Tropical Storm NEPARTAK Advisory Thu Jul 29

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 11W (NEPARTAK)
WARNING NR 020//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
SUMMARY:
   INITIAL POSITION: 40.2N 140.3E
   INITIAL INTENSITY: 30 KTS
   GEOGRAPHIC REFERENCE: 43 NM WEST-SOUTHWEST OF MISAWA, JAPAN
   MOVEMENT PAST 6 HOURS: NORTHWESTWARD AT 15 KTS
   SIGNIFICANT WAVE HEIGHT: 00 FEET
SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
11 (NEPARTAK) REMAINS CLASSIFIED AS A SUBTROPICAL DEPRESSION.
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS A RAGGED AND
DISORGANIZED LOW LEVEL CIRCULATION (LLC) CENTERED OVER THE FAR
WESTERN PORTION OF NORTHERN HONSHU. SCATTERED WEAK CONVECTIVE
ACTIVITY IS FLARING OVER AND JUST NORTHWEST OF THE ASSESSED CENTER,
BUT OVERALL THE CONVECTIVE STRUCTURE HAS COLLAPSED AS THE SYSTEM
CROSSED OVER THE NORTHERN JAPANESE ALPS. THE SYSTEM REMAINS UNDER
AN UPPER-LEVEL LOW, AND CIRA THERMAL CROSS SECTIONS CONTINUE TO
EXHIBIT STRONG SUBTROPICAL CHARACTERISTICS, WITH A WEAK COLD
ANOMALY IN THE LOW TO MID-LEVELS TOPPED BY A MODERATELY STRONG WARM
ANOMALY IN THE UPPER LEVELS. THE INITIAL POSITION IS ASSESSED WITH
MEDIUM CONFIDENCE, AS THERE IS A LARGE DISCREPANCY BETWEEN THE PGTW
AND RJTD FIX POSITIONS, WITH RJTD WELL OUT TO SEA WHILE PGTW
REMAINS OVER LAND. SURFACE OBSERVATIONS FROM FUKAURA AND ANIMATED
RADAR DATA ASSISTED IN REFINING THE INITIAL POSITION. THE INITIAL
INTENSITY REMAINS AT 30 KTS WITH MEDIUM CONFIDENCE BASED PRIMARILY
ON THE SURFACE PRESSURE READINGS OF 999 MB FROM FUKAURA.
INITIAL WIND RADII BASIS: NOT APPLICABLE (THERE ARE NO INITIAL WIND
RADII).
CURRENT STEERING MECHANISM: EXTENSION OF THE SUBTROPICAL RIDGE
(STR) BUILDING OVER HOKKAIDO.
AGENCY DVORAK AND AUTOMATED FIXES:
   PGTW: NO CURRENT ESTIMATE
   RJTD: T1.5 - 25 KTS
   RCTP: T1.5 - 25 KTS
   CIMSS ADT: 40 KTS AT 280540Z
FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: UNFAVORABLE
   VWS: 0-5 KTS
   SST: OVER LAND
   OUTFLOW: WEAK RADIAL
ANALYSIS CONFIDENCE:
   INITIAL POSITION: MEDIUM
   INITIAL INTENSITY: MEDIUM
   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: 11W IS MOVING FAIRLY RAPIDLY ACROSS NORTHERN
HONSHU, AND SHOULD REEMERGE OVER THE SEA OF JAPAN WITHIN THE NEXT
FEW HOURS. AS THE EXTENSION OF THE STR BUILDS IN TO THE NORTH, THE
SYSTEM WILL TRACK MORE WESTWARD AS IT MOVES INTO THE CENTRAL SEA OF
JAPAN. AS THE TRACK HAS MOVED FURTHER NORTH THAN PREVIOUSLY
FORECAST, IT WILL EMERGE OVER COOLER WATERS WITH SSTS BETWEEN 24 TO
25 CELSIUS, PRECLUDING ANY ADDITIONAL DEVELOPMENT. SIMULTANEOUSLY
THE UPPER-LEVEL LOW WHICH HAS BEEN TRACKING OVER TOP OF 11W WILL
STOP AND THEN MOVE EASTWARD OVER THE NEXT 24 HOURS, ALLOWING FOR AN
UPPER-LEVEL JET STREAK TO MOVE OVER TOP OF 11W, DRASTICALLY
INCREASING VWS AND LEADING TO DISSIPATION OVER WATER NO LATER THAN
TAU 36.
MODEL DISCUSSION: NUMERICAL MODEL GUIDANCE IS IN GOOD AGREEMENT
THROUGH THE DURATION OF THE FORECAST AND THE JTWC FORECAST TRACKS
CLOSE TO THE CONSENSUS MEAN TRACK. THE JTWC INTENSITY FORECAST
TRACKS BELOW THE INTENSITY CONSENSUS MEAN AS IT IS BEING
UNREALISTICALLY PULLED HIGHER DUE TO SOME MEMBERS NOT DECAYING THE
SYSTEM ENOUGH OVER LAND. SOME MEMBERS OF THE CONSENSUS STILL DEPICT
A WEAK VORTEX TRACKING WEST-SOUTHWEST THROUGH TAU 48 OR EVEN TAU
60, HOWEVER IN LIGHT OF THE EXPECTED IMPACT OF VERY HIGH VWS (40-50
KTS) AFTER TAU 36, WHAT LLCC THAT MAY STILL EXIST WILL NOT BE ABLE
TO REGENERATE TO MORE THAN 20 KTS.
FORECAST CONFIDENCE:
   TRACK 0 - 72 HR: HIGH
   INTENSITY 0 - 72 HR: MEDIUM//
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