Advisories

WDPN31 PGTW 021500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 30W (IN-FA) WARNING NR 041//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 23.0N 140.2E
   INITIAL INTENSITY: 65 KTS
   GEOGRAPHIC REFERENCE: 124 NM SOUTH-SOUTHWEST OF IWO TO
   MOVEMENT PAST 6 HOURS: WEST-NORTHWESTWARD AT 08 KTS
   SIGNIFICANT WAVE HEIGHT: 30 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED SHORTWAVE INFRARED (SWIR) SATELLITE IMAGERY DEPICTS A FULLY 
EXPOSED LOW-LEVEL CIRCULATION CENTER (LLCC), WITH FRAGMENTED, 
MODERATE CONVECTION RE-DEVELOPING ALONG THE REMNANT EYEWALL AT A 
RADIUS OF APPROXIMATELY 50 NM FROM THE LLCC. A 020811Z SSMIS 89-GHZ 
MICROWAVE PASS REVEALED A WELL-DEFINED LLCC ACCOMPANIED BY A 
FRAGMENTED REMNANT EYEWALL, WITH THE MOST ORGANIZED CONVECTIVE 
BANDING CONCENTRATED WITHIN THE NORTHERN SEMICIRCLE OF THE 
CIRCULATION. THE MICROWAVE IMAGERY ALSO DEPICTED A BROAD EXPANSE OF 
MID-TROPOSPHERIC DRY AIR TO THE NORTHWEST, ALONG AND BEHIND AN 
APPROACHING BAROCLINIC COLD-FRONTAL BOUNDARY CURRENTLY POSITIONED 
APPROXIMATELY 475 NM TO THE NORTHWEST OF TYPHOON (TY) 30W. IN THE 
UPPER LEVELS, ATMOSPHERIC MOTION VECTORS (AMVS) AND JTWC STREAMLINE 
ANALYSIS DEPICT AN UPPER-TROPOSPHERIC POINT SOURCE DIRECTLY 
OVERLAYING TY 30W AND A 200-HPA ANTICYCLONIC CIRCULATION JUST EAST OF 
THE VORTEX, WHICH SUSTAINS A VIGOROUS POLEWARD OUTFLOW CHANNEL. THE 
INITIAL POSITION IS ASSESSED WITH HIGH CONFIDENCE BASED ON THE 
UNOBSCURED LLCC IN THE SWIR IMAGERY. THE INITIAL INTENSITY IS 
ASSESSED WITH LOW CONFIDENCE, WEIGHTED AT THE UPPER BOUND OF THE 
AVAILABLE ESTIMATES OUTLINED BELOW BASED ON TEMPORAL EXTRAPOLATION OF 
AN EARLIER ASCAT ULTRA-HIGH RESOLUTION (UHR) RETRIEVAL, WHICH 
SUPPORTS A HIGHER SURFACE VORTEX INTENSITY THAN DVORAK-BASED 
ESTIMATES INDICATE. ENVIRONMENTAL CONDITIONS ARE MARGINALLY 
FAVORABLE, PARTICULARLY NOW THAT THE SYSTEM HAS EMERGED FROM ITS 
UPWELLED COLD WAKE. THE PRIMARY INHIBITING FACTOR REMAINS THE 
MODERATE NORTHWESTERLY MID-LEVEL VERTICAL WIND SHEAR (VWS).

INITIAL WIND RADII BASIS: PERSISTENCE 

CURRENT STEERING MECHANISM: TY 30W IS EMBEDDED IN A WEAK, COMPETING 
STEERING REGIME WITHIN A COL REGION BETWEEN SUBTROPICAL RIDGE (STR) 
CENTERS TO THE EAST AND WEST. 

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T4.0 - 65 KTS
   RJTD: T3.5 - 55 KTS
   RCTP: T3.5 - 55 KTS
   CIMSS SATCON: 57 KTS AT 020930Z
   CIMSS ADT: 43 KTS AT 021130Z
   CIMSS AIDT: 56 KTS AT 021130Z
   CIMSS D-PRINT: 50 KTS AT 021130Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 5-10 KTS
   SST: 28-29 CELSIUS
   OUTFLOW: STRONG POLEWARD
   OTHER FACTORS: MODERATE NORTH-NORTHWESTERLY MID-LEVEL SHEAR. 

