Advisories

WDPN31 PGTW 301500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 30W (IN-FA) WARNING NR 029//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 19.7N 144.5E
   INITIAL INTENSITY: 120 KTS
   GEOGRAPHIC REFERENCE: 87 NM NORTHWEST OF AGRIHAN
   MOVEMENT PAST 6 HOURS: WEST-NORTHWESTWARD AT 19 KTS
   SIGNIFICANT WAVE HEIGHT: 58 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
THE SATELLITE APPEARANCE OF TYPHOON (TY) 30W HAS REMAINED QUITE
STABLE OVER THE PAST SIX HOURS IN ANIMATED ENHANCED INFRARED (EIR)
SATELLITE IMAGERY. THE AVERAGE CDO CLOUD TOP TEMPERATURES HAVE
WARMED A FEW DEGREES, AND THE 40-NM WIDE EYE HAS COOLED BY ONLY 1
DEGREE TO +19 DEGREES CELSIUS. THE CONVECTIVE STRUCTURE IS STILL
QUASI-ANNULAR IN NATURE, AN ASSESSMENT SUPPORTED BY A 300640Z SSMIS
PASS, WHICH REVEALED A VERY IMPRESSIVE SOLID RING WITH A SMALL
CONVECTIVE BAND TO THE SOUTH. A 300832Z RCM-1 SAR PASS ESTIMATED
MAXIMUM WINDS OF 125 KTS ALONG THE NORTHERN AND EASTERN SIDE OF THE
EYEWALL AND WIND RADII VIRTUALLY UNCHANGED FROM PRIOR UHR
SCATTEROMETER DATA. STORM- AND TYPHOON-FORCE WINDS OCCUPY AN
UNUSUALLY LARGE AREA BENEATH THE CDO. BASED ON THE SAR DATA AND
RECENT TRENDS, THE INITIAL INTENSITY HAS BEEN LOWERED TO 120 KTS
WITH MEDIUM CONFIDENCE. THE INITIAL POSITION IS PLACED WITH HIGH
CONFIDENCE BASED ON THE WELL-DEFINED EYE. THE ENVIRONMENT REMAINS
FAVORABLE, WITH LOW VERTICAL WIND SHEAR (VWS), OCEAN HEAT CONTENT
(OHC) VALUES AROUND 80-100 KJ PER CM2, AND MODERATE RADIAL OUTFLOW
ALOFT.

INITIAL WIND RADII BASIS: SCATTEROMETER AND SAR DATA 

CURRENT STEERING MECHANISM: SOUTHWESTERN FLANK OF A DEEP-LAYER
SUBTROPICAL RIDGE (STR) CENTERED NEAR 29N 163E

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T6.5 - 127 KTS
   RJTD: T6.5 - 127 KTS
   RCTP: T6.0 - 115 KTS
   CIMSS ADT: 102 KTS AT 301200Z
   CIMSS AIDT: 128 KTS AT 301200Z
   CIMSS D-MINT: 123 KTS AT 301135Z
   CIMSS D-PRINT: 125 KTS AT 301200Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 5-10 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: MODERATE RADIAL

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: TY 30W WILL CONTINUE NORTHWESTWARD AND BEGIN
ROUNDING THE SOUTHWESTERN PERIPHERY OF THE STR, RESULTING IN A
POLEWARD TURN OVER THE NEXT 12 HOURS. A PROGRESSIVE LONGWAVE TROUGH
PASSING OVER HONSHU HAS CREATED A LARGE WEAKNESS IN THE STR, AND
CONSEQUENTLY THE SYSTEM WILL SLOW DOWN AS IT ENTERS THE AREA OF
COMPETING STEERING INFLUENCES. BY TAU 24, THE TROUGH AXIS WILL BE
DUE NORTH OF THE VORTEX, AND THE SYSTEM WILL BEGIN TO TURN
NORTHEASTWARD. HOWEVER, THE TROUGH WILL BE MOVING FAST, AND WITH A
SEPARATE STR BUILDING WESTWARD AND RAPIDLY CLOSING THE WEAKNESS, TY
30W SHOULD TURN WEST-SOUTHWESTWARD UNDER THE STEERING INFLUENCE OF
THE SOUTHEASTERN FLANK OF THE STR. NEAR TAU 72, ANOTHER TROUGH
PASSING THROUGH HONSHU WILL WEAKEN THE STR, ALLOWING TY 30W TO MAKE
THE FINAL POLEWARD TURN. BY TAU 120, THE SYSTEM SHOULD BEGIN
ACCELERATING NORTH-NORTHEASTWARD ALONG THE NORTHWESTERN PERIPHERY
OF THE RIDGE TO THE SOUTHEAST. THE JTWC TRACK CONFIDENCE IS LOW
BECAUSE LARGE UNCERTAINTY REMAINS IN THE EVOLUTION OF THESE
SYNOPTIC-SCALE FEATURES, AS WELL AS THE PRECISE LOCATION OF TY 30W
WHEN THE LONGWAVE TROUGH SWEEPS THROUGH. THIS UNCERTAINTY IS
REFLECTED IN 530 NM OF TRACK-GUIDANCE SPREAD AT TAU 120.

