Advisories

WDPN34 PGTW 102100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 15W (FIFTEEN) 
WARNING NR 004//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 27.5N 160.2E
   INITIAL INTENSITY: 25 KTS
   GEOGRAPHIC REFERENCE: 605 NM NORTHWEST OF WAKE ISLAND
   MOVEMENT PAST 6 HOURS: WESTWARD AT 04 KTS
   SIGNIFICANT WAVE HEIGHT: 11 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS A FULLY
EXPOSED LOW-LEVEL CIRCULATION CENTER WITH CONVECTION HEAVILY
SHEARED TO ITS EAST. THE DECOUPLING OF THE LOW AND MID-LEVEL
CIRCULATIONS OCCURRED RAPIDLY OVER THE PAST 6 HOURS AND HAS
RENDERED THE REMAINING LLCC OF TROPICAL DEPRESSION 15W
QUASI-STATIONARY OVER THE PAST SEVERAL HOURS. A 101521Z AMSR-2 WIND
SPEED PRODUCT CONFIRMED WIND SPEEDS OF 25 KTS OR LESS SURROUNDING
THE EXPOSED LLCC. THE INITIAL POSITION IS PLACED WITH HIGH
CONFIDENCE BASED ON THE FULLY EXPOSED LLCC IN THE EIR IMAGERY. THE
INITIAL INTENSITY OF 25 KTS IS ASSESSED WITH HIGH CONFIDENCE BASED
ON THE AMSR-2 WIND SPEED PRODUCT, DESPITE HIGHER AGENCY DVORAK AND
CIMSS OBJECTIVE INTENSITY ESTIMATES. THE ENVIRONMENT IS
CHARACTERIZED AS UNFAVORABLE, PRIMARILY DUE TO THE HIGH (25-30 KTS)
VERTICAL WIND SHEAR (VWS) COUPLED WITH VERY LITTLE REMAINING
OUTFLOW ALOFT.

INITIAL WIND RADII BASIS: NOT APPLICABLE 

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
   RJTD: T1.0 - 25 KTS
   KNES: T2.5 - 35 KTS
   PHFO: T2.0 - 30 KTS
   CIMSS SATCON: 36 KTS AT 101700Z
   CIMSS ADT: 35 KTS AT 101800Z
   CIMSS AIDT: 29 KTS AT 101800Z
   CIMSS D-MINT: 31 KTS AT 101547Z
   CIMSS D-PRINT: 31 KTS AT 101800Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: UNFAVORABLE
   VWS: 25-30 KTS
   SST: 28-29 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 IS EXPECTED TO
CONTINUE ON A PREDOMINANTLY NORTHWARD TRAJECTORY OVER THE NEXT 12
HOURS UNDER THE INFLUENCE OF THE CYCLONIC LOW-LEVEL FLOW OF THE
BROAD GYRE CIRCULATION SITUATED TO THE WEST. AFTER TAU 12, THE
REMAINING SHALLOW VORTEX APPROACHES EASTERLY LOW-LEVEL FLOW AND IS
EXPECTED TO TAKE ON A NORTHWESTWARD TRAJECTORY. THERE IS A BRIEF
PERIOD NEAR TAU 24 WHERE TD 15W MAY BE INFLUENCED BY TROPICAL STORM
(TS) 13W (PEILOU) AS BOTH SYSTEMS DISSIPATE IN THE HIGH SHEAR
ENVIRONMENT. NOW THAT THE LLCC HAS FULLY DECOUPLED FROM THE
MID-LEVELS, THE INTENSITY IS FORECAST TO STEADILY DECREASE IN AN
ENVIRONMENT THAT WILL BE HOSTILE TO ANY SUSTAINED CONVECTION. FULL
DISSIPATION OVER WATER IS EXPECTED BY TAU 24.

MODEL DISCUSSION: MODEL TRACK GUIDANCE HAS A FAIRLY WIDE SPREAD
OVER THE NEXT 24 HOURS BUT OVERALL THEY AGREE ON A PRIMARILY
NORTHWARD COMPONENT FOLLOWED BY A SHIFT NORTHWESTWARD. THE JTWC
TRACK IS PLACED CLOSE TO THE MULTI-MODEL CONSENSUS WITH MEDIUM
CONFIDENCE THROUGHOUT THE FORECAST PERIOD. THE INTENSITY GUIDANCE
REMAINS ON THE HIGHER END, WITH THE EXCEPTION OF HAFS-A WHICH
DEPICTS A MORE REALISTIC CHARACTERIZATION OF THE SHALLOW VORTEX.
THEREFORE, THE JTWC INTENSITY FORECAST IS PLACED CLOSER TO THE
HAFS-A SOLUTION WITH MEDIUM CONFIDENCE. 

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