Advisories

WDPN33 PGTW 262100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 20W (TWENTY) 
WARNING NR 003//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 17.2N 161.0E
   INITIAL INTENSITY: 30 KTS
   GEOGRAPHIC REFERENCE: 343 NM WEST-SOUTHWEST OF WAKE ISLAND
   MOVEMENT PAST 6 HOURS: EASTWARD AT 01 KTS
   SIGNIFICANT WAVE HEIGHT: 12 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS AN EXTREMELY
COMPACT AND DISORGANIZED SYSTEM, WITH A PARTIALLY EXPOSED LOW LEVEL
CIRCULATION CENTER (LLCC) DISPLACED TO THE SOUTH OF FLARING DEEP 
CONVECTION AND ASSOCIATED MID-LEVEL MESOVORTEX. A 261524Z AMSR2 36GHZ 
IMAGE REVEALED THE COMPACT LLCC EXPOSED ON THE SOUTHERN EDGE OF A 
WEDGE OF LINEAR CONVECTION EXTENDING NORTHWARD. BASED ON COMPARISON OF 
THE AMSR2 IMAGERY AND THE EARLIER ASCAT DATA, THE SYSTEM HAS REMAINED 
QUASI-STATIONARY SINCE 1200Z. THE INITIAL POSITION IS ASSESSED WITH 
HIGH CONFIDENCE BASED ON THE AMSR2 DATA AND ANIMATED MSI. THE INITIAL 
INTENSITY IS ASSESSED WITH MEDIUM CONFIDENCE BASED ON A BLEND OF THE 
AVAILABLE SUBJECTIVE AND OBJECTIVE INTENSITY ESTIMATES NOTED BELOW. 
THE ENVIRONMENT IS MARGINALLY FAVORABLE, CHARACTERIZED BY LOW DEEP-
LAYER WIND SHEAR, MODERATE POLEWARD OUTFLOW ALOFT, AND WARM SSTS WITH 
HIGH OHC. THE SYSTEM IS APPROXIMATELY 415NM SOUTHWEST OF INVEST 91W 
AND UNDERGOING THE INITIAL PHASE OF BINARY INTERACTION. THE TWO 
SYSTEMS ARE INTER-CONNECTED WITHIN A 1009MB CLOSED OUTER ISOBAR. THE 
TWO ARE ALSO INTERTWINED ALOFT, WITH 20W POSITIONED IN THE 
SOUTHWESTERN END OF AN ELONGATED UPPER-LEVEL ANTICYCLONE CENTERED 
ROUGHLY IN THE VICINITY OF INVEST 91W.

INITIAL WIND RADII BASIS: NOT APPLICABLE (THERE ARE NO INITIAL WIND
RADII).

CURRENT STEERING MECHANISM: WEAK STEERING ENVIRONMENT; WEAK BAND OF
LOW-LEVEL SOUTHWESTERLIES ALONG THE NORTHWESTERN PERIPHERY OF A NEAR 
EQUATORIAL RIDGE (NER) AND BINARY INTERACTION WITH INVEST 91W TO THE 
NORTHEAST. 

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T1.5 - 25 KTS
   RJTD: T1.0 - 25 KTS
   KNES: T2.0 - 30 KTS
   PHFO: T2.5 - 35 KTS
   CIMSS SATCON: 34 KTS AT 261720Z
   CIMSS ADT: 34 KTS AT 261740Z
   CIMSS AIDT: 32 KTS AT 261740Z
   CIMSS D-MINT: 22 KTS AT 261751Z
   CIMSS D-PRINT: 22 KTS AT 261800Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE
   VWS: 5-10 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: MODERATE POLEWARD
   OTHER FACTORS: EXTREMELY COMPACT NATURE OF THE SYSTEM AND THE
INFLUENCE OF THE BINARY INTERACTION WITH 91W. 

