WDPN35 PGTW 241500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 15W (FIFTEEN) 
WARNING NR 11//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TROPICAL DEPRESSION (TD) 15W (FIFTEEN), LOCATED APPROXIMATELY 376 
NM SOUTHWEST OF IWO TO, JAPAN, HAS TRACKED NORTHWARD AT 09 KNOTS OVER
THE PAST SIX HOURS. ANIMATED ENHANCED INFRARED SATELLITE IMAGERY 
DEPICTS A CONSOLIDATING SYSTEM WITH A COMPACT, APPROXIMATELY 130NM 
DIAMETER, CORE OF DEEP CONVECTION PERSISTING OVER THE LOW-LEVEL 
CIRCULATION CENTER (LLCC). A 241228Z METOP-B 89GHZ IMAGE SHOWS A 
CURVED CONVECTIVE BAND OVER THE NORTH AND WEST QUADRANTS WITH A 
WEAKLY-DEFINED LLCC POSITIONED ON THE EASTERN EDGE OF THIS BAND, 
WHICH PROVIDES MODERATE CONFIDENCE IN THE INITIAL POSITION. THE 
INITIAL INTENSITY IS ASSESSED AT 30 KNOTS BASED ON DVORAK ESTIMATES 
RANGING FROM T1.5 (25 KNOTS) TO T2.5 (35 KNOTS). HOWEVER, RECENT 
ASCAT DATA SUGGESTS SOME ISOLATED 35 KNOT WINDS, WHICH SHOULD 
SUPPORT THE UPGRADE TO TROPICAL STORM STRENGTH ON THE 24/18Z 
WARNING. UPPER-LEVEL ANALYSIS INDICATES A MARGINALLY FAVORABLE 
ENVIRONMENT WITH WEAK POLEWARD OUTFLOW INTO A NARROW TUTT POSITIONED 
TO THE NORTH AND LOW VERTICAL WIND SHEAR. TD 15W IS TRACKING SLOWLY 
NORTHWARD TO NORTH-NORTHEASTWARD ALONG THE NORTHWESTERN PERIPHERY OF 
THE NEAR-EQUATORIAL RIDGE (NER) POSITIONED TO THE SOUTHEAST. 
3. FORECAST REASONING.
   A. THERE IS NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE 
PREVIOUS PROGNOSTIC REASONING MESSAGE.
   B. TD 15W IS LOCATED WITHIN A COMPETING STEERING ENVIRONMENT 
BETWEEN THE SUBTROPICAL RIDGE (STR) TO THE NORTH AND THE 
AFOREMENTIONED NER, THEREFORE, THE SYSTEM WILL CONTINUE TO TRACK 
SLOWLY NORTH-NORTHEASTWARD THROUGH TAU 24. DUE TO THE MARGINALLY-
FAVORABLE ENVIRONMENT, SPECIFICALLY THE LACK OF STRONG POLEWARD 
OUTFLOW, TD 15W IS EXPECTED TO INTENSIFY SLOWLY TO ABOUT 50 KNOTS BY 
TAU 36. AFTER TAU 36, TD 15W WILL ACCELERATE NORTHEASTWARD TO NORTH-
NORTHEASTWARD AS THE STEERING RIDGE TO THE EAST STRENGTHENS AND THE 
STR TO THE NORTH WEAKENS AND RECEDES WESTWARD. AFTER TAU 36, THE 
SYSTEM IS FORECAST TO INTENSIFY AT A GREATER RATE AS A STRONG UPPER 
LOW DEEPENS SOUTHEAST OF HONSHU ENHANCING POLEWARD OUTFLOW. 
CONSEQUENTLY, THE SYSTEM WILL PEAK AT 90 KNOTS BY TAU 72. NUMERICAL 
MODEL GUIDANCE REMAINS IN POOR AGREEMENT WITH A LARGE SPREAD IN 
SOLUTIONS AT TAU 72 DUE TO MAJOR DIFFERENCES IN TRACK SPEEDS AND THE 
GENERAL TRACK ORIENTATION. NAVGEM AND COAMPS-TC HAVE COME INTO 
BETTER AGREEMENT WITH THE BULK OF THE GUIDANCE, HOWEVER, GFS AND 
HWRF REMAIN EASTERN OUTLIERS AND SHOW A SLOW BUT PLAUSIBLE 
NORTHEASTWARD TRACK. THE REMAINDER OF THE GUIDANCE SHOWS FASTER 
TRACK SPEEDS AND A TRACK OVER IWO TO. DUE TO THE LARGE DEGREE OF 
UNCERTAINTY IN THIS PORTION OF THE FORECAST TRACK, THERE IS LOW 
CONFIDENCE IN THE JTWC FORECAST TRACK.
   C. AFTER TAU 72, NUMERICAL MODEL GUIDANCE REMAINS IN POOR 
AGREEMENT WITH INCREASING UNCERTAINTY DUE TO A COMPLEX, EVOLVING 
STEERING ENVIRONMENT. TD 15W IS FORECAST TO TRACK AROUND THE EASTERN 
AND EVENTUALLY NORTHERN PERIPHERY OF THE AFOREMENTIONED BROAD LOW 
POSITIONED SOUTHEAST OF HONSHU. THE PRIMARY STEERING INFLUENCE 
DURING THIS PHASE TRANSITIONS FROM THE NER TO A STRONG STR 
POSITIONED NORTHEAST OF THE UPPER LOW. TO RE-EMPHASIZE, THERE IS A 
SIGNIFICANT DEGREE OF UNCERTAINTY IN THE EXACT TRAJECTORY AND TIMING 
OF THIS NORTHWESTWARD TRACK CHANGE TOWARD AND OVER HONSHU. THE JTWC 
FORECAST FAVORS THE JGSM, ECMWF SOLUTIONS AS THE MOST REALISTIC, 
VIABLE SOLUTIONS AND IS POSITIONED NEAR THE MULTI-MODEL CONSENSUS. 
TD 15W IS FORECAST TO WEAKEN GRADUALLY DURING THE EXTENDED PERIOD 
DUE TO INTERACTION WITH THE UPPER LOW AND INTERACTION WITH LAND.//
NNNN