Advisories

WDPN31 PGTW 291500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR SUPER TYPHOON 30W (IN-FA) WARNING NR 
025//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 16.6N 151.3E
   INITIAL INTENSITY: 130 KTS
   GEOGRAPHIC REFERENCE: 328 NM EAST-NORTHEAST OF SAIPAN
   MOVEMENT PAST 6 HOURS: WESTWARD AT 16 KTS
   SIGNIFICANT WAVE HEIGHT: 60 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
IN-FA IS LIKELY AT OR VERY NEAR SUPER TYPHOON (STY) STRENGTH.
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS
CONTINUED COOLING OF CLOUD-TOP TEMPERATURES AND WARMING OF THE
40-NM WIDE EYE. THE EYE HAS WARMED TO +21.8 DEGREES CELSIUS FROM
+17 DEGREES CELSIUS SIX HOURS AGO. THE DISTRIBUTION OF CLOUD-TOP
TEMPERATURES IS VERY UNIFORM. AT 291200Z, THE NARROWEST WIDTHS OF
THE BD-CURVE BLACK AND WHITE SHADES MEASURED APPROXIMATELY 60 NM
AND 30 NM, RESPECTIVELY. A 291013Z METOP-B MHS PASS REVEALED A
THICK RING SURROUNDING THE CENTER THAT LACKED DISTINCT BANDING
FEATURES, SUPPORTING THE ASSESSMENT THAT THE SYSTEM HAS SOME
ANNULAR CHARACTERISTICS. THE ACCOMPANYING ASCAT-B IMAGE INDICATED
THAT THE CORE OF STORM- AND TYPHOON-FORCE WINDS IS RATHER LARGE
WITH RESPECT TO THE EXTENT OF GALE-FORCE WINDS. A 290755Z
SENTINEL-1C SAR PASS ESTIMATED SIMILAR WIND RADII WITH MAXIMUM
WINDS NEAR 120 KTS. SINCE THAT TIME, THE STORM'S SATELLITE
APPEARANCE HAS CONTINUED TO IMPROVE. THE DVORAK EIR EYE TECHNIQUE
YIELDED A DATA T-NUMBER OF 7.0 BY 291300Z. HOWEVER, GIVEN THE EYE
SIZE, THE ACTUAL INTENSITY WOULD LIKELY BE LOWER THAN 140 KTS.
THEREFORE, THE INITIAL INTENSITY HAS BEEN RAISED TO 130 KTS WITH
MEDIUM CONFIDENCE, WHICH IS CLOSEST TO D-MINT AND D-PRINT. THE
INITIAL POSITION IS PLACED WITH HIGH CONFIDENCE BASED ON THE
WELL-DEFINED EYE IN SHORTWAVE IR IMAGERY. THE ENVIRONMENT REMAINS
FAVORABLE, WITH LOW VERTICAL WIND SHEAR (VWS) AND HIGH OCEAN HEAT
CONTENT (OHC).

INITIAL WIND RADII BASIS: SCATTEROMETER AND SAR DATA 

CURRENT STEERING MECHANISM: SOUTHWESTERN FLANK OF A DEEP-LAYER
SUBTROPICAL RIDGE (STR) CENTERED NEAR 28N 165E

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T6.0 - 115 KTS
   RJTD: T6.5 - 127 KTS
   RCTP: T6.0 - 115 KTS
   CIMSS SATCON: 120 KTS AT 290510Z
   CIMSS ADT: 112 KTS AT 291130Z
   CIMSS AIDT: 124 KTS AT 291130Z
   CIMSS D-MINT: 129 KTS AT 291329Z
   CIMSS D-PRINT: 129 KTS AT 291130Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 10-15 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: STY 30W WILL CONTINUE WEST-NORTHWESTWARD ALONG
THE SOUTHWESTERN PERIPHERY OF THE STR THROUGH TAU 36. A BROAD,
LONGWAVE TROUGH PASSING OVER HONSHU WILL INDUCE A LARGE WEAKNESS IN
THE STR, ALLOWING STY 30W TO TURN POLEWARD AND SLOW DOWN. THE
PROGRESSIVE TROUGH WILL RACE DOWNSTREAM, AND A SEPARATE DEEP-LAYER
STR TO THE WEST WILL BUILD EASTWARD, CLOSING OFF THE WEAKNESS AND
CAUSING THE SYSTEM TO DEFLECT WESTWARD. BY THE END OF THE FORECAST
PERIOD, ANOTHER TROUGH PASSING TO THE NORTH MAY CREATE ANOTHER
OPENING, AND THE SYSTEM SHOULD SLOW DOWN AND TURN POLEWARD ONCE
AGAIN. THERE REMAINS A GREAT DEAL OF UNCERTAINTY IN THE TRACK
BEYOND TAU 36. THE INTERACTION OF THE LONGWAVE TROUGH WITH BOTH
RIDGES WILL INFLUENCE THE POLEWARD EXTENT OF THE TRACK PRIOR TO THE
WESTWARD DEFLECTION AND THE TIMING OF THE WESTWARD TURN. IF THE
TROUGH PASSES MORE SLOWLY OR THE STR TO THE EAST CLOSES THE
WEAKNESS MORE SLOWLY, STY 30W COULD TURN NORTHEASTWARD PRIOR TO
DEFLECTING WESTWARD. AN ADDITIONAL SCENARIO EMERGES BY TAU 120. IF
THE SECOND TROUGH IS WEAKER THAN PREDICTED OR THE WESTERN RIDGE
BUILDS MORE STRONGLY, THE SYSTEM COULD CONTINUE STRAIGHT WESTWARD,
DELAYING THE POLEWARD TURN BY 24-48 HOURS OR MORE.