ANALYSIS CONFIDENCE:
   INITIAL POSITION: HIGH
   INITIAL INTENSITY: MEDIUM
   INITIAL WIND RADII: NOT APPLICABLE

3. FORECAST REASONING.

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

FORECAST DISCUSSION: TROPICAL DEPRESSION (TD) 20W HAS MOVED LITTLE IN 
THE PAST SIX HOURS, CURRENTLY TRAPPED IN A WEAK AND COMPETING STEERING 
ENVIRONMENT. OVER THE NEXT 12 TO 24 HOURS, TD 20W WILL TRACK SLOWLY 
EASTWARD ALONG THE NORTH SIDE OF THE WEAK NER TO THE SOUTHEAST. AFTER 
TAU 24, THE NER IS EXPECTED TO RECEDE EQUATORWARD, WHILE A NOSE OF THE 
STR TO THE NORTHEAST PUSHES SOUTHWARD TO THE EAST OF BOTH 20W AND 91W. 
THE COMBINATION OF A STRENGTHENING GRADIENT ON THE EASTERN SIDE OF TD 
20W AND THE INFLUENCE OF THE BINARY INTERACTION WITH 91W, WILL PUSH TD 
20W NORTHWARD THROUGH THE REMAINDER OF THE FORECAST PERIOD. REGARDING 
INTENSITY, THE SYSTEM WILL REMAIN STAGNANT OR INTENSIFY ONLY SLIGHTLY 
OVER THE COURSE OF THE NEXT 24 HOURS DUE TO THE CONTINUED INFLUENCE OF 
MODERATE MID-LEVEL SOUTHERLY SHEAR AND A RELATIVELY WEAK OUTFLOW 
ENVIRONMENT ALOFT. BY TAU 36, AS 91W MOVES RAPIDLY NORTHWARD INTO A 
BAND OF UNFAVORABLE CONDITIONS ALOFT, 20W WILL HAVE AN OPPORTUNITY TO
INTENSIFY MORE RAPIDLY AS IT REMAINS IN A REGION OF LIGHT SHEAR AND
MODERATE POLEWARD OUTFLOW. 20W STEADILY INTENSIFIES TO A PEAK OF 60 
KNOTS BY TAU 60 BEFORE IT TOO SUCCUMBS TO INCREASING SHEAR AND DRY AIR 
ENTRAINMENT, AND BEGINS TO WEAKEN THROUGH THE REMAINDER OF THE 
FORECAST. THAT IS FORECAST DOOR NUMBER ONE. BEHIND DOOR NUMBER TWO 
LIES AN ALTERNATE SCENARIO, ONE THAT SEES TD 20W DISSIPATED WITHIN THE 
NEXT 24 HOURS. AS DEPICTED BY THE ECMWF, INVEST 91W MOVES NORTHWARD AT 
A MUCH SLOWER PACE, WHILE TD 20W MOVES EAST-NORTHEASTWARD AT A FASTER 
PACE. THIS RESULTS IN TD 20W BECOMING ABSORBED WITHIN THE MUCH LARGER 
WIND FIELD ASSOCIATED WITH 91W AS IT TRACKS SLOWLY NORTHWARD. AT THIS 
POINT, THE VAST MAJORITY OF MODEL GUIDANCE SUPPORTS THE CURRENT 
FORECAST WITH ONLY THE ECMWF AND GOOGLE DEEPMIND SUPPORTING THE 
ALTERNATE SCENARIO. HOWEVER, IT CANNOT BE DISMISSED ENTIRELY AND WILL 
BE CLOSELY MONITORED. 

MODEL DISCUSSION: TRACK GUIDANCE IS MIXED. AS DISCUSSED ABOVE, THE
MAJORITY OF THE MODEL GUIDANCE DEPICTS A NORTHEASTWARD TRACK THROUGH 
TAU 24, THEN A TURN NORTHWARD THROUGH THE REMAINDER OF THE FORECAST. 
THE ECMWF AND FNV3 ARE THE TWO MODELS SUPPORTING AN EASTWARD 
TRAJECTORY FOR JUST 24 HOURS, BEFORE DISSIPATING THE SYSTEM. THE GFS 
OFFERS A MIDDLE-ROAD SOLUTION, EJECTING NORTHEASTWARD AFTER TAU 48 AND 
APPROACHING THE DATELINE BY TAU 120. THE PRIMARY GUIDANCE ENVELOPE 
(DISREGARDING GFS, ECMWF AND FNV3) DISPLAYS A 140NM CROSS-TRACK 
SPREAD, WHICH INCREASES TO 230NM BY TAU 120. ALONG-TRACK SPREAD 
INCREASES SHARPLY AFTER TAU 48, TO 350NM BY THE END OF THE FORECAST 
PERIOD. ENSEMBLE MODELS SHOW A VAST AMOUNT OF MEMBER DISPERSION, 
BASICALLY COVERING THE ENTIRETY OF THE NORTHWEST PACIFIC BASIN, MAKING 
THIS FORECAST EXTREMELY UNCERTAIN. THE JTWC FORECAST IS PLACED NEAR 
THE AI CONSENSUS MEAN, WITH VERY LOW CONFIDENCE. INTENSITY GUIDANCE IS 
GENERALLY IN AGREEMENT ON THE OVERALL INTENSITY TREND, BUT DIFFERS 
SIGNIFICANTLY IN THE PEAK INTENSITY. THE HAFS-A IS THE MOST AGGRESSIVE 
MODEL, PEAKING THE SYSTEM AT 85 KNOTS AT TAU 72, WHILE THE COTC MODEL 
IS THE LEAST AGGRESSIVE, REACHING A MAXIMUM OF 45 KNOTS. THE JTWC
FORECAST IS PLACED NEAR THE CONSENSUS MEAN, BUT AGAIN WITH VERY LOW
CONFIDENCE IN LIGHT OF THE ALTERNATE SCENARIO OUTLINED ABOVE.  

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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