Tropical Storm MALAKAS Advisory 4月7日

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 02W (TWO) WARNING
NR 001//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
SUMMARY:
   INITIAL POSITION: 3.6N 148.4E
   INITIAL INTENSITY: 25 KTS
   GEOGRAPHIC REFERENCE: 640 NM SOUTH-SOUTHEAST OF ANDERSEN AFB
   MOVEMENT PAST 6 HOURS: WEST-NORTHWESTWARD AT 08 KTS
   SIGNIFICANT WAVE HEIGHT: 10 FEET
SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS A VERY
COMPACT CIRCULATION WHICH HAS TUCKED UNDER A FLARE-UP IN CONVECTIVE
ACTIVITY, AFTER HAVING BEEN FULLY EXPOSED OVER THE PREVIOUS FEW
HOURS. THE VERY SMALL LLCC IS EMBEDDED WITHIN A LARGER REGION OF
CYCLONIC ROTATION, OUTLINED BY AREAS OF FLARING CONVECTION,
WHICH MARK THE LOW LEVEL LINES OF CONVERGENCE, PARTICULARLY ON THE
NORTHERN PERIPHERY. EVEN WITH A THE DEARTH OF RECENT MICROWAVE
IMAGERY, THANKS TO THE PREVIOUSLY EXPOSED LLCC, TRACKING VIA
ANIMATED MSI PROVIDED HIGH CONFIDENCE TO THE INITIAL POSITION. THE
INITIAL INTENSITY IS SET AT 25 KNOTS WITH HIGH CONFIDENCE BASED ON
THE CONGRUENCE ACROSS THREE FIXING AGENCIES, AS WELL AS A 062352Z
PARTIAL ASCAT-B PASS, WHICH SHOWED A SWATH OF 25KT WINDS EXTENDING
NORTH FROM THE EDGE OF THE CONVECTIVE CORE, TO THE OUTER CONVERGENT
LINE. ENVIRONMENTAL CONDITIONS ARE CONDUCIVE, THOUGH NOT HIGH
FAVORABLE AT THIS TIME, WITH WARM SSTS, AND LOW SHEAR, BUT ONLY
MODERATE EASTERLY DIFFLUENT FLOW ALOFT AND NO OUTFLOW CHANNELS.
INITIAL WIND RADII BASIS: NOT APPLICABLE (THERE ARE NO INITIAL WIND
RADII).
CURRENT STEERING MECHANISM: SOUTHERN PERIPHERY OF A DEEP-LAYER
SUBTROPICAL RIDGE (STR) TO THE NORTH.
AGENCY DVORAK AND AUTOMATED FIXES:
   PGTW: T1.5 - 25 KTS
   RJTD: T1.5 - 25 KTS
   KNES: T1.5 - 25 KTS
FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 5-10 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: MODERATE WESTWARD
ANALYSIS CONFIDENCE:
   INITIAL POSITION: HIGH
   INITIAL INTENSITY: HIGH
   INITIAL WIND RADII: NOT APPLICABLE
3. FORECAST REASONING.
SIGNIFICANT FORECAST CHANGES: THIS INITIAL PROGNOSTIC REASONING
MESSAGE ESTABLISHES THE FORECAST PHILOSOPHY.
FORECAST DISCUSSION: AFTER HAVING BEEN OBSCURED MOST OF THE NIGHT,
THE SUNRISE EXPOSED THE FACT THAT THE LLCC RESIDED TO THE EAST OF
THE PREVIOUSLY FLARING CONVECTION AND BROUGHT RENEWED CLARITY TO
THE INITIAL POSITION, WHICH WAS ADJUSTED SIGNIFICANTLY TO THE EAST
AT THE 1800Z HOUR. THE LOW LEVEL CORE HAS SINCE TUCKED UNDER A
SMALL AREA OF FLARING CONVECTION, ENABLED BY THE REDUCTION IN THE
EASTERLY SHEAR WHICH EARLIER HAD DECOUPLED THE CONVECTION FROM THE
LOW LEVEL. NOW THAT THE TWO HAVE MARRIED UP ONCE MORE, THE SYSTEM
CAN NOW BEGIN TO INTENSIFY. TD 02W IS CURRENTLY TRACKING GENERALLY
WESTWARD ALONG THE SOUTH SIDE OF A STRONG STR CENTERED NEAR 22N
160E. OVER THE NEXT 24-36 HOURS THE STR IS EXPECTED TO FIRST MOVE
TO THE EAST, THEN REORIENT TO A MORE MERIDIONAL STATE, THEN EXTEND
