Advisories

WDPN31 PGTW 130900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 16W (NANGKA) WARNING NR 
004//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 27.8N 149.9E
   INITIAL INTENSITY: 35 KTS
   GEOGRAPHIC REFERENCE: 496 NM EAST-NORTHEAST OF IWO TO
   MOVEMENT PAST 6 HOURS: NORTHEASTWARD AT 21 KTS
   SIGNIFICANT WAVE HEIGHT: 13 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS AN ELONGATED
LOW-LEVEL CIRCULATION CENTER (LLCC), WITH THE FAR SOUTHWESTERN 
PERIPHERY BEGINNING TO BECOME EXPOSED OUTSIDE OF THE CONVECTIVE CIRRUS 
SHIELD. OVER THE PAST SIX HOURS, THE SYSTEM HAS MOVED OVER A MUCH 
WARMER POOL OF OCEANIC WATERS NORTH OF A COLD-WATER WAKE ASSOCIATED 
WITH THE RECENT PASSAGE OF STY BAVI. SIMULTANEOUSLY, THE SYSTEM HAS 
MOVED UNDER A REGION OF HIGHLY DIVERGENT UPPER-LEVEL FLOW, WHICH HAS 
TRIGGERED A RECENT BURST IN INTENSE CONVECTION. EARLIER SCATTEROMETER 
DATA INDICATED THAT THE LLCC HAS CONSOLIDATED BENEATH THE CONVECTION, 
AT LEAST TEMPORARILY. HOWEVER, STRONG SOUTHWESTERLY SYNOPTIC FLOW IS 
GENERATING HIGH (25-30 KT) VERTICAL WIND SHEAR (VWS). DRY MID-LEVEL 
AIR IS ALSO BEGINNING TO INTRUDE FROM THE WEST. THE INITIAL POSITION 
IS ASSESSED WITH LOW CONFIDENCE BASED ON AN EXTRAPOLATION OF A 130327Z 
AMSR2 89GHZ MICROWAVE IMAGE. THE INITIAL INTENSITY IS ASSESSED WITH 
MEDIUM CONFIDENCE BASED ON A BLEND OF THE OBJECTIVE AND SUBJECTIVE 
INTENSITY ESTIMATES OUTLINED BELOW. ENVIRONMENTAL CONDITIONS ARE 
MARGINAL, WITH WARM SSTS AND STRONG POLEWARD OUTFLOW ALOFT OFFSET BY 
HIGH VWS AND DRY AIR ENTRAINMENT.

INITIAL WIND RADII BASIS: PERSISTENCE 

CURRENT STEERING MECHANISM: NORTHERN FLANK OF A LOW- TO MID-LEVEL
NEAR EQUATORIAL RIDGE (NER) AS WELL AS A BAND OF MONSOONAL
WEST-SOUTHWESTERLY FLOW ASSOCIATED WITH A REVERSE ORIENTED MONSOON
TROUGH. 

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.5 - 35 KTS
   RJTD: T2.0 - 30 KTS
   RCTP: T2.5 - 35 KTS
   KNES: T2.0 - 30 KTS
   CIMSS SATCON: 4- KTS AT 130440Z
   CIMSS ADT: 37 KTS AT 130610Z
   CIMSS AIDT: 45 KTS AT 130610Z
   CIMSS D-MINT: 30 KTS AT 130406Z
   CIMSS D-PRINT: 37 KTS AT 130610Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINAL
   VWS: 25-30 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: STRONG POLEWARD
   OTHER FACTORS: DRY AIR ENTRAINMENT ALONG THE WESTERN FLANK. 

