WDPN31 PGTW 242100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 02W (SEPAT) WARNING
NR 010//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
SUMMARY:
INITIAL POSITION: 31.3N 139.8E
INITIAL INTENSITY: 30 KTS
GEOGRAPHIC REFERENCE: 240 NM SOUTH OF YOKOSUKA, JAPAN
MOVEMENT PAST 6 HOURS: NORTH-NORTHWESTWARD AT 06 KTS
SIGNIFICANT WAVE HEIGHT: 13 FEET
SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY REVEALS A
WELL-DEFINED, YET SHALLOW AND WEAK LOW LEVEL CIRCULATION CENTER
(LLCC), AND NOW FULLY EXPOSED. A RECENTLY DEVELOPED BURST OF
CONVECTIVE ACTIVITY IS OBSERVED TO THE SOUTHEAST OF THE LLCC BUT IS
BEING PUSHED OFF THE LLCC DUE TO THE MODERATE NORTHERLY SHEAR. A
241634Z AMSR2 36GHZ MICROWAVE IMAGE INDICATES THAT THE LOWER-LEVEL
CLOUD BANDS REMAIN WELL-DEFINED, PARTICULARLY ON THE EASTERN SIDE
OF THE CIRCULATION. CONVERSELY, THE WESTERN SIDE APPEARS
SIGNIFICANTLY WEAKER AND SHALLOWER IN BOTH EIR AND MICROWAVE IMAGERY.
THE 91GHZ BAND SHOWS NO SIGNIFICANT CONVECTIVE ACTIVITY ASSOCIATED
WITH THE LLCC. THE INITIAL POSITION IS ASSESSED WITH HIGH CONFIDENCE,
PRIMARILY BASED ON THE EXPOSED LLCC IN THE EIR. THE INITIAL INTENSITY
IS ALSO ASSESSED WITH HIGH CONFIDENCE, SUPPORTED BY OBJECTIVE AND
SUBJECTIVE ESTIMATES, AS WELL AS AN EARLIER ASCAT PASS WHICH REVEALED
MAXIMUM SURFACE WINDS OF 29 KNOTS IN THE NORTHEASTERN QUADRANT.
ANIMATED WATER VAPOR IMAGERY SHOWS THE SYSTEM IS EMBEDDED WITHIN AN
UPPER-LEVEL COL FEATURE, INDICATING A LIMITED OR ABSENT UPPER-LEVEL
OUTFLOW MECHANISM. ADDITIONALLY, A WEDGE OF DRY AIR OVERLAYS THE
SYSTEM, AS INDICATED IN BOTH THE HIGH-RESOLUTION MODEL DATA AND THE
CHICHIJIMA 1200Z SOUNDING. THESE FACTORS, COMBINED WITH MODERATE
NORTHERLY SHEAR, SUGGEST THE SYSTEM HAS ENTERED AN UNFAVORABLE AND
GENERALLY HOSTILE ENVIRONMENT.
INITIAL WIND RADII BASIS: NOT APPLICABLE (THERE ARE NO INITIAL WIND
RADII).
CURRENT STEERING MECHANISM: WESTERN PERIPHERY OF A DEEP LAYER
SUBTROPICAL RIDGE (STR) CENTERED TO THE EAST.
AGENCY DVORAK AND AUTOMATED FIXES:
PGTW: T2.0 - 30 KTS
RJTD: T2.0 - 30 KTS
RCTP: T2.0 - 30 KTS
KNES: T2.0 - 30 KTS
CIMSS ADT: 32 KTS AT 241730Z
CIMSS AIDT: 36 KTS AT 241730Z
CIMSS D-MINT: 27 KTS AT 241636Z
CIMSS D-PRINT: 25 KTS AT 241750Z
FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: UNFAVORABLE
VWS: 20-25 KTS
SST: 24-25 CELSIUS
OUTFLOW: WEAK WESTWARD
OTHER FACTORS: DRY MID-LEVEL AIR.
ANALYSIS CONFIDENCE:
INITIAL POSITION: HIGH
INITIAL INTENSITY: HIGH
INITIAL WIND RADII: NOT APPLICABLE
3. FORECAST REASONING.
SIGNIFICANT FORECAST CHANGES: THERE ARE NO SIGNIFICANT CHANGES TO
THE FORECAST FROM THE PREVIOUS WARNING.
FORECAST DISCUSSION: TROPICAL DEPRESSION (TD) 02W (SEPAT) HAS
SLOWED SIGNIFICANTLY OVER THE PAST 12 HOURS AND EXHIBITED A SLIGHT
WOBBLE AS IT APPROACHES THE STR AXIS. OVER THE NEXT 12 TO 18 HOURS,
TD 02W WILL SLOWLY CROSS THE RIDGE AXIS, SUBSEQUENTLY TURNING AND
ACCELERATING NORTHEASTWARD. THE LATEST FORECAST INDICATES A SLIGHT
OFFSHORE SHIFT IN THE TRACK, WITH THE CENTER OF TD 02W IS NOW
EXPECTED TO REMAIN OFFSHORE THE BOSO PENINSULA. THE CLOSEST POINT OF
APPROACH IS PROJECTED TO OCCUR AROUND TAU 36. AFTER TAU 36, THE
SYSTEM WILL CONTINUE TO ACCELERATE TOWARDS THE NORTHEAST, OPENING THE
DISTANCE TO EASTERN HONSHU THROUGH THE REMAINDER OF THE FORECAST. TD
02W HAS WEAKENED TO TD STRENGTH OVER THE LAST 6 TO 12 HOURS AS IT HAS
MOVED INTO A LESS FAVORABLE ENVIRONMENT. HOWEVER, ALL AVAILABLE
GUIDANCE SUGGESTS A VERY SLOW RATE OF ADDITIONAL WEAKENING,
INDICATING A GRADUAL DISSIPATION. THE SYSTEM IS FORECAST TO REMAIN A
MINIMAL TD AS IT PASSES THE BOSO PENINSULA, SIMULTANEOUSLY BEGINNING
EXTRATROPICAL TRANSITION (ETT). SHORTLY AFTER TAU 36, THE SYSTEM
BEGINS TO INTERACT WITH THE DIVERGENT REGION AHEAD OF AN APPROACHING
NEGATIVELY TILTED MAJOR SHORTWAVE TROF MOVING IN FROM THE WEST. BY
THE END OF THE FORECAST, THE SYSTEM WILL START TO REINTENSIFY AS IT
COMPLETES ETT.
MODEL DISCUSSION: DETERMINISTIC AND ENSEMBLE TRACK GUIDANCE IS IN
TIGHT CROSS- AND ALONG-TRACK AGREEMENT FOR THE FIRST 24 HOURS OF
THE FORECAST. HOWEVER, ONCE THE SYSTEM CROSSES THE RIDGE AXIS AND
BEGINS TO ITS NORTHEASTWARD ACCELERATION, TRACK GUIDANCE BEGINS TO
DISPERSE, INTRODUCING SIGNIFICANT CROSS- AND ALONG-TRACK SPREAD
ACROSS THE MODEL PACKAGE. THE JTWC FORECAST REMAINS CONSISTENT WITH
PREVIOUS FORECASTS AND MULTI-MODEL CONSENSUS MEAN. INTENSITY
GUIDANCE IS MIXED, WITH ROUGHLY HALF OF THE GUIDANCE SUPPORTED A
STEADY 30-35 KNOT INTENSITY THROUGH THE WHOLE DURATION OF THE
FORECAST, AND HALF ARGUING FOR A SLOW WEAKENING THROUGH THE
FORECAST PERIOD. THE JTWC FORECAST
