Tropical Storm TWENTYFIVE Advisory Mi, 19.10.

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 25W (TWENTYFIVE)
WARNING NR 001//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
SUMMARY:
   INITIAL POSITION: 20.8N 130.3E
   INITIAL INTENSITY: 25 KTS
   GEOGRAPHIC REFERENCE: 369 NM SOUTH-SOUTHEAST OF KADENA AB
   MOVEMENT PAST 6 HOURS: WEST-SOUTHWESTWARD AT 04 KTS
   SIGNIFICANT WAVE HEIGHT: 10 FEET
SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS A
CONSOLIDATING SYSTEM WITH FLARING DEEP CONVECTION OBSCURING THE
LOW-LEVEL CIRCULATION CENTER (LLCC). THE INITIAL POSITION IS PLACED
WITH MEDIUM CONFIDENCE BASED ON AN EARLIER PARTIAL 191256Z ASCAT-C
IMAGE, WHICH SHOWS AN ELONGATED BUT DEFINED CENTER WITH 20-25 KNOT
WINDS OVER THE NORTHWESTERN PERIPHERY. THE INITIAL INTENSITY OF 25
KTS IS ASSESSED WITH HIGH CONFIDENCE BASED ON THE PGTW, RJTD DVORAK
ESTIMATES OF T1.5 AND ASCAT DATA. ENVIRONMENTAL CONDITIONS ARE
MARGINALLY FAVORABLE WITH WEAK EQUATORWARD OUTFLOW, WARM (28-29C)
SEA SURFACE TEMPERATURES (SSTS), AND LOW (05-10KTS) VERTICAL
WIND SHEAR (VWS).
INITIAL WIND RADII BASIS: NOT APPLICABLE (THERE ARE NO INITIAL WIND
RADII).
CURRENT STEERING MECHANISM: SUBTROPICAL RIDGE (STR) TO THE
NORTHWEST
AGENCY DVORAK AND AUTOMATED FIXES:
   PGTW: T1.5 - 25 KTS
FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE
   VWS: 5-10 KTS
   SST: 28-29 CELSIUS
   OUTFLOW: WEAK EQUATORWARD
ANALYSIS CONFIDENCE:
   INITIAL POSITION: MEDIUM
   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: TD 25W IS FORECAST TO TRACK GENERALLY WESTWARD
ALONG THE SOUTHEASTERN PERIPHERY OF THE SUBTROPICAL RIDGE (STR)
POSITIONED TO THE NORTHWEST THROUGH THE NEXT 48-72 HOURS. BY TAU
72, THE SYSTEM IS FORECAST TO SLOW AS IT REACHES A COL AREA OF WEAK
STEERING FLOW, BEFORE BEGINNING TO TURN SOUTHWESTWARD. AFTER TAU
72, A DEEP LAYER RIDGE OVER EAST CHINA WILL THEN BECOME THE MAIN
STEERING FEATURE WHICH WILL ALSO INDUCE A WEAK NORTHEASTERLY SURGE
EVENT. THIS WILL RESULT IN THE SYSTEM TRACKING
WEST-SOUTHWESTWARD AND THEN SOUTHWESTWARD THROUGH THE REMAINED OF
THE FORECAST. TD 25W WILL STEADILY INTENSIFY THROUGH THE NEXT 48-72
HOURS AS THE OVERALL ENVIRONMENT IS ONLY MARGINALLY FAVORABLE DUE TO
WARM (28-29C) SEA SURFACE TEMPERATURES (SSTS), LOW (05-10KTS)
VERTICAL WIND SHEAR (VWS) OFFSET BY WEAK OUTFLOW ALOFT DUE TO THE
UPPER LEVEL WESTERLIES FORECAST TO REMAIN FURTHER NORTH WHICH WILL
PROHIBIT GOOD POLEWARD OUTFLOW. BETWEEN TAU 72 AND TAU 96, AS THE
SYSTEM MOVES SOUTHWESTWARD INTO THE SOUTH CHINA SEA WHERE SSTS ARE
WARM ALONG WITH IMPROVED OUTFLOW, THERE IS A WINDOW OF OPPORTUNITY
FOR THE SYSTEM TO EXPERIENCE A BRIEF INTENSIFICATION PERIOD UP TO
50 KNOTS. THEN BY TAU 120, THE SYSTEM WILL TRACK NEAR COOLER
UP-WELLED WATERS FROM THE COLD WAKE 23W LEFT BEHIND ALONG WITH DRY
AIR FORECAST TO INCREASE AROUND THE SYSTEM WHICH WILL RESULT IN
STEADY WEAKENING THROUGH THE END OF THE FORECAST.
MODEL DISCUSSION: WITH THE EXCEPTION OF EGRI, COTI, WHICH ARE THE
NORTHERN OUTLIERS, NUMERICAL MODEL GUIDANCE IS IN FAIR AGREEMENT
THROUGH THE FORECAST PERIOD WITH A LARGE SPREAD OF 70-170NM FROM
TAU 72 TO TAU 120. THE BULK OF THE ECMWF ENSEMBLE (EPS) AND GFS
ENSEMBLE (GEFS) SOLUTIONS SUPPORT THE JTWC FORECAST TRACK THROUGH
TAU 72, WITH INCREASING UNCERTAINLY BY TAU 120. THEREFORE, THE JTWC
FORECAST TRACK IS POSITIONED CLOSE TO THE MULTI-MODEL CONSENSUS
WITH MEDIUM CONFIDENCE. THE RELIABLE INTENSITY GUIDANCE IS IN FAIR
AGREEMENT AND SUPPORTS AN INTENSIFICATION PHASE WITH AHVI
INDICATING A PEAK INTENSITY NEAR 65 KNOTS, ABOVE THE INTENSITY
CONSENSUS PEAK OF 50 KNOTS. GEFS INDICATES HIGH PROBABILITY OF
STEADY INTENSIFICATION AND A 10-20 PERCENT CHANCE OF MODERATE
INTENSIFICATION BETWEEN TAU 48 AND TAU 96. THEREFORE, THE JTWC
FORECAST INTENSITY IS PLACED WITH MEDIUM CONFIDENCE.
FORECAST CONFIDENCE:
   TRACK 0 - 72 HR: MEDIUM
   TRACK 72-120 HR: MEDIUM
   INTENSITY 0 - 72 HR: MEDIUM
   INTENSITY 72-120 HR: LOW//
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