WDPN32 PGTW 292100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 23W (ATSANI) WARNING NR 002//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TROPICAL DEPRESSION 23W (ATSANI), LOCATED APPROXIMATELY 297 NM SOUTH-SOUTHEAST OF ANDERSEN AFB, GUAM HAS TRACKED NORTH-NORTHWESTWARD AT 13 KNOTS OVER THE PAST SIX HOURS. ANIMATED ENHANCED INFRARED SATELLITE IMAGERY DEPICTS A BROAD AREA OF GENERALLY DISORGANIZED DEEP CONVECTIVE ACTIVITY. A 291610Z AMSR2 89 GHZ PASS SUGGESTS THE LOW LEVEL CIRCULATION CENTER (LLCC) MAY BE CONSOLIDATING AROUND A DEVELOPING VORTICAL TOWER NEAR THE CENTER OF THE CONVECTIVE MASS, WHILE ACTIVITY ALONG THE NORTHERN PERIPERY APPEARS LINEAR AND NOT WRAPPING. THE CIMSS 850 MB VORTICITY PRODUCT ALSO DEPICTS THE CURRENT STRUCTURE ASYMMETRY.THERE IS A HIGH DEGREE OF UNCERTAINTY IN THE INITIAL PLACEMENT AS THE LLCC IS NOT FIRMLY ESTABLISHED AND MAY SHIFT. THE INITIAL POSITION IS BASED ON FIXES FROM PGTW AND RJTD, AND THE AFOREMENTED AMSR2 DATA.  THE INITIAL INTENSITY IS ASSESSED AT 25 KTS BASED ON SUBJECTIVE DVORAK ESTIMATES. THE AMSR2 WINDSPEED PRODUCT INDICATES AN ISOLATED AREA OF 30 TO 34 KNOT WINDS TO THE EAST, HOWEVER, AN EARLIER SCAT PASS AND CURRENT STRUCTURE ANALYSIS INDICATES THESE ISOATED HIGHER WINDS ARE NOT REPRESENTATIVE OF THE SYSTEM?S OVERALL DEVELOPMENT AT THIS TIME. UPPER LEVEL ANALYSIS INDICATES MODERATE (15-20 KNOT) VERTICAL WIND SHEAR OVER THE SYSTEM MAY BE HAMPERING DEVELOPMENT, HOWEVER, THIS IS PARTIALLY OFFSET BY DIVERGENCE OVER THE LLCC. 30 TO 31 DEGREE CELSIUS SEA SURFACE TEMPERATURES ARE VERY FAVORABLE. TD 23 IS CURRENTLY TRACKING GENERALLY NORTHWESTWARD ALONG A RIDGE OF HIGH PRESSURE TO THE EAST.
3. FORECAST REASONING.
   A. NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS PROGNOSTIC REASONING MESSAGE.
   B. TD 23W IS FORECAST TO CONTINUE ITS PIVOT TO A MORE NORTHWESTWARD TRACK OVER THE NEXT 12 HOURS, AS THE STEERING RIDGE REORIENTS SLIGHTLY, AND IS FORECAST TO CONTINUE THIS NORTHWESTWARD TRACK THROUGH TAU 72. AS THE SYSTEM TRACKS NORTHWESTWARD, IT WILL BEGIN TO BE IMPACTED BY THE OUTFLOW FROM TY 22W, WITH CONVERGENT UPPER-LEVEL FLOW MOVING DOWN FROM THE NORTH LIMITING THE AVAILABLE OUTFLOW TO A SINGLE WESTWARD CHANNEL. THIS, COMBINED WITH MODERATE VWS WILL OFFSET THE VERY WARM (30 DEG CELSIUS) WATERS TO LIMIT THE SYSTEM?S INTENSIFICATION THROUGH TAU 48. AFTER TAU 48 THE UPPER-LEVEL PATTERN WILL BEGIN TO SHIFT AND PROVIDE INCREASING DIVERGENT OUTFLOW ALLOWING THE SYSTEM TO START INTENSIFYING AT A FASTER RATE, INCREASING TO 80 KNOTS BY TAU 72. THE JTWC FORECAST TRACK IS PLACED WITH HIGH CONFIDENCE THROUGH TAU 48 AND LIES SLIGHTLY SOUTH OF THE MULTI-MODEL CONSENSUS TO ACCOUNT FOR JGSM, WHICH IS FAR TO THE NORTH OF THE REMAINDER OF THE MODELS AT TAU 48. HOWEVER, NUMERICAL MODEL GUIDANCE DIVERGES MORE AFTER TAU 48 LEADING TO MODERATE CONFIDENCE BETWEEN TAUS 48-72 WITH CROSS-TRACK SPREAD INCREASING TO 250 NM AT TAU 72 WITH AFUM AND GFS REPRESENTING THE NORTH AND SOUTH OUTLIERS.  
   C. BEYOND TAU 72, THE SYSTEM WILL SLOW DOWN WHILE TURNING SLIGHTLY MORE NORTHWARD TOWARDS A WEAKNESS A COL AREA THAT DEVELOPS IN A WEAKNESS IN THE STR TO THE NORTH. AS THE SYSTEM CLOSER TO THE COL REGION, IT BEGINS TO TAP INTO DUAL-CHANNEL OUTFLOW, ALLOWING IT TO INTENSIFY TO 100 KNOTS AT TAU 120. NUMERICAL GUIDANCE IS MIXED BEYOND TAU 72, WITH A BIFURCATION SCENARIO SETTING UP AFTER TAU 96. THE GFS SOLUTION TRACKS TD 23W FURTHER TO THE SOUTH WHEREAS AFUM TURNS TO THE NORTH AFTER TAU 96, LEADING TO A VERY LARGE 630 NM SPREAD AT TAU 120. THE ECMWF FAVORS A SLOWER TRACK BEFORE TURNING DUE WEST AFTER TAU 120. THE JTWC FORECAST TRACKS SLOWER AND JUST WEST OF THE MULTI-MODEL CONSENSUS AND FAVORS THE ECMWF SOLUTION WITH LOW CONFIDENCE.//
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