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

3. FORECAST REASONING.

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

FORECAST DISCUSSION: TY 30W REMAINS EMBEDDED WITHIN A BROAD COL 
REGION BETWEEN STR CENTERS TO THE EAST AND WEST. THE BROADER SYNOPTIC 
RIDGE COMPLEX HAS BEEN RETROGRADING SLOWLY WESTWARD WHILE MAINTAINING 
ITS RELATIVE POSITIONAL GEOMETRY, THOUGH THIS WESTWARD RETROGRESSION 
IS NEARING ITS ZONAL INFLECTION POINT. THE SYNOPTIC STEERING PATTERN 
IS POISED TO UNDERGO A STRUCTURAL RECONFIGURATION, AND TY 30W WILL 
DECELERATE ONCE MORE AS THE STEERING GRADIENT EVOLVES AROUND IT. A 
SERIES OF TRANSIENT MID-LATITUDE SHORTWAVE TROUGHS IS BEGINNING TO 
PASS TO THE NORTH AND WILL GRADUALLY ERODE THE NORTHEASTERN PERIPHERY 
OF THE WESTERN RIDGE OVER THE NEXT 24 HOURS, ALLOWING TY 30W TO 
GRADUALLY RECURVE POLEWARD WHILE MAINTAINING A SLOW TRANSLATION 
SPEED. BY TAU 36, THE WESTERN RIDGE WILL HAVE ERODED AND RETROGRADED 
SUFFICIENTLY TO ALLOW THE EASTERN RIDGE TO ASSUME THE DOMINANT 
STEERING INFLUENCE. AFTER TAU 36, THE WESTERN PERIPHERY OF THE 
EASTERN RIDGE WILL REORIENT ALONG A MORE MERIDIONAL AXIS, STEERING TY 
30W POLEWARD ALONG ITS WESTERN PERIPHERY. BY TAU 48, TY 30W WILL 
CREST THE STR AXIS AND BEGIN TO ACCELERATE NORTHEASTWARD. AFTER TAU 
60, THE SYSTEM WILL RAPIDLY ACCELERATE TO TRANSLATION SPEEDS 
EXCEEDING 30 KTS AS IT EMBEDS WITHIN THE BAROCLINIC MID-LATITUDE 
WESTERLIES. REGARDING INTENSITY, THE INITIAL STAGES OF RE-
INTENSIFICATION HAVE ALREADY COMMENCED, AS NASCENT DEEP CONVECTION IS 
RE-DEVELOPING ALONG THE REMNANT EYEWALL. THE SYSTEM WILL CONTINUE TO 
GRADUALLY INTENSIFY OVER THE NEXT 36 HOURS, THOUGH THE EXPANSIVE 
RADIUS OF MAXIMUM WINDS (RMW) WILL MODERATE THE RATE OF SPIN-UP AND 
CAP THE POTENTIAL PEAK INTENSITY. THE OFFICIAL FORECAST CALLS FOR A 
PEAK INTENSITY OF 75 KTS, THOUGH 80 KTS IS ATTAINABLE DEPENDING ON 
HOW RAPIDLY THE INNER-CORE CONVECTIVE STRUCTURE RECONSOLIDATES. BY 
TAU 48, HOWEVER, A RENEWED SURGE OF MID-LEVEL WESTERLY VWS AND MID-
TROPOSPHERIC DRY AIR ENTRAINMENT WILL PENETRATE THE INNER CORE, 
INDUCING RAPID VORTEX TILT AND VERTICAL DECOUPLING BY TAU 60. TY 30W 
WILL SUBSEQUENTLY WEAKEN STEADILY THROUGH THE REMAINDER OF THE 
FORECAST PERIOD, THOUGH THE RATE OF SPIN-DOWN WILL BE PARTIALLY 
MITIGATED BY NON-TROPICAL BAROCLINIC FORCING AS THE SYSTEM UNDERGOES 
EXTRATROPICAL TRANSITION (ETT) FROM TAU 72 TO TAU 96. 

MODEL DISCUSSION: TRACK GUIDANCE IS IN GOOD CROSS-TRACK AGREEMENT 
THROUGH THE MAJORITY OF THE FORECAST PERIOD, WITH CROSS-TRACK 
DISPERSION GRADUALLY INCREASING TO 100 NM AT TAU 72 AND 250 NM AT TAU 
96. THE GFS, GEFS, AND NAVGEM ARE POSITIONED ALONG THE EASTERN 
PERIPHERY OF THE GUIDANCE ENVELOPE, WHILE THE ECMWF-AIFS, UKMET 
(EGRR), AND GOOGLE DEEPMIND (GDM) ARE POSITIONED ALONG THE WESTERN 
PERIPHERY. ALONG-TRACK SPREAD IS MUCH MORE PRONOUNCED, PARTICULARLY 
AFTER TAU 60 ONCE THE SYSTEM BEGINS TO ACCELERATE NORTHEASTWARD INTO 
THE MID-LATITUDE WESTERLIES. BY TAU 72, ALONG-TRACK SPREAD BETWEEN 
THE SLOWER NAVGEM AND THE FASTER ECMWF-AIFS EXCEEDS 250 NM, DIVERGING 
FURTHER TO OVER 700 NM BY TAU 96. THE OFFICIAL JTWC TRACK FORECAST IS 
POSITIONED NEAR THE SELECTIVELY FILTERED CONSENSUS MEAN (TES1) 
THROUGH THE FORECAST PERIOD, SLIGHTLY EAST OF AND SLOWER THAN THE AI 
CONSENSUS (AICN). ALL COUPLED OCEAN-ATMOSPHERE MESOSCALE INTENSITY 
GUIDANCE, AS WELL AS THE GFS- AND NAVGEM-DRIVEN SHIPS GUIDANCE, 
DEPICT A GRADUAL RE-INTENSIFICATION TO A PEAK BETWEEN 75 AND 80 KTS 
AT TAUS 36-48, FOLLOWED BY STEADY WEAKENING THROUGH THE REMAINDER OF 
THE FORECAST PERIOD. THE OFFICIAL JTWC INTENSITY FORECAST IS ALIGNED 
CLOSELY WITH THIS GUIDANCE CLUSTER THROUGH THE FORECAST PERIOD. 

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