Advisories

WDPN31 PGTW 121500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 16W (NANGKA) WARNING 
NR 001//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 23.0N 144.8E
   INITIAL INTENSITY: 30 KTS
   GEOGRAPHIC REFERENCE: 220 NM EAST-SOUTHEAST OF IWO TO
   MOVEMENT PAST 6 HOURS: NORTHEASTWARD AT 18 KTS
   SIGNIFICANT WAVE HEIGHT: 12 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS TROPICAL
DEPRESSION (TD) 16W (NANGKA) WITH CONSOLIDATING LOW-LEVEL CLOUD
BANDING WRAPPING INTO THE CENTER FROM ALL QUADRANTS, INDICATING THE
LOW-LEVEL CENTER HAS BECOME SIGNIFICANTLY MORE DEFINED OVER THE
PAST SEVERAL HOURS. ADDITIONALLY, THE MID-LEVEL CONVECTION IS
BECOMING BETTER ORGANIZED AND IS BEGINNING TO ROTATE AT THE
CENTER. 16W REMAINS EMBEDDED WITHIN A TROUGH, EVIDENCED BY THE
121029Z AND 121207Z ASCAT PASSES. THE PARTIAL 121029Z ASCAT ALSO
REVEALS THAT THE EASTERN SEMICIRCLE IS TIGHTLY WOUND AND
SYMMETRICAL, WITH THE 25-30 KT WINDS BEGINNING TO WRAP INTO THE
SYSTEM FROM THE SOUTH. NANGKA SITS IN A FAVORABLE ENVIRONMENT,
CHARACTERIZED BY LOW (10-15 KTS) VERTICAL WIND SHEAR (VWS), WARM
(28-29 C) SEA SURFACE TEMPERATURES (SST), MODERATE EQUATORWARD
OUTFLOW, AND IS CURRENTLY LOCATED WITHIN A POCKET OF MOISTURE. THE
INITIAL POSITION AND INTENSITY ARE PLACED WITH HIGH CONFIDENCE
BASED ON THE 1210289Z PARTIAL ASCAT PASS.

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

CURRENT STEERING MECHANISM: SOUTHWESTERLY MONSOONAL FLOW ENHANCED
BY A SUBTROPICAL RIDGE (STR) CENTERED TO THE SOUTHEAST AND A DEEP
LAYER LOW CENTERED TO THE NORTHWEST

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T1.0 - 25 KTS
   RJTD: T2.0 - 30 KTS
   RCTP: T2.5 - 35 KTS
   KNES: T1.0 - 25 KTS
   CIMSS D-PRINT: 23 KTS AT 121200Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 15-20 KTS
   SST: 28-29 CELSIUS
   OUTFLOW: MODERATE EQUATORWARD

ANALYSIS CONFIDENCE:
   INITIAL POSITION: HIGH
   INITIAL INTENSITY: HIGH
   INITIAL WIND RADII: NOT APPLICABLE

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: THIS INITIAL PROGNOSTIC REASONING
MESSAGE ESTABLISHES THE FORECAST PHILOSOPHY.

FORECAST DISCUSSION: TD 16W IS FORECAST TO TRACK NORTHEASTWARD
WHILE IT REMAINS UNDER THE STEERING INFLUENCE OF THE MONSOONAL FLOW
ENHANCED BY THE STR TO THE SOUTHEAST AND THE DEEP LAYER LOW
NORTHWEST. FROM TAU 0 UNTIL TAU 36, THE DEEP-LAYER LOW IS EXPECTED
TO BREAK DOWN AND WEAKEN THE STEERING GRADIENT, CAUSING 16W TO SLOW
ITS FORWARD MOTION SLIGHTLY AT TAU 48. 16W IS FORECAST TO REMAIN
COMPACT, SHALLOW, AND LOOSELY ORGANIZED FOR THE DURATION OF THE
FORECAST PERIOD, MAKING IT PARTICULARLY SUSCEPTIBLE TO THE
SURROUNDING ENVIRONMENT. BEGINNING AROUND TAU 24, NANGKA IS
EXPECTED TO ENCOUNTER AN INCREASINGLY HOSTILE ENVIRONMENT,
CHARACTERIZED BY FALLING SSTS, HIGH (30-35 KTS) VWS, AND
SIGNIFICANT MID-LEVEL DRY AIR ENTRAINMENT. THE COMBINATION OF THOSE
FACTORS IS EXPECTED TO QUICKLY WEAKEN THE SYSTEM AND CAUSE
DISSIPATION NO LATER THAN TAU 48. REGARDING INTENSITY, 16W HAS
APPROXIMATELY 24 HOURS TO INTENSIFY BEFORE REACHING THE UNFAVORABLE
ENVIRONMENT. THEREFORE, THE JTWC FORECAST DEPICTS A SLIGHT
INTENSIFICATION BETWEEN TAU 12-24, THEN WEAKENING UNTIL
DISSIPATION.

MODEL DISCUSSION: DETERMINISTIC MODEL TRACK GUIDANCE IS IN POOR
AGREEMENT IN TRACK GUIDANCE. THERE IS A DISTINCT BIFURCATION IN
MEMBERS, WITH THE PHYSICS-BASED MODELS DEPICTING A NORTHEASTWARD
TRACK THROUGH TAU 24, THEN A NORTHWESTWARD CURVE AS THEY DEPICT 16W
TRACKING INTO THE STEERING WEAKNESS INDUCED BY THE WEAKENING LOW.
THE EXPERIMENTAL AI-BASED MODELS DEPICT A NORTHEASTWARD TRACK
THROUGH TAU 24 AS WELL; HOWEVER FROM TAU 24-48, THEY DEPICT 16W
CONTINUING ON A GENERALLY NORTHEASTWARD TRACK INDUCED BY THE
MONSOONAL FLOW AROUND THE DEEP LAYER STR. AS A RESULT, THE JTWC
TRACK FORECAST PORTRAYS TRACK SPEEDS SLOWER THAN ALL MODEL GUIDANCE
IN AN EFFORT TO ALLOW SUFFICIENT TIME FOR MEMBERS TO COME INTO
BETTER AGREEMENT. ALTHOUGH, THE SLOWER FORWARD MOTION AT TAU 48 IS
ALSO DEPICTED BY THE PHYSICS-BASED MODELS. AS A RESULT OF THE
SIGNIFICANT UNCERTAINTY REGARDING FORECAST TRACK, THE JTWC TRACK
FORECAST IS PLACED WITH LOW CONFIDENCE. RELIABLE INTENSITY AIDS ARE
IN MODERATE AGREEMENT THROUGH THE FORECAST PERIOD, WITH THE
INTENSITY ENVELOPE RANGING FROM 25 KTS TO 35 KTS. THE JTWC
INTENSITY FORECAST CLOSELY ALIGNS THE HAFS-A SOLUTION WITH MEDIUM
CONFIDENCE.

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