THE VORTEX WILL MOVE OVER SLIGHTLY HIGHER OHC SHORTLY, WHILE VWS
REMAINS LOW. THESE FACTORS WILL HELP KEEP THE INTENSITY STEADY
THROUGH TAU 12. THE QUASI-ANNULAR STRUCTURE OFTEN SUPPORTS
PERSISTENCE OF SHORT-TERM INTENSITY, MAKING IT MORE LIKELY TO
REMAIN INTENSE AND WEAKEN MORE SLOWLY. AFTER TAU 12, THE FORWARD
SPEED WILL DECREASE CONSIDERABLY, AND THE POTENTIAL FOR SIGNIFICANT
UPWELLING OF COOLER WATER INCREASES. BY TAU 36, THE LONGWAVE TROUGH
PASSING TO THE NORTH WILL INDUCE 20-30 KTS OF MID-LEVEL
NORTHEASTERLY SHEAR. ACCORDINGLY, THE FORECAST CALLS FOR STEADY
WEAKENING DURING THIS TIME. THESE CONDITIONS WILL IMPROVE BY TAU
60, WHEN VWS WILL EASE, AND THE SYSTEM WILL MOVE AWAY FROM ITS COLD
WAKE. THE INTENSITY TREND SHOULD LEVEL OFF BEFORE THE SYSTEM
RECURVES POLEWARD AGAIN BY TAU 72 AND ENCOUNTERS OHC VALUES
APPROACHING ZERO. THEREFORE, GRADUAL WEAKENING IS INDICATED FOR THE
LATTER PART OF THE FORECAST. BECAUSE THE TRACK WILL IMPACT
INTENSITY, THE INTENSITY FORECAST IS ALSO ASSESSED WITH LOW
CONFIDENCE.

MODEL DISCUSSION: TRACK GUIDANCE IS TIGHT FOR THE FIRST 12 HOURS
AND THEN DIVERGES. BY NOW, MOST SOLUTIONS SHOW A TURN TOWARD THE
NORTHEAST FOLLOWED BY A WEST-SOUTHWESTWARD DEFLECTION. THE
REMAINING UNCERTAINTY LIES IN THE AMOUNT OF NORTHEASTWARD DISTANCE
TRAVELED BEFORE THE DEFLECTION OCCURS. A FARTHER NORTHEASTWARD
TRACK WOULD CARRY THE SYSTEM TO A HIGHER LATITUDE, CLOSER TO THE
MID-LATITUDE WESTERLIES, AND OVER LOWER OHC. GOOGLE DEEPMIND AND
AIFS ARE THE MOST NORTHEASTWARD SOLUTIONS, WHICH RESULT IN A
QUICKER SUBSEQUENT POLEWARD TURN AT TAU 96 AND TAU 120 AND A FASTER
RATE OF WEAKENING. COAMPS-TC AND HAFS-A ARE AT THE OTHER END OF THE
SPECTRUM, SHOWING AN ALMOST IMMEDIATE WESTWARD DEFLECTION FOLLOWED
BY A VERY SLOW POLEWARD TURN. THESE SOLUTIONS DEPICT
REINTENSIFICATION ONCE THE SYSTEM MOVES AWAY FROM ITS COLD WAKE.
THE JTWC FORECAST TRACK IS POSITIONED NEAR THE AI-MODEL MEAN
(AICN), REPRESENTING AN INTERMEDIATE TRACK SCENARIO BETWEEN THE
MOST NORTHEASTWARD DEEPMIND AND AIFS SOLUTIONS AND THE MORE
WESTWARD COAMPS-TC AND HAFS-A SOLUTIONS. THE FORECAST LEANS CLOSER
TO DEEPMIND THAN TO HAFS-A. THE JTWC INTENSITY FORECAST REFLECTS
THIS INTERMEDIATE SCENARIO, HOLDING SLIGHTLY STRONGER THAN DEEPMIND
BUT WEAKER THAN COAMPS-TC.

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