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

3. FORECAST REASONING.

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

FORECAST DISCUSSION: THE STEERING PATTERN CONTINUES TO EVOLVE AND
REMAINS HIGHLY UNCERTAIN. THE GFS, REPRESENTING THE BULK OF THE
PHYSICS-BASED DYNAMIC MODELS, DEPICTS AN EXTENSION OF THE NER BUILDING
NORTHWARD ALONG 160E, WHILE SIMULTANEOUSLY A STR BUILDS SOUTHEASTWARD, 
ULTIMATELY MERGING INTO ONE NORTH-SOUTH ORIENTED RIDGE COMPLEX 
POSITIONED EAST OF TS 16W. THIS RESULTS IN THE BULK OF THE DYNAMIC 
MODELS TURNING THE SYSTEM NORTH, THEN NORTHWEST AFTER TAU 12. THE 
ECMWF, REPRESENTING THE BULK OF THE AI-BASED MODELS, DEPICTS ROUGHLY 
THE SAME OVERALL EVOLUTION OF THE STEERING PATTERN, ONLY DELAYED BY 
ABOUT 24 HOURS, WHICH ALLOWS TS 16W TO CONTINUE TRACKING EASTWARD FOR 
LONGER BEFORE ENTERING A WEAK AND COMPETING STEERING REGIME BY THE END 
OF THE FORECAST. THE EXPERIMENTAL JTWC SUPER-ENSEMBLE IS ALSO SHOWING 
A BIFURCATED TRACK ENVELOPE, WITH HALF OF THE MEMBERS TRACKING 
NORTHWARD, AND THE OTHER HALF MOVING EASTWARD AFTER TAU 12, THOUGH OF 
NOTE, THE ECEPS MEAN HAS NOW JOINED THE EASTWARD-MOVING GROUP. IN 
LIGHT OF THE RECENT SHIFT IN THE ECEPS AND ECMWF, TS 16W IS FORECAST 
TO CONTINUE TRACKING NORTHEASTWARD THROUGH THE ENTIRETY OF THE 
FORECAST PERIOD. TRACK SPEEDS WILL BEGIN TO DECREASE SHARPLY AFTER TAU 
12, AS THE SYSTEM MOVES INTO A WEAK AND COMPETING STEERING 
ENVIRONMENT. REGARDING INTENSITY, THE SYSTEM WILL LIKELY BEGIN A RAPID 
VORTEX DECOUPLING WITHIN THE NEXT 12 TO 18 HOURS DUE TO STRONG 
SOUTHWESTERLY SHEAR AND INFLUX OF DRY MID-LEVEL AIR. AFTER DECOUPLING, 
THE SYSTEM WILL STEADILY WEAKEN AND ULTIMATELY DISSIPATE BY TAU 48. 

MODEL DISCUSSION: TRACK GUIDANCE DEPICTS AN EXTREME AMOUNT OF 
UNCERTAINTY, WITH THE CONSENSUS PACKAGE DIVERGING TO A 600NM
CROSS-TRACK SPREAD BY TAU 48. THE NORTHWESTWARD GROUP CONSISTS OF 
NAVGEM, JGSM, UKMET ENSEMBLE, GFS, AND GEFS. ON THE OTHER END OF THE 
ENVELOPE ARE GOOGLE DEEPMIND, EC-AIFS, ECMWF, ECEPS, AND THE JTWC 
EXPERIMENTAL AI CONSENSUS MEAN ALONG WITH MULTIPLE GFS AI-VARIANTS. AS 
DISCUSSED ABOVE, ANALYSIS SUGGESTS THE EASTWARD TRACKING GROUP IS 
GAINING TRACTION, WITH SOME MAJOR MODELS SHIFTING SIDES WITH THIS RUN. 
LASTLY, A TRACK DENSITY ANALYSIS OF THE SUPER-ENSEMBLE MEMBERS 
SUGGESTS A FOCUS ON AN EASTWARD TRACK, LENDING HIGHER CONFIDENCE TO 
THE JTWC FORECAST TRACK. INTENSITY GUIDANCE IS IN GOOD AGREEMENT, BUT 
MAINTAINS THE SYSTEM AT A HIGHER INTENSITY FOR LONGER THAN THE JTWC 
FORECAST, AND DOES NOT REFLECT DISSIPATION UNTIL MUCH LATER. HOWEVER, 
BASED ON THE MARGINAL ENVIRONMENT, ANTICIPATED DRY AIR INTRUSION AND 
VORTEX DECOUPLING AND FRAGILE NATURE OF THE CORE DUE TO ITS SMALL 
SIZE, THE JTWC FORECAST DEVIATES FROM THE GUIDANCE, THOUGH CONFIDENCE 
REMAINS MEDIUM. 

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