WDPN31 PGTW 132100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 16W (NANGKA) WARNING NR 
006//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 28.3N 152.4E
   INITIAL INTENSITY: 35 KTS
   GEOGRAPHIC REFERENCE: 261 NM NORTH-NORTHWEST OF MINAMI TORI SHIMA
   MOVEMENT PAST 6 HOURS: EAST-NORTHEASTWARD AT 15 KTS
   SIGNIFICANT WAVE HEIGHT: 13 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS TROPICAL
STORM (TS) 16W (NANGKA) WITH A NEARLY FULLY DECOUPLED LOW LEVEL
CIRCULATION CENTER (LLCC) THAT REMAINS OBSCURED BY THE SOUTHEASTERN
PERIPHERY OF THE CENTRAL DENSE OVERCAST (CDO). ENVIRONMENTAL
CONDITIONS ARE ASSESSED TO BE MARGINAL WITH WARM (27-28 C) SEA SURFACE 
TEMPERATURES (SSTS) AND MODERATE POLEWARD OUTFLOW ALOFT OFFSET BY HIGH 
(25-30 KTS) VERTICAL WIND SHEAR (VWS), EVIDENT IN EIR AND HASTENING 
THE DECOUPLING OF THE VORTEX. A 131553Z AMSR2 89 GHZ MICROWAVE IMAGE 
FURTHER SUPPORTS THE DECOUPLING, DEPICTING THE ELONGATED LLCC WITH AN 
AREA OF CONVECTION DISPLACED TO THE NORTHEAST. THE INITIAL POSITION IS 
ASSESSED WITH MEDIUM CONFIDENCE BASED ON EXTRAPOLATION FROM THE AMSR2 
IMAGE AND ANIMATED EIR. THE INITIAL INTENSITY IS ASSESSED WITH HIGH 
CONFIDENCE BASED ON THE AGREEMENT BETWEEN AGENCY DVORAK FIXES AND 
CIMSS OBJECTIVE ESTIMATES LISTED BELOW.

INITIAL WIND RADII BASIS: 131034Z METOP-C ASCAT DATA

CURRENT STEERING MECHANISM: NEAR-EQUATORIAL RIDGE (NER) CENTERED TO
THE SOUTH

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.5 - 35 KTS
   RJTD: T2.5 - 35 KTS
   RCTP: T2.5 - 35 KTS
   KNES: T2.5 - 35 KTS
   CIMSS SATCON: 42 KTS AT 131730Z
   CIMSS ADT: 34 KTS AT 131730Z
   CIMSS AIDT: 37 KTS AT 131730Z
   CIMSS D-MINT: 36 KTS AT 131631Z
   CIMSS D-PRINT: 33 KTS AT 131900Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINAL
   VWS: 25-30 KTS
   SST: 27-28 CELSIUS
   OUTFLOW: MODERATE POLEWARD

ANALYSIS CONFIDENCE:
   INITIAL POSITION: MEDIUM
   INITIAL INTENSITY: HIGH
   INITIAL WIND RADII: HIGH

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: THERE ARE NO SIGNIFICANT CHANGES TO
THE FORECAST FROM THE PREVIOUS WARNING.

FORECAST DISCUSSION: TS 16W IS FORECAST TO CONTINUE EAST-NORTHEASTWARD 
THROUGHOUT THE FORECAST PERIOD, CURRENTLY UNDER THE STEERING INFLUENCE 
OF A NEAR-EQUATORIAL RIDGE (NER) CENTERED TO THE SOUTH. NEAR THE END 
OF THE FORECAST PERIOD, AN EXTENSION OF A SUBTROPICAL RIDGE CENTERED 
FAR TO THE EAST IS EXPECTED TO BUILD WESTWARD, RESULTING IN A FORECAST 
DECREASE IN TRACK SPEED AT TAU 36. TRACK MODEL GUIDANCE CONTINUES TO 
DEPICT A BIFURCATION SCENARIO, LENDING SOME UNCERTAINTY TO THE 
FORECAST. THE ALTERNATE SCENARIO NOT DEPICTED IN THE JTWC OFFICIAL 
FORECAST IS A POLEWARD TURN BETWEEN TAUS 12 AND 24 AS A RESULT OF THE 
STR EXTENSION BUILDING MORE QUICKLY, ALTHOUGH MORE GUIDANCE HAS 
SHIFTED OVER TIME TO DEPICT THE EASTWARD TRACK REFLECTED IN THE JTWC 
FORECAST. IN REGARDS TO INTENSITY, TS 16W IS EXPECTED TO DECREASE IN 
INTENSITY THROUGHOUT THE REMAINDER OF THE FORECAST PERIOD DUE TO THE
INCREASED VWS CAUSING DECOUPLING OF THE VORTEX AS WELL AS INCREASED
DRY AIR ENTRAINMENT, ULTIMATELY RESULTING IN DISSIPATION OF TS 16
BY TAU 48.

MODEL DISCUSSION: TRACK MODEL GUIDANCE CONTINUES TO DEPICT A
BIFURCATION SCENARIO, ALTHOUGH THE ECMWF ENSEMBLE MEAN HAS SHIFTED
NOTABLY SOUTHWARD FROM THE REMAINDER OF PHYSICS-BASED MODELS, NOW
IN GOOD AGREEMENT WITH ALL AI-BASED MODELS ON AN EASTWARD TRACK.
THE EXPERIMENTAL JTWC SUPER-ENSEMBLE DEPICTS MOST POLEWARD TRACKS
AS A HIGHER INTENSITY SYSTEM WHEREAS THE EASTWARD MEMBERS SHOW
QUICKER DISSIPATION WHICH LENDS CONFIDENCE TO THE OFFICIAL JTWC
FORECAST TRACK AS TS 16W IS CURRENTLY DECOUPLING AND EXPECTED TO
WEAKEN IN STRENGTH, REMAINING WITHIN THE SHALLOWER STEERING 
ENVIRONMENT. THE OFFICIAL JTWC TRACK FORECAST IS PLACED WITH MEDIUM 
CONFIDENCE FOR THE REMAINDER OF THE FORECAST PERIOD CLOSELY IN LINE 
WITH THE TRACK OF THE AI CONSENSUS AND SLIGHTLY SLOWER TRACK SPEED OF 
THE EC ENSEMBLE MEAN. MODEL INTENSITY GUIDANCE IS IN FAIR AGREEMENT 
FOR THE REMAINDER OF THE FORECAST PERIOD WITH SEVERAL MODELS 
MAINTAINING TS 16W OUT TO 120 HOURS. THE OFFICIAL JTWC INTENSITY 
FORECAST IS ASSESSED WITH MEDIUM CONFIDENCE, BELOW THE MULTI-MODEL 
CONSENSUS BUT CLOSELY IN LINE WITH THE EXPERIMENTAL GOOGLE DEEPMIND 
WHICH ALSO DEPICTS DISSIPATION BY TAU 48.

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