Tropical Storm NEPARTAK Advisory zo, 25-07

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 11W (NEPARTAK) WARNING
NR 007//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
SUMMARY:
   INITIAL POSITION: 28.8N 149.9E
   INITIAL INTENSITY: 35 KTS
   GEOGRAPHIC REFERENCE: 648 NM SOUTHEAST OF YOKOSUKA, JAPAN
   MOVEMENT PAST 6 HOURS: NORTH-NORTHWESTWARD AT 08 KTS
   SIGNIFICANT WAVE HEIGHT: 13 FEET
SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) SHOWS THE LOW LEVEL
CIRCULATION (LLC) IS NOW FULLY EXPOSED. IT IS WEAK AND RAGGED WITH
THE MAIN CONVECTION SHEARED OVER 100NM NORTHEASTWARD. THE INITIAL
POSITION IS PLACED WITH HIGH CONFIDENCE BASED ON THE LLC IN THE MSI
LOOP. THE INITIAL INTENSITY OF 35 KTS IS ASSESSED WITH LOW
CONFIDENCE BASED ON THE PGTW DVORAK THAT IS BASED ON SUBTROPICAL
METHOD.
INITIAL WIND RADII BASIS: SCATTEROMETER DATA CLOSE TO THE LLC.
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 ADT: 33 KTS AT 242340Z
FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINAL
   VWS: 30+ KTS
   SST: 27-28 CELSIUS
   OUTFLOW: STRONG POLEWARD
ANALYSIS CONFIDENCE:
   INITIAL POSITION: HIGH
   INITIAL INTENSITY: LOW
   INITIAL WIND RADII: LOW
3. FORECAST REASONING.
SIGNIFICANT FORECAST CHANGES: THERE ARE NO SIGNIFICANT CHANGES TO
THE FORECAST FROM THE PREVIOUS WARNING.
FORECAST DISCUSSION: SUBTROPICAL SYSTEM 11W WILL CONTINUE ON ITS
CURRENT TRACK MORE NORHTWESTWARD UNDER THE STR. THE MARGINAL
ENVIRONMENT WILL SUSTAIN THE CURRENT INTENSITY FOR UP TO 24HRS AS
STRONG OUTFLOW AND WARM SSTS OFFSET THE STRONG VWS. AFTERWARD, THE
CYCLONE WILL WEAKEN TO TROPICAL DEPRESSION INTENSITY AND STRUGGLE
TO MAINTAIN ITS CORE AS THE LARGE LLC BECOMES MORE IRREGULAR AND
UNWIELDY UNDER VERY STRONG VWS. ADDITIONALLY, AN UPPER LEVEL LOW
WILL STACK OVER THE SYSTEM AFTER TAU 48 AND CAUSE SUBSIDENCE ALOFT
AND STREAM COLD DRY AIR IN THE LOWER LEVELS. SHOULD 11W MAINTAIN
ITS CORE, IT WILL MAKE LANDFALL OVER HONSHU NEAR TAU 60 IN THE
VICINITY OF IWAKI AND CROSS INTO THE SEA OF JAPAN (SOJ) SHORTLY
AFTER TAU 72. THE UNUSUALLY WARM SOJ MAY REVIVE IT 30KTS. THERE IS
NOW A DISTINCT POSSIBILITY THAT THE SYSTEM WILL DISSIPATE IN THE
NEAR TERM UNDER THE INTENSE VWS AND THE ANTICIPATED NEGATIVE
EFFECTS OF THE UPPER LEVEL LOW.
MODEL DISCUSSION: NUMERICAL MODELS DIVERGE SIGNIFICANTLY ACROSS-
AND ALONG-TRACK SPREADING OUT TO OVER 380NM BY TAU 48 AND OVER
690NM BY TAU 120. ECMF  OFFERS A TRUNCATED SOLUTION, TERMINATING
THE FORECAST TRACK AT 36HRS. THESE VARYING SOLUTIONS MAY INDICATE
THE MODELS ARE HAVING DIFFICULTY TRACKING MULTIPLE WEAK VORTICES.
FORECAST CONFIDENCE:
   TRACK 0 - 72 HR: LOW
   TRACK 72-120 HR: LOW
   INTENSITY 0 - 72 HR: LOW
   INTENSITY 72-120 HR: LOW//
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