A LITTLE MORE STRENGTHENING IS POSSIBLE WHILE VWS REMAINS LOW AND
OHC REMAINS HIGH OVER THE NEXT 6-12 HOURS. HOWEVER, FROM TAU 12
THROUGH TAU 48, THE SYSTEM WILL MOVE OVER SLIGHTLY LOWER OHC
VALUES, WHICH SHOULD INDUCE SLOW WEAKENING. THE PREDICTED LOW
TRANSLATION SPEED ASSOCIATED WITH THE SHARP WESTWARD TURN WILL
INCREASE THE POTENTIAL FOR COOL WATER UPWELLING. FURTHERMORE,
GLOBAL MODELS DEPICT A BRIEF INCREASE IN MID-LEVEL SHEAR TO 20-30
KTS FROM TAU 48 TO TAU 60, LIKELY ASSOCIATED WITH THE PASSING
TROUGH. THESE FACTORS SHOULD BRING ABOUT A STEADY WEAKENING TREND
AFTER TAU 36. AFTER TAU 60, VWS SHOULD EASE, AND OHC APPEARS TO BE
SUFFICIENTLY HIGH TO SUSTAIN A HIGH-INTENSITY STORM. THE FORECAST
THEREFORE CALLS FOR THE INTENSITY TREND TO LEVEL OFF AT TAU 60.
SIGNIFICANT UNCERTAINTY REMAINS IN THE INTENSITY FORECAST BECAUSE
IT WILL DEPEND ON THE TRACK AND ON HOW THE STORM STRUCTURE CHANGES
AS A RESULT OF THE WEAKENING TREND.

MODEL DISCUSSION: TRACK GUIDANCE REMAINS IN EXCELLENT AGREEMENT
THROUGH TAU 24, WITH A CROSS-TRACK SPREAD OF 50 NM. MODELS DIVERGE
SIGNIFICANTLY AFTER TAU 24, WITH THE BULK OF THE PHYSICS-BASED
MODELS DEPICTING AN ABRUPT WESTWARD TURN AND THE AI MODELS CARRYING
THE SYSTEM NORTHEASTWARD FOR 12-24 HOURS PRIOR TO DEFLECTING IT
WESTWARD. IN THE AI SOLUTIONS, THE SYSTEM REACHES A HIGHER LATITUDE
AND MAKES THE SECOND POLEWARD TURN MUCH EARLIER. MOST OF THE
PHYSICS-BASED MODELS RUN THE SYSTEM ALONG A LONGER WESTWARD TRACK
PRIOR TO TURNING THE SYSTEM NORTHWARD. HAFS-A, GALWEM, AND UKMET DO
NOT DEPICT A POLEWARD TURN UNTIL WELL AFTER TAU 120. THROUGH TAU
24, THE JTWC FORECAST TRACK LIES ALONG THE MULTI MODEL CONSENSUS
(CONW) AT THE CENTER OF THE GUIDANCE ENVELOPE. FROM TAU 24 THROUGH
TAU 72, THE TRACK SLOWLY HEDGES TOWARD THE AI-MODEL MEAN (AICN).
THROUGH TAU 120, THE FORECAST REMAINS BETWEEN AICN TO THE NORTH AND
CONW TO THE SOUTH. INTENSITY GUIDANCE IS TIGHT THROUGH TAU 60,
DEPICTING SLOW TO STEADY WEAKENING. HAFS-A THEN DEPICTS
REINTENSIFICATION TO 135 KTS BY TAU 120. GOOGLE DEEPMIND IS CLOSER
TO THE CENTER OF THE GUIDANCE ENVELOPE BUT DEPICTS WEAKENING AFTER
TAU 72 BECAUSE IT RECURVES THE SYSTEM INTO THE WESTERLIES MORE
QUICKLY. COAMPS-TC, THE FASTEST MODEL TO RECURVE THE STORM, SHOWS
STEADY WEAKENING TO 75 KTS. THE JTWC INTENSITY FORECAST IS SET NEAR
THE CENTER OF THE GUIDANCE ENVELOPE THROUGH TAU 120, OWING TO A
GENERALLY FAVORABLE ENVIRONMENT THAT SUPPORTS MAINTENANCE OF A
100-KT SYSTEM ALONG THE FORECAST TRACK.

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