Advisories

WDPN31 PGTW 140900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 16W (NANGKA) 
WARNING NR 008//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 28.4N 153.7E
   INITIAL INTENSITY: 30 KTS
   GEOGRAPHIC REFERENCE: 253 NM NORTH OF MINAMI TORI SHIMA
   MOVEMENT PAST 6 HOURS: EASTWARD AT 04 KTS
   SIGNIFICANT WAVE HEIGHT: 12 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: 
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS A FULLY EXPOSED 
AND INCREASINGLY RAGGED LOW LEVEL CIRCULATION CENTER (LLCC), WITH 
ISOLATED CONVECTIVE ACTIVITY FLARING ALONG THE CONVERGENT ASYMPTOTE IN 
THE NORTHEAST QUADRANT. OUTSIDE OF THE SMALL REGION OF FLARING 
CONVECTION, WHICH CANNOT PERSIST DUE TO THE HIGH WESTERLY SHEAR, THE 
SYSTEM IS DEVOID OF CONVECTION AND DEFINED BY LOW-LEVEL CLOUD 
STRUCTURES. ANIMATED WATER VAPOR IMAGERY SHOWS THE SYSTEM BENEATH A 
TIGHT GRADIENT IN THE UPPER-LEVEL PATTERN, GENERATING STRONG WESTERLY 
FLOW AND HIGH SHEAR OVER TOP OF THE SYSTEM. THE INITIAL POSITION IS 
ASSESSED WITH HIGH CONFIDENCE BASED ON THE EXPOSED LLCC IN THE MSI. 
THE INITIAL INTENSITY IS ASSESSED WITH HIGH CONFIDENCE BASED ON A 
BLEND OF THE OBJECTIVE AND SUBJECTIVE INTENSITY ESTIMATES BELOW, 
CLARIFIED BY PERSISTENCE WITH EARLIER SCATTEROMETER DATA. 
ENVIRONMENTAL CONDITIONS ARE HIGHLY UNFAVORABLE, WITH HIGH WESTERLY 
VWS AND DRY AIR ENTRAINMENT OFFSETTING THE WARM SSTS AND STRONG 
OUTFLOW ALOFT.

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

CURRENT STEERING MECHANISM: WEAK STEERING PATTERN, AS THE STEERING
MECHANISM SHIFTS FROM THE NEAR EQUATORIAL RIDGE (NER) TO THE SOUTH
AND THE WESTERN EXTENSION OF A SUBTROPICAL RIDGE (STR) FAR TO THE
EAST. 

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.5 - 35 KTS
   RJTD: T2.5 - 35 KTS
   RCTP: T2.0 - 30 KTS
   CIMSS SATCON: 39 KTS AT 140440Z
   CIMSS ADT: 25 KTS AT 140600Z
   CIMSS AIDT: 34 KTS AT 140600Z
   CIMSS D-MINT: 30 KTS AT 140252Z
   CIMSS D-PRINT: 31 KTS AT 140610Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: UNFAVORABLE
   VWS: 30-35 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: STRONG EASTWARD
   OTHER FACTORS: SIGNIFICANT MID-LEVEL DRY AIR ENTRAINMENT. 

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) 16W IS NEARING THE END 
OF ITS LIFE CYCLE. WHILE CURRENTLY IN A WEAK STEERING ENVIRONMENT, THE 
WESTERN EXTENSION OF AN EXPANSIVE STR FAR TO THE EAST IS EXPECTED TO 
SOON TAKE OVER AS THE DOMINANT STEERING INFLUENCE. ONCE THIS OCCURS, 
TD 16W WILL ACCELERATE EASTWARD FOR THE REMAINDER OF THE FORECAST 
PERIOD. REGARDING INTENSITY, NOW THAT THE VORTEX IS COMPLETELY 
DECOUPLED AND THE REMNANT VORTEX IS CAPPED BY DRY AIR ABOVE 700MB, THE 
SYSTEM WILL RAPIDLY WEAKEN AND DISSIPATE AS A TROPICAL CYCLONE WITHIN 
THE NEXT 12 TO 24 HOURS.

MODEL DISCUSSION: TRACK GUIDANCE HAS NOW COME INTO MUCH IMPROVED
AGREEMENT, THE ONLY REMAINING MODEL SHOWING A NORTHWARD TRACK BEING
THE UKMET ENSEMBLE MEAN. THE REMAINDER OF THE GUIDANCE PACKAGE IS
TIGHTLY PACKED ALONG AN EASTWARD TRAJECTORY, SUPPORTING THE JTWC
FORECAST WITH HIGH CONFIDENCE. INTENSITY GUIDANCE IS IN GOOD
AGREEMENT, THOUGH ALL GUIDANCE MEMBERS DEPICT THE SYSTEM REMAINING
AT OR ABOVE 30 KNOT INTENSITY THROUGH TAU 120, WHICH IS HIGHLY
UNLIKELY. THE JTWC FORECAST DEVIATES FROM THE GUIDANCE IN SHOWING
DISSIPATION BY TAU 24.

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