WDPN32 PGTW 300900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 23W (ATSANI) 
WARNING NR 004//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TROPICAL DEPRESSION 23W (ATSANI), LOCATED APPROXIMATELY 147 NM 
SOUTH-SOUTHWEST OF ANDERSEN AFB, GUAM HAS TRACKED NORTHWESTWARD AT 
26 KNOTS OVER THE PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE 
IMAGERY (MSI) DEPICTS A VERY DISORGANIZED SYSTEM WITH FLARING 
CONVECTION WRAPPING INTO A BROAD AREA OF WEAK TURNING, WITH NO 
DISTINCT LOW LEVEL CIRCULATION CENTER (LLCC) EVIDENT IN AVAILABLE 
IMAGERY. THERE HAVE BEEN NO MICROWAVE OR SCATTEROMETER PASSES SINCE 
THE 0000Z HOUR AND THERE ARE POSSIBLY MULTIPLE CIRCULATIONS EMBEDDED 
IN THE BROADER CIRCULATION. THE INITIAL POSITION IS PLACED WITH LOW 
CONFIDENCE BASED PRIMARILY ON SPIRAL BAND ANALYSIS OF THE FEW LOW-
LEVEL CLOUD BANDS EVIDENT IN ANIMATED MSI. THE INITIAL INTENSITY IS 
ASSESSED AT 30 KTS BASED ON SUBJECTIVE DVORAK ESTIMATES OF T2.0 (30 
KNOTS) FROM PGTW, AN ADVANCED DVORAK TECHNIQUE ESTIMATE OF 2.8 AND A 
SATELLITE CONSENSUS ESTIMATE OF 39 KNOTS; HOWEVER, THE AUTOMATED 
TECHNIQUES ARE ANALYZING A POSITION DISPLACED WELL TO THE SOUTHEAST 
OF THE ASSESSED LLCC, AND ARE UNREPRESENTATIVE. ENVIRONMENTAL 
ANALYSIS INDICATES THE SYSTEM LIES IN A REGION OF MODERATE TO STRONG 
(20-25 KNOT) VWS FROM THE OUTFLOW FROM STY 22W, OFFSETTING ROBUST 
EQUATORWARD OUTFLOW AND WARM (30 TO 31 DEGREE CELSIUS) SEA SURFACE 
TEMPERATURES. TD 23 IS CURRENTLY TRACKING RAPIDLY NORTHWESTWARD 
ALONG THE SOUTHWEST PERIPHERY OF A DEEP-LAYER SUBTROPICAL RIDGE 
(STR) CENTERED TO THE NORTHEAST.
3. FORECAST REASONING.
   A. NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS 
PROGNOSTIC REASONING MESSAGE.
   B. TD 23W IS FORECAST TO CONTINUE TRACKING NORTHWESTWARD, 
TRACKING ALONG THE SOUTHWESTERN EDGE OF THE STR TO THE NORTHEAST 
THROUGH TAU 72. THE SYSTEM WILL CONTINUE TO SLOWLY AND STEADILY 
INTENSIFY THROUGH TAU 48 IN SPITE OF MARGINAL ENVIRONMENTAL 
CONDITIONS, WITH THE CONVERGENT EQUATORWARD OUTFLOW FROM STY 22W 
LIMITING THE OUTFLOW AVAILABLE FOR TD 23W TO A SINGLE EQUATORWARD 
CHANNEL. THIS CONVERGENCE, COMBINED WITH MODERATE VWS (15-20 KTS), 
WILL SERVE TO OFFSET THE VERY WARM (30 DEG CELSIUS) WATERS. AFTER 
TAU 48 THE SYSTEM IS FORECAST TO MOVE UNDER A DEVELOPING UPPER-LEVEL 
ANTICYCLONE, WHICH WILL PROVIDE FOR MORE ROBUST RADIAL OUTFLOW AND 
RESULT IN A STEEPER RATE OF INTENSIFICATION THROUGH TAU 72. DYNAMIC 
MODEL GUIDANCE IS IN POOR AGREEMENT, WITH A DISTINCT BIFURCATION 
FROM TAU 12. THE NAVGEM MODEL IS CURRENTLY THE ONLY CONSENSUS MEMBER 
THE CONTINUES TO RECURVE THE SYSTEM NORTHEAST INTO THE WESTERLIES, 
WHILE GFS, ECMWF AND THEIR ENSEMBLES, AS WELL AS THE AFUM MODEL, ALL 
INDICATE A SLOWING OF THE FORWARD SPEED BEGINNING AT TAU 72, AND 
THEN A TURN WESTWARD, LEADING TO A CROSS-TRACK SPREAD OF 400 NM AT 
TAU 72. THE REMAINDER OF THE GUIDANCE PACKAGE LIES VERY CLOSE TO THE 
MULTI-MODEL CONSENSUS AVERAGE. THE JTWC FORECAST TRACK HAS BEEN 
PLACED ALONG THE SOUTHERN EDGE OF THE GUIDANCE ENVELOPE THROUGH TAU 
72, AS A NOD TOWARDS THE GFS AND ECMWF SOLUTIONS WITH LOW 
CONFIDENCE.  
   C. BEYOND TAU 72, THE SYSTEM WILL SLOW SIGNIFICANTLY AS IT MOVES 
INTO A WEAK STEERING ENVIRONMENT, DOMINATED BY A COL AREA WHICH 
DEVELOPS DUE TO A WEAKNESS IN THE STR INDUCED BY THE APPROACH OF 
DEEP MID-LATITUDE TROUGH TO THE NORTH. AS IT TRACKS NORTHWESTWARD IT 
BEGINS TO TAP INTO DUAL-CHANNEL OUTFLOW, ALLOWING IT TO INTENSIFY TO 
95 KNOTS AT TAU 120. THE STEERING MECHANISM SHIFTS BY TAU 96 TO THE 
STR TO THE WEST OVER CHINA LEADING TO A MORE WESTWARD TRACK THROUGH 
THE END OF THE FORECAST. NUMERICAL MODEL GUIDANCE IS HIGHLY 
DIVERGENT, WITH THE AFOREMENTIONED BIFURCATION BECOMING INCREASINGLY 
EVIDENT IN LONG RANGE FORECAST. THE CROSS-TRACK SPREAD BETWEEN THE 
NAVGEM AND GFS OUTLIERS INCREASES TO NEARLY 900 NM BY TAU 120 WITH 
THE REMAINDER OF THE CONSENSUS MEMBERS TIGHTLY PACKED AND FAIRLY 
EVENLY DISTRIBUTED IN ROUGHLY THE MIDDLE OF THE BIFURCATION 
ENVELOPE. THE JTWC TRACK IS PLACED ALONG THE SOUTHERN SIDE OF THE 
TIGHTEST MODEL PACKING, AS A HEDGE TOWARDS THE GFS AND ECMWF 
SOLUTIONS, WITH VERY LOW CONFIDENCE.//
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