Advisories

WDPN33 PGTW 272100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 20W (TWENTY) WARNING NR 
007//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 17.5N 164.1E
   INITIAL INTENSITY: 55 KTS
   GEOGRAPHIC REFERENCE: 179 NM SOUTHWEST OF WAKE ISLAND
   MOVEMENT PAST 6 HOURS: EAST-NORTHEASTWARD AT 08 KTS
   SIGNIFICANT WAVE HEIGHT: 20 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS AN 
EXTREMELY COMPACT SYSTEM, WITH PERSISTENT DEEP CONVECTION CONTINUING 
TO DEVELOP IN AND AROUND THE ASSESSED LOW LEVEL CIRCULATION CENTER 
(LLCC). A DISTINCT, IF VERY SMALL, MICROWAVE EYE FEATURE WAS OBSERVED 
IN BOTH A 271415Z AMSR3 AND 271438Z AMSR2 COLOR-ENHANCED 37GHZ 
MICROWAVE IMAGES. DEEP CONVECTION AT THAT TIME WAS DISPLACED TO THE 
NORTHERN FLANK OF THE LLCC, AND THIS ORIENTATION IS ASSUMED TO REMAIN 
IN PLACE IN LIGHT OF THE PERSISTENCE OF LIGHT SOUTHERLY SHEAR. UPPER-
LEVEL ANALYSIS SHOWS THE SYSTEM POSITIONED JUST WEST OF A 200MB 
ANTICYCLONE, WHICH IS PROVIDING FOR BOTH LOW DEEP-LAYER SHEAR AND 
STRONG POLEWARD OUTFLOW ALOFT, HELPING TO SUSTAIN THE REMARKABLE 
BURST IN INTENSIFICATION SEEN OVER THE PAST 12 HOURS. THE INITIAL 
POSITION IS ASSESSED WITH MEDIUM CONFIDENCE BASED ON AN EXTRAPOLATION 
OF THE MICROWAVE EYE FEATURE SEEN IN THE MICROWAVE IMAGERY DISCUSSED 
ABOVE. THE INITIAL INTENSITY IS ASSESSED WITH MEDIUM CONFIDENCE AS 
WELL. THE BULK OF BOTH THE OBJECTIVE AND SUBJECTIVE INTENSITY 
ESTIMATES ARE STRUGGLING TO ACCURATELY ESTIMATE THE INTENSITY DUE TO 
THE EXTREMELY COMPACT STRUCTURE. THE RAW ADT OF T3.6 IS MOST LIKELY
CLOSEST TO REALITY BASED ON PERSISTENCE WITH THE SAR DATA FROM LAST 
NIGHT WHICH SHOWED 50-55 KNOT WINDS ALREADY AT THAT POINT. 
ENVIRONMENTAL CONDITIONS ARE FAVORABLE TO HIGHLY FAVORABLE, WITH LOW 
SHEAR, ROBUST OUTFLOW ALOFT, WARM SSTS AND IN ADDITION, THE SYSTEM IS 
CROSSING OVER A PATCH OF VERY HIGH OHC WATERS WITH VALUES EXCEEDING 
120 KJ PER CM2.

INITIAL WIND RADII BASIS: PERSISTENCE WITH EARLIER SAR AND
SCATTEROMETER DATA. 

CURRENT STEERING MECHANISM: NORTHERN FLANK OF A DEEP-LAYER RIDGE
COMPLEX WHICH EXTENDS FROM SOUTH OF GUAM NORTHEAST TO A POSITION
EAST OF TS 21W. 

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.5 - 35 KTS
   RJTD: T1.5 - 25 KTS
   KNES: T2.5 - 35 KTS
   PHFO: T2.5 - 35 KTS
   CIMSS SATCON: 45 KTS AT 271435Z
   CIMSS ADT: 51 KTS AT 271730Z
   CIMSS AIDT: 42 KTS AT 271730Z
   CIMSS D-MINT: 33 KTS AT 271436Z
   CIMSS D-PRINT: 36 KTS AT 271800Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 5-10 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: STRONG POLEWARD
   OTHER FACTORS: EXTREMELY COMPACT SIZE OF THE CIRCULATION. 

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

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: THE FORECAST HAS BEEN EXTENDED TO 120
HOURS AND THE MAXIMUM INTENSITY HAS INCREASED SIGNIFICANTLY. 