TO THE SOUTHWEST, RIDGING TOWARDS THE EQUATOR, UNDER TD 02W. IN
RESPONSE, TD 02W WILL GRADUALLY TURN TO MORE NORTHWEST TO
NORTH-NORTHWEST TRACK THROUGH THE NEXT 48 HOURS. AT THE END OF THE
FORECAST THE SYSTEM WILL BEGIN TO RECURVE TOWARDS THE NORTH AS IT
ROUNDS THE AXIS OF THE RIDGE. IN TERMS OF INTENSITY, DUE TO THE
SMALL NATURE OF THE CORE AND THE RELATIVELY LARGE RADIUS OF THE
OUTER MOST ISOBAR, THE SYSTEM WILL SLOWLY INTENSIFY THROUGH THE
FIRST 24-48 HOURS AS IT SLOWLY CONSOLIDATES AND UPPER-LEVEL
EASTERLY FLOW, WHILE SUPPORTIVE, IS NOT OPTIMUM FOR MORE RAPID
DEVELOPMENT. THE SYSTEM TAPS INTO A MORE FAVORABLE UPPER-LEVEL
ENVIRONMENT AFTER TAU 48, AND THE SYSTEM WILL INTENSIFY MORE
QUICKLY THEREAFTER, TO A PEAK OF 90 KNOTS BY TAU 120. THERE IS
HOWEVER AND SIGNIFICANT DELTA BETWEEN THE ECMWF AND GFS MODEL
FIELDS, WITH THE GFS DEPICTING DEVELOPMENT OF A VERY LARGE AND
INTENSE TYPHOON IN THE PHILIPPINE SEA TO THE WEST OF TD 02W. IF
THIS SYSTEM INDEED DEVELOPS, THE GFS SOLUTION, WHICH THE JTWC
FORECAST HEDGES TOWARDS, WILL BECOME MORE PROBABLE. THE ALTERNATE
SCENARIO, AS SHOWN BY THE ECMWF, IS THAT NOTHING DEVELOPS IN THE
AREA TO THE WEST AND THUS TD 02W TAKES A TRACK MUCH FURTHER TO THE
WEST, BEFORE RECURVING NEAR THE 133W LONGITUDE.
MODEL DISCUSSION: DETERMINISTIC AND ENSEMBLE TRACK GUIDANCE SHOWS A
WEAK BIFURCATION, BETWEEN THE ECMWF, THE EC ENSEMBLE, AND THE UKMET
AND ENSEMBLE ON THE WESTERN PERIPHERY, AND THE GFS, GFS ENSEMBLE
AND NAVGEM ON THE RIGHT. CROSS-TRACK SPREAD AT TAU 72 IS ROUGHLY
250NM, INCREASING TO 425NM AT TAU 120. ENSEMBLE MEMBERS ALSO SHOW A
HIGH DEGREE OF UNCERTAINTY WITH LARGE SPREAD. AT THIS POINT THE GFS
SOLUTION IS CONSIDERED MORE PROBABLE AND THUS THE JTWC FORECAST
HEDGES TOWARDS THIS MODEL SOLUTION BUT REMAINS WELL WEST OF THE GFS
DETERMINISTIC TRACK LINE DUE TO AN UNREALISTIC JUMP IN THE TRACKER
THAT GFS IS DEPICTING AT TAU 36, TRACKING THE CENTER DUE NORTH OR
EVEN NORTHEAST FOR ABOUT 24 HOURS BEFORE RESUMING THE NORTHWEST
TRACK. THIS IS UNLIKELY, AND THUS THE GFS TRACKER IS LIKELY TOO FAR
TO THE EAST WITH THIS RUN. THE JTWC FORECAST LIKES EAST OF THE
CONSENSUS MEAN AFTER TAU 72 WITH LOW CONFIDENCE. INTENSITY GUIDANCE
IS MIXED, WITH THE HWRF AND AHNI BEING OF LITTLE FAITH IN THE
SYSTEM WITH WEAK INTENSIFICATION. THE REMAINDER OF THE CONSENSUS
MEMBERS SHOW FAIRLY QUICK INTENSIFICATION TO AROUND TAU 120, WITH A
RANGE OF PEAKS BETWEEN 55-95 KNOTS. THE JTWC FORECAST LIES ON THE
LOWER END OF THE ENVELOPE AND BELOW THE MEAN THROUGH TAU 36, THEN
CROSSES TO BE HIGHER THAN THE MEAN THEREAFTER, MOST CLOSELY
TRACKING THE COAMPS-TC (GFS) GUIDANCE. CONFIDENCE IS MEDIUM THROUGH
TAU 72, AND LOW THEREAFTER.
FORECAST CONFIDENCE:
   TRACK 0 - 72 HR: MEDIUM
   TRACK 72-120 HR: LOW
   INTENSITY 0 - 72 HR: HIGH
   INTENSITY 72-120 HR: MEDIUM//
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