Advisories

WDPN31 PGTW 270900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 30W (IN-FA) WARNING NR 016//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 14.5N 162.1E
   INITIAL INTENSITY: 105 KTS
   GEOGRAPHIC REFERENCE: 387 NM SOUTHWEST OF WAKE ISLAND
   MOVEMENT PAST 6 HOURS: NORTHWESTWARD AT 04 KTS
   SIGNIFICANT WAVE HEIGHT: 30 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS A
COMPACT VORTEX WITH A RAGGED, CLOUD-FILLED EYE, VIGOROUS BANDS
OF DEEP CONVECTION ANCHORED ACROSS THE SOUTHEASTERN SEMICIRCLE, AND
SHALLOW CONVECTIVE BANDING ALONG THE NORTHWESTERN FLANK. A PARTIAL
270300Z WSF-M COLOR-ENHANCED 89 GHZ IMAGE REVEALED A WEAKENED INNER
EYEWALL AND A MUCH LARGER, MORE ROBUST SECONDARY OUTER EYEWALL,
INDICATIVE OF THE ONSET OF AN EYEWALL REPLACEMENT CYCLE (ERC).
THE CIMSS MICROWAVE-BASED PROBABILITY OF ERC (M-PERC) MODEL, 
UTILIZING A 270540Z SSMIS 89 GHZ IMAGE, DEPICTS A STRONG SECONDARY 
EYEWALL FORMATION EVENT, THOUGH IT FAILED TO RESOLVE THE WEAKER INNER 
EYEWALL NOTED IN THE WSF-M PASS. CALCULATED ERC PROBABILITIES HAVE 
INCREASED BUT REMAIN MODERATE AT 22 PERCENT PER M-PERC. IN THE UPPER 
LEVELS, UPPER-LEVEL DIVERGENCE IS PARTIALLY IMPEDED DUE TO THE 
PRESENCE OF THE EQUATORWARD BASE OF A 200 MB TROUGH THAT LIES JUST 
NORTH OF TY 30W. OTHERWISE, A MESOSCALE ANTICYCLONE POSITIONED OVER 
THE CORE PROVIDES FAVORABLE RADIAL OUTFLOW. THE INITIAL POSITION IS 
ASSESSED WITH HIGH CONFIDENCE BASED ON THE SSMIS MICROWAVE EYE FIX 
AND CONCURRENT EIR IMAGERY. THE INITIAL INTENSITY IS ASSESSED WITH 
MEDIUM CONFIDENCE BASED ON A BLEND OF OBJECTIVE AND SUBJECTIVE 
INTENSITY ESTIMATES OUTLINED BELOW. ENVIRONMENTAL CONDITIONS ARE 
GENERALLY FAVORABLE, CHARACTERIZED BY LOW DEEP-LAYER VERTICAL WIND 
SHEAR (VWS), WARM SEA SURFACE TEMPERATURES (SSTS), HIGH OCEANIC HEAT 
CONTENT (OHC), AND MODERATE RADIAL OUTFLOW ALOFT. HOWEVER, THE ONSET 
OF AN ERC AND LOCALIZED SEA-SURFACE COOLING INDUCED BY PROLONGED 
TRANSLATIONAL SLOWDOWN PARTIALLY OFFSET OTHERWISE FAVORABLE 
CONDITIONS.

INITIAL WIND RADII BASIS: PERSISTENCE AND OBJECTIVE BEST TRACK.

CURRENT STEERING MECHANISM: COMPETING STEERING PATTERN, WITH A
STRENGTHENING SUBTROPICAL RIDGE (STR) TO THE NORTHWEST, AND A
WEAKENING NEAR EQUATORIAL RIDGE (NER) TO THE SOUTHEAST. 

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T6.0 - 115 KTS
   RJTD: T5.5 - 102 KTS
   RCTP: T6.0 - 115 KTS
   PHFO: T6.0 - 115 KTS
   CIMSS SATCON: 112 KTS AT 270530Z
   CIMSS ADT: 107 KTS AT 270530Z
   CIMSS AIDT: 101 KTS AT 270530Z
   CIMSS D-MINT: 101 KTS AT 270300Z
   CIMSS D-PRINT: 102 KTS AT 270630Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 5-10 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: MODERATE RADIAL
   OTHER FACTORS: OCEANIC UPWELLING. 