FORECAST DISCUSSION: TROPICAL STORM (TS) 20W (TWENTY) HAS PUT ON
QUITE THE SHOW OVER THE PAST 12 HOURS, UNEXPECTEDLY UNDERGOING RAPID 
INTENSIFICATION, FROM 30 KNOTS TO 55 KNOTS PRESENTLY. THE SYSTEM IS 
TRACKING EAST-NORTHEASTWARD ALONG THE NORTHERN FLANK OF A BROAD 
REGION OF TROFING WHICH EXTENDS FROM SOUTH OF GUAM ALL THE WAY UP THE 
EASTERN SIDE OF BOTH TS 2OW AND TS 21W FURTHER TO THE NORTHEAST. OVER 
THE NEXT 24 TO 36 HOURS, THE NORTHEASTERN PORTION OF THIS RIDGE WILL 
BUILD AND COME TO DOMINATE THE STEERING FOR TS 20W THROUGH TAU 60. 
AFTER TAU 60, TWO FACTORS COME INTO PLAY TO MAKE THE TRACK MORE 
UNCERTAIN. FIRST AND FOREMOST, TS 20W WILL BEGIN DIRECT BINARY 
INTERACTION WITH TS 21W AND COMMENCE A FUJIWHARA MOTION, WHILE 
SIMULTANEOUSLY THE TWO SYSTEMS TOGETHER MOVE INTO A GENERALLY WEAK 
STEERING PATTERN. THE FORECAST CALLS FOR TS 20W TO TRACK NORTHWARD 
FROM TAU 36 TO TAU 60, THEN TURN NORTHWESTWARD AS TS 21W TRACKS BY TO 
THE SOUTHWEST. THE CURRENT FORECAST CALLS FOR TS 20W TO UNDERGO A 
BRIEF FUJIWHARA WITH 21W BEFORE BEING EJECTED TO THE NORTHEAST BY TAU 
120, THOUGH THE EXTENT OF THE FUJIWHARA IS HIGHLY UNCERTAIN AT THIS 
POINT IN TIME AND THE SYSTEMS COULD UNDERGO A MUCH STRONGER 
INTERACTION. WHILE UNDERGOING BINARY INTERACTION, TS 20W WILL ALSO 
BEGIN SUBTROPICAL TRANSITION (STT) BY TAU 96. REGARDING INTENSITY, 
THE SYSTEM HAS CLEARLY OUTPERFORMED NEARLY ALL GUIDANCE AND 
EXPECTATIONS. HIGHLY FAVORABLE ENVIRONMENTAL CONDITIONS ARE EXPECTED 
TO PERSIST FOR THE NEXT 36 HOURS, AND WILL ALLOW FOR 20W TO CONTINUE 
RAPIDLY INTENSIFYING UP TO AT LEAST 85 KNOTS BEFORE INCREASING SHEAR 
AND DRY AIR ENTRAINMENT WILL CONSPIRE TO WEAKEN THE SYSTEM THROUGH 
THE REMAINDER OF THE FORECAST PERIOD. 

MODEL DISCUSSION: TRACK GUIDANCE IS HIGHLY UNCERTAIN, ESPECIALLY
AFTER TAU 60. CROSS-TRACK SPREAD INCREASES TO NEARLY 1000NM BY TAU 
120, BETWEEN THE NAVGEM AND GALWEM WHICH TRACK THE SYSTEM SLOWLY
WESTWARD AFTER TAU 72 AND THE GEFS MEAN WHICH RAPIDLY TRACKS THE 
SYSTEM NORTHEASTWARD IN THE MID-LATITUDE WESTERLIES. THE AI MODELS, 
AS WELL AS THE GFS ARE CLUSTERED ON THE EASTERN FLANK OF THE GUIDANCE 
ENVELOPE, WHILE THE CONSENSUS, ECENS AND MOGREPS ARE POSITIONED DOWN 
THE MIDDLE. THE JTWC FORECAST IS PLACED NEAR THE AI CONSENSUS MEAN, 
ON THE EASTERN EDGE OF THE ENVELOPE, WITH LOW CONFIDENCE. INTENSITY 
GUIDANCE ALSO DISPLAYS A LARGE AMOUNT OF UNCERTAINTY. NEARLY EVERY 
RAPID INTENSIFICATION (RI) AID HAS TRIGGERED, AND ONLY THE SHIPS-
NAVGEM AND GFS DEPICT AN INTENSITY BELOW 80 KNOTS. THE JTWC FORECAST 
IS PLACED NEAR THE NON-RI INFLUENCED CONSENSUS MEAN THROUGH TAU 36 
WITH LOW CONFIDENCE, AND IN LIGHT OF THE VAST NUMBER OF RI AIDS 
TRIGGERING, IT IS NOT OUT OF THE REALM OF POSSIBILITY THAT THE SYSTEM 
COULD REACH 100 KNOTS OR MORE WITHIN THE NEXT 36 HOURS. HOWEVER, 
AFTER TAU 36, ALL MODELS INDICATE RAPID AND STEADY WEAKENING THROUGH 
THE REMAINDER OF THE FORECAST PERIOD. 

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