. ONCE THE
POLEWARD OUTFLOW CHANNEL IS FIRMLY IN PLACE AND THE LOW LEVEL
CIRCULATION CENTER (LLCC) CONSOLIDATED, THE SYSTEM WILL POP AN EYE
AND RAPID INTENSIFICATION (RI) IS ANTICIPATED TO ENSUE AFTER TAU
12, UNDER VERY FAVORABLE ENVIRONMENTAL CONDITIONS. THE SYSTEM IS
FORECAST TO INTENSIFY TO A PEAK OF 115 KNOTS BY TAU 48. IT THEN
WILL MOVE OVER THE RELATIVELY COOL, VERY LOW OHC POOL LEFT IN THE
WAKE OF STY 12W, SLOW DOWN AND REMAIN OVER THIS COOL POOL FOR UP TO
48 HOURS, LEADING TO RAPID WEAKENING TO A MINIMUM TYPHOON STRENGTH
SYSTEM BY THE END OF THE FORECAST.
MODEL DISCUSSION: DETERMINISTIC MODEL TRACKERS ARE IN FAIRLY GOOD
AGREEMENT IN THE EARLY PORTION OF THE FORECAST, WITH A SPREAD OF
LESS THAN 75NM AT TAU 48. BUT THEN THE TRACKERS BEGINS TO DIVERGE
RAPIDLY, WITH THE GFS, ECMWF AND ECMWF ENSEMBLE MEAN SHOWING THE
SYSTEM BECOMING QUASI-STATIONARY AND REMAINING SOUTH OF THE RYUKUS
THROUGH TAU 120. THE REMAINDER OF THE GUIDANCE INCLUDING THE NAVGEM,
GALWEM, HWRF, UKMET AND UKMET ENSEMBLE DOES NOT CAPTURE THE
QUASI-STATIONARY PERIOD AND PUSHES ON THROUGH THE NORTH, WITH THE
GALWEM AND UKMET POSITIONING THE CENTER JUST EAST OF SHANGHAI BY
TAU 120. AT TAU 120 CROSS-TRACK SPREAD IS 320NM, WHILE ALONG-TRACK
SPREAD INCREASES TO 415NM BETWEEN THE OUTLIERS. THE MAIN FACTOR
INFLUENCING THE MODEL SPREAD IS THE STRENGTH AND SOUTHWARD EXTENT
OF THE DEEP UPPER-LEVEL TROUGH TO THE WEST AND THE AMOUNT AND
TIMING OF THE STR EROSION TO THE EAST. THE FIRST GROUP FAVORS A
WEAKER, SLOWER TROUGH AND RIDGE EROSION SCENARIO WHILE THE SECOND
GROUP FAVORS THE OPPOSITE. THE JTWC FORECAST THROUGH TAU 72 IS
ASSESSED WITH MEDIUM CONFIDENCE AND LIES NEAR THE CONSENSUS MEAN.
THEREAFTER CONFIDENCE DECREASES TO LOW AND FAVORS THE GFS AND ECMWF
SOLUTIONS. INTENSITY GUIDANCE IS IN FAIR AGREEMENT, WITH A PEAK
ENVELOPE BETWEEN 95 KNOTS (DECAY-SHIPS) AND 125 KNOTS (COAMPS-TC RI
CONSENSUS). THE JTWC FORECAST LIES ON THE HIGHER END OF THE
GUIDANCE WITH MEDIUM CONFIDENCE TO TAU 72, BUT LOW CONFIDENCE
THEREAFTER AS THE ULTIMATE END OF FORECAST INTENSITY IS HIGHLY
DEPENDENT ON THE RATE OF WEAKENING OVER THE COOL POOL AND THE TRACK
SPEED THROUGH IT.
FORECAST CONFIDENCE:
   TRACK 0 - 72 HR: MEDIUM
   TRACK 72-120 HR: LOW
   INTENSITY 0 - 72 HR: MEDIUM
   INTENSITY 72-120 HR: LOW//
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