Tropical Storm MUIFA Advisory 9月9日

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 14W (MUIFA) WARNING NR
010//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
SUMMARY:
   INITIAL POSITION: 17.4N 130.0E
   INITIAL INTENSITY: 45 KTS
   GEOGRAPHIC REFERENCE: 560 NM SOUTH-SOUTHEAST OF KADENA AB
   MOVEMENT PAST 6 HOURS: WESTWARD AT 08 KTS
   SIGNIFICANT WAVE HEIGHT: 19 FEET
SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS A MORE
SYMMETRIC SYSTEM WITH PERSISTENT DEEP CONVECTION BEGINNING TO WRAP
INTO THE UPSHEAR SIDE, WHICH IS FULLY OBSCURING THE LOW LEVEL
CIRCULATION CENTER (LLCC). ANIMATED WATER VAPOR IMAGERY SHOWS AN
ELONGATED TROPICAL UPPER TROPOSPHERIC TROUGH (TUTT) NOW POSITIONED
TO THE NORTHWEST OF THE LLCC, IMPARTING INCREASED POLEWARD OUTFLOW,
ALLOWING FOR BETTER CONSOLIDATION AND THUS A MORE SYMMETRICAL
CONVECTIVE STRUCTURE. AN EARLIER 080915Z SYNTHETIC APERTURE RADAR
(SAR) IMAGE ALSO INDICATES A MORE SYMMETRIC DEFINED WIND FIELD
WRAPPING AROUND THE SYSTEM, AND EXTRAPOLATION OF THIS FEATURE
PROVIDES HIGH CONFIDENCE TO THE INITIAL POSITION. THE INITIAL
INTENSITY OF 45 KNOTS IS ASSESSED WITH MEDIUM CONFIDENCE BASED ON
A BLEND OF AGENCY DVORAK CURRENT INTENSITY ESTIMATES ALONG WITH
CIMSS SATCON INDICATING AN INTENSITY OF 42 KNOTS. OVERALL, THE
CURRENT ENVIRONMENT IS FAVORABLE ALONG WITH THE CORE BECOMING
VERTICALLY STACKED AND MORE SYMMETRICAL.
INITIAL WIND RADII BASIS: PERSISTENCE
CURRENT STEERING MECHANISM: MID-LEVEL SUBTROPICAL RIDGE (STR) TO
THE EAST
AGENCY DVORAK AND AUTOMATED FIXES:
   PGTW: T3.5 - 55 KTS
   RJTD: T3.0 - 45 KTS
   KNES: T3.5 - 55 KTS
   CIMSS SATCON: 39 KTS AT 081659Z
   CIMSS ADT: 36 KTS AT 081000Z
FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 0-5 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: MODERATE POLEWARD AND EQUATORWARD
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: TS 14W HAS TRACKED GENERALLY WESTWARD OVER THE
PAST 12 HOURS ALONG THE WESTERN PERIPHERY OF AN ELONGATED MID-LEVEL
SUBTROPICAL RIDGE TO THE EAST. ENVIRONMENTAL FACTORS ARE FAVORABLE
CHARACTERIZED BY LOW VERTICAL WIND SHEAR (0-5 KNOTS), WARM SEA
SURFACE TEMPERATURES (29-20C), ALONG WITH INCREASING DUAL CHANNEL
OUTFLOW BOTH POLEWARD AND EQUATORWARD, EVIDENT IN WATER VAPOR
IMAGERY. OVER THE NEXT 12 HOURS, THE GENERAL MOTION OF 14W IS
FORECAST TO TURN SHARPLY TO NORTHWESTWARD AS THE SUBTROPICAL RIDGE
(STR) BUILDS SOUTH OF HONSHU AND REORIENTS IN A MORE SOUTHEAST TO
NORTHWEST AXIS, AT THE SAME TIME THE SYSTEM WILL CONTINUE TO BECOME
BETTER ORGANIZED WHILE INTENSIFYING TO TYPHOON STRENGTH BEYOND TAU
36. BY TAU 72, THE INTENSITY IS FORECAST TO PEAK, AT THE SAME TIME
THE TRACK MOTION BEGINS TO SLOW AS THE STEERING PATTERN WEAKENS. BOTH
GFS AND ECMWF DETERMINISTIC MODELS INDICATE THE STR WILL STRENGTHEN
OVER HONSHU AND BECOME THE DOMINATE STEERING FEATURE PREVENTING THE
INTERACTION OF A SHORT WAVE TROUGH TO THE NORTHWEST AND INFLUENCE THE
SYSTEM AS PREVIOUSLY FORECASTED. THIS CHANGE IN THE STEERING DYNAMICS
WOULD RESULT IN A MORE QUASI-STATIONARY TRACK THAT COULD ULTIMATELY
DRIFT CLOSER TO TAIWAN POSITIONED IN AN AREA OF LOW OCEAN HEAT CONTENT
(OHC) WHILE INDUCING EVEN MORE COLD WATER UP WELLING. AS A RESULT, THE
INTENSITY FORECAST CALLS FOR A GRADUAL WEAKENING TREND FROM TAU 96 TO
TAU 120.
MODEL DISCUSSION: NUMERICAL MODEL TRACK GUIDANCE IS IN OVERALL GOOD
AGREEMENT ON THE OVERALL SCENARIO, WITH DETERMINISTIC GUIDANCE
TRACKERS GRADUALLY SPREADING TO A MODEST 130NM BY TAU 72. AFTER
WHICH AS MENTIONED IN THE FORECAST DISCUSSION, MANY MODEL TRACKERS
AS WELL AS THE DETERMINISTIC MODELS INCLUDING GFS AND ECMWF, ARE
INDICATING A QUASI-STATIONARY PERIOD AFTER TAU 72. HOWEVER, NAVGEM,
GALWEM, AND HWRF CONTINUE TRACKING THE SYSTEM IN A MORE NORTHERLY
DIRECTION AWAY FROM THE QUASI-STATIONARY SCENARIO BY THE END OF THE
FORECAST PERIOD. FOR THESE REASONS, THE JTWC TRACK FORECAST UP TO TAU
72 IS PLACED WITH HIGH CONFIDENCE, WHILE IN THE EXTENDED FORECAST
PERIOD, THE GUIDANCE SHOWS INCREASED UNCERTAINTY, WITH ACROSS AND
ALONG-TRACK SPREAD BOTH INCREASING TO NEARLY 300NM BY TAU 120.
RELIABLE MODEL INTENSITY GUIDANCE REMAINS IN OVERALL FAIR AGREEMENT
OF STRENGTHENING UP TO TAU 72. AFTER WHICH ALL MODEL INTENSITY
GUIDANCE SHOW A DOWNWARD TREND THROUGH THE REMAINDER OF THE
FORECAST. THEREFORE, THE JTWC INTENSITY FORECAST IS PLACED WITH
MEDIUM CONFIDENCE.
FORECAST CONFIDENCE:
   TRACK 0 - 72 HR: HIGH
   TRACK 72-120 HR: LOW
   INTENSITY 0 - 72 HR: MEDIUM
   INTENSITY 72-120 HR: MEDIUM//
NNNN
NNNN