Tropical Storm NEPARTAK Advisory ma, 26-07

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 11W (NEPARTAK) WARNING
NR 011//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
SUMMARY:
   INITIAL POSITION: 33.5N 149.8E
   INITIAL INTENSITY: 35 KTS
   GEOGRAPHIC REFERENCE: 511 NM EAST OF YOKOSUKA, JAPAN
   MOVEMENT PAST 6 HOURS: NORTHWESTWARD AT 07 KTS
   SIGNIFICANT WAVE HEIGHT: 13 FEET
SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) SHOWS A SUBTROPICAL
SYSTEM WITH A BROAD, LONG SWATH OF CONVECTION CURLING INTO AN
ELONGATED, NARROW, AND PARTLY EXPOSED LOW LEVEL CIRCULATION (LLC).
THE MULTIPLE VORTICES OBSERVED PRIOR TO THIS WARNING CYCLE HAVE
COALESCED INTO THIS LLC, WHICH WAS THE CENTROID THAT WAS BEING
TRACKED BY JTWC. THE INITIAL POSITION IS PLACED WITH MEDIUM
CONFIDENCE ON THIS LLC WHICH WAS PARTIALLY CAPTURED BY A 252320Z
ASCAT PASS. THE INITIAL INTENSITY OF 35KTS IS BASED ON PATCHES OF
35-KT WIND BARBS DEPICTED IN THE ASCAT
PASS OVER 120NM NORTHEASTWARD FROM THE LLC UNDER THE SWATH OF
CONVECTION. ALTHOUGH NOT REPRESENTATIVE OF THE STORM POSITION, THE
INITIAL INTENSITY IS SUPPORTED BY THE PGTW DVORAK AND THE ADT
AUTOMATED FIXES.
INITIAL WIND RADII BASIS: SCATTEROMETER DATA.
CURRENT STEERING MECHANISM: SUBTROPICAL RIDGE (STR) TO THE
NORTHEAST.
AGENCY DVORAK AND AUTOMATED FIXES:
   PGTW: T2.5 - 35 KTS
   RJTD: T2.0 - 30 KTS
   RCTP: T2.0 - 30 KTS
   CIMSS SATCON: 42 KTS AT 252137Z
   CIMSS ADT: 37 KTS AT 252340Z
FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINAL
   VWS: 30+ KTS
   SST: 26-27 CELSIUS
   OUTFLOW: STRONG POLEWARD
ANALYSIS CONFIDENCE:
   INITIAL POSITION: MEDIUM
   INITIAL INTENSITY: LOW
   INITIAL WIND RADII: HIGH
3. FORECAST REASONING.
SIGNIFICANT FORECAST CHANGES: THERE ARE NO SIGNIFICANT CHANGES TO
THE FORECAST FROM THE PREVIOUS WARNING.
FORECAST DISCUSSION: SUBTROPICAL CYCLONE 11W WILL CONTINUE TO TRACK
NORTHWESTWARD UNDER THE STEERING STR ON A PINWHEEL PATTERN AROUND
AN UPPER LEVEL LOW TO THE SOUTHWEST, MAKING LANDFALL OVER NORTHERN
HONSHU NEAR KESENNUMA, JAPAN, NEAR TAU 48. THE MARGINAL ENVIRONMENT
- STRONG VWS OFFSET BY STRONG POLEWARD OUTFLOW AND WARM SST - WILL
FUEL A SLIGHT INTENSIFICATION TO 40KTS AT TAUS 24-36. AFTERWARD,
THE UPPER LEVEL LOW WILL COME INTO CLOSE PROXIMITY OF 11W AND
PROMOTE SUBSIDENCE ALOFT AND INDUCE THE INFLOW OF COLD DRY AIR IN
THE LOWER LEVELS. THESE PLUS THE TOPOGRAPHICAL EFFECTS AFTER
LANDFALL WILL GRADUALLY ERODE THE SYSTEM DOWN TO 25KTS BY THE TIME
IT EXITS INTO THE SEA OF JAPAN (SOJ) BEFORE TAU 96. THE COOLER SSTS
IN THE SOJ FOLLOWED BY A SECONDARY LANDFALL INTO HOKKAIDO AFTER THE
SYSTEM RECURVES NORTHEASTWARD AROUND THE STR
AXIS WILL FURTHER ERODE 11W TO DISSIPATION BY TAU 96.
MODEL DISCUSSION: NUMERICAL MODELS ARE IN OVERALL GOOD AGREEMENT
BUT GIVEN THE BROAD COMPLEXITY OF A SUBTROPICAL CYCLONE AND THE
UNCERTAINTY OF A LAND PASSAGE, THERE IS MEDIUM CONFIDENCE IN THE
JTWC TRACK AND INTENSITY FORECASTS UP TO TAU 72, THEN LOW
CONFIDENCE AFTERWARD.
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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