Advisories

WDPN34 PGTW 101500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 15W (FIFTEEN) 
WARNING NR 003//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 27.5N 160.6E
   INITIAL INTENSITY: 30 KTS
   GEOGRAPHIC REFERENCE: 592 NM NORTH-NORTHWEST OF WAKE ISLAND
   MOVEMENT PAST 6 HOURS: NORTH-NORTHEASTWARD AT 11 KTS
   SIGNIFICANT WAVE HEIGHT: 12 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED SHORTWAVE INFRARED (EIR) SATELLITE IMAGERY DEPICTS A 
DECOUPLED VORTEX, WITH THE LOW LEVEL CIRCULATION CENTER (LLCC)
DISPLACED WEST OF SHEARED CONVECTION. A 100931Z ASCAT-B BULLSEYE
REVEALED THAT THE DECOUPLING EVENT WAS ALREADY WELL UNDERWAY BY THAT 
TIME, RESULTING IN A SHIFT SOUTHWARD OF THE 0600Z INITIAL POSITION. 
THE SCATTEROMETER DATA SHOW A WELL-DEFINED LLCC, HOWEVER THE 
ASSOCIATED WINDSPEED IS SIGNIFICANTLY LOWER THAN THE MAJORITY OF THE 
SUBJECTIVE AND OBJECTIVE INTENSITY ESTIMATES, WITH 25-30 KNOT WINDS 
LIMITED TO AN ARC ACROSS THE NORTHERN PERIPHERY OF THE CIRCULATION. 
THE INITIAL POSITION AND INTENSITY ARE ASSESSED WITH HIGH CONFIDENCE 
BASED ON AN EXTRAPOLATION OF THE ASCAT DATA. ENVIRONMENTAL CONDITIONS 
HAVE DETERIORATED FASTER THAN EXPECTED, WITH WESTERLY SHEAR 
INCREASING SHARPLY OVER THE PAST SIX HOURS, LEADING TO THE 
DECOUPLING EVENT.

INITIAL WIND RADII BASIS: NOT APPLICABLE (THERE ARE NO INITIAL WIND
RADII).

CURRENT STEERING MECHANISM: EASTERN PERIPHERY OF A LARGE, LOW-LEVEL
CYCLONIC GYRE CENTERED TO THE WEST. 

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.0 - 30 KTS
   KNES: T2.5 - 35 KTS
   PHFO: T2.5 - 35 KTS
   CIMSS SATCON: 42 KTS AT 100940Z
   CIMSS ADT: 35 KTS AT 101200Z
   CIMSS AIDT: 44 KTS AT 101200Z
   CIMSS D-MINT: 33 KTS AT 101128Z
   CIMSS D-PRINT: 41 KTS AT 101240Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: UNFAVORABLE
   VWS: 20-25 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: WEAK EASTWARD

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) 15W, WITH A NOW FULLY
DECOUPLED VORTEX, WILL TRACK NORTHWARD ALONG THE EASTERN PERIPHERY OF 
THE LOW-LEVEL CYCLONIC GYRE CENTERED TO THE EAST THROUGH THE FORECAST 
PERIOD. UPPER-LEVEL WESTERLY FLOW IS EXPECTED TO CONTINUE INCREASING 
OVER THE NEXT 12 TO 24 HOURS, WHICH WILL SERVE TO BOTH INCREASE THE 
WESTERLY SHEAR AND USHER IN DRY MID-LEVEL AIR, HASTENING THE 
DISSIPATION OF TD 15W. THE REMNANT VORTEX WILL CONTINUE TO SPIN DOWN 
AND DISSIPATE WITHIN THE NEXT 24 HOURS UNDER THESE HIGHLY UNFAVORABLE 
CONDITIONS. 

MODEL DISCUSSION: TRACK GUIDANCE IS BIFURCATED WITH NAVGEM, UKMET, 
THE ECEPS MEAN, AS WELL AS THE CONSENSUS MEAN, TURNING THE SYSTEM
NORTHWESTWARD THROUGH TAU 24. MEANWHILE, THE AI MODELS, GFS, GEFS, 
AND EC-AIFS MAINTAIN A NORTHEASTWARD TRAJECTORY THROUGH THE FORECAST 
PERIOD. THE JTWC FORECAST IS BASED ON PERSISTENCE WITH THE CURRENT 
TRACK MOTION RATHER THAN ANY INDIVIDUAL MODEL. INTENSITY GUIDANCE 
ACTUALLY SHOWS SLIGHT INTENSIFICATION BEFORE GRADUALLY WEAKENING THE 
SYSTEM OVER THE COURSE OF 60 HOURS. THE JTWC FORECAST IS PLACED NEAR 
THE SOLE MODEL (HAFS-A) DEPICTING A TREND THAT REACHES DISSIPATION 
WITHIN 24 HOURS. 

FORECAST CONFIDENCE:
   TRACK 00-72 HR: MEDIUM
   INTENSITY 00-72 HR: MEDIUM//
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