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

3. FORECAST REASONING.

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

FORECAST DISCUSSION: TYPHOON (TY) 30W HAS REMAINED NEARLY
QUASI-STATIONARY OVER THE PAST 24 HOURS, TRAPPED BETWEEN AN NER TO 
THE SOUTHEAST AND AN STR TO THE NORTHWEST. OVER THE NEXT 24 HOURS, 
THE NER IS FORECAST TO WEAKEN AND DRIFT NORTHWARD, ULTIMATELY MERGING 
WITH THE STR, WHICH IS STRENGTHENING AND EXPANDING EAST. IN RESPONSE 
TO THESE SYNOPTIC ADJUSTMENTS, TY 30W WILL BEGIN A SLOW WESTWARD 
TRANSLATION, ACCELERATING THROUGH TAU 72 AS THE STR CONTINUES TO 
BUILD AND RETROGRADE TO THE WEST. AFTER TAU 72, TY 30W WILL 
DECELERATE IN RESPONSE TO A WEAKNESS IN THE STR INDUCED BY A DEEP 
MID-LATITUDE TROUGH PROGRESSING EAST FROM JAPAN. BY TAU 96, A 
SIGNIFICANT COL REGION WILL DEVELOP BETWEEN THE STR TO THE EAST AND A 
SECOND MID-LEVEL ANTICYCLONE FORMING NEAR TAIWAN AND EXTENDING 
EASTWARD. TY 30W WILL ENTER THIS COL REGION BY TAU 96 AND BECOME 
QUASI-STATIONARY BY TAU 120, THOUGH SIGNIFICANT UNCERTAINTY EXISTS IN 
THE EXACT TIMING, STRUCTURE, AND PLACEMENT OF THE COL REGION. 
REGARDING INTENSITY, ONCE TY 30W BEGINS MOVING WESTWARD, IT WILL 
TRAVERSE A MORE CONDUCIVE ENVIRONMENT CHARACTERIZED BY WARMER 
UNPERTURBED SSTS (MITIGATING UPWELLING EFFECTS) AND AN IMPROVED 
OUTFLOW PATTERN AS IT SEPARATES FROM THE UPPER-LEVEL TROUGH TO THE 
NORTH. THE SYSTEM IS FORECAST TO STEADILY INTENSIFY TO A PEAK OF 125 
KTS BY TAU 36, THEN PLATEAU FOR 24 HOURS DUE TO STRUCTURAL 
ADJUSTMENTS FROM SECONDARY EYEWALL FORMATION. THE SYSTEM WILL THEN 
WEAKEN STEADILY THROUGH THE REMAINDER OF THE FORECAST PERIOD AS IT 
ENCOUNTERS RESTRICTED OUTFLOW ALOFT AND ENHANCED MID-LEVEL EASTERLY 
SHEAR. BY TAU 120, MORE RAPID WEAKENING IS LIKELY AS THE SYSTEM 
BECOMES STATIONARY OVER DIMINISHED OHC WATERS, WITH RAPID SURFACE 
COOLING DUE TO PERSISTENT VERTICAL MIXING AND UPWELLING. 

MODEL DISCUSSION: TRACK GUIDANCE IS IN STRONG AGREEMENT THROUGH THE
BULK OF THE FORECAST PERIOD. CROSS-TRACK SPREAD INCREASES MARGINALLY 
THROUGH TAU 72, WITH SUBSTANTIAL UNCERTAINTY EMERGING AFTER TAU 96 
DUE TO DISCREPANCIES REGARDING THE TIMING AND POSITION OF THE 
EXPECTED COL REGION. IN TERMS OF THE GUIDANCE ENVELOPE, EC-AIFS AND 
AI MODELS ANCHOR THE SOUTHERN EDGE, WHILE NAVGEM AND ECMWF BOUND THE 
NORTHERN EDGE. AFTER TAU 96, ALL MODELS DEPICT A SIGNIFICANT AND 
RAPID DECELERATION, THOUGH SOLUTIONS DIVERGE ON THE DIRECTION OF 
SUBSEQUENT DRIFT: AI MODELS DRIFT THE SYSTEM WESTWARD, WHILE THE BULK 
OF THE DYNAMICAL MODELS SHOW A MORE NORTHWARD OR EASTWARD TRAJECTORY. 
ENSEMBLE MEANS MOSTLY DEPICT A DECELERATION, FOLLOWED BY AN 
ANTICYCLONIC LOOP BEFORE RESUMING A WESTWARD TRACK IN THE EXTENDED 
RANGE. THE JTWC TRACK FORECAST IS POSITIONED ON THE SOUTHERN PORTION 
OF THE GUIDANCE ENVELOPE, CLOSEST TO THE AI CONSENSUS (AICN), THROUGH 
THE FORECAST PERIOD. INTENSITY GUIDANCE SHOWS A WIDE RANGE OF 
POSSIBLE PEAK INTENSITIES, THOUGH THE PACKAGE GENERALLY AGREES ON THE 
TIMING OF THE PEAK BETWEEN TAU 36 AND TAU 60. THE JTWC INTENSITY 
FORECAST IS PLACED ON THE HIGHER END OF THE ENVELOPE, BELOW GOOGLE 
DEEPMIND (GDM), BUT SLIGHTLY HIGHER THAN CTCX THROUGH PEAK INTENSITY. 
FROM TAU 60 ONWARD, THE FORECAST FOLLOWS THE GENERAL DECAY RATE OF 
THE GDM TRACKER. 

FORECAST CONFIDENCE:
   TRACK 00-72 HR: HIGH
   TRACK 72-120 HR: MEDIUM
   INTENSITY 00-72 HR: MEDIUM
   INTENSITY 72-120 HR: LOW//
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