MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 11W (KROSA) WARNING NR 007// RMKS// 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. TROPICAL STORM 11W (KROSA), LOCATED APPROXIMATELY 216 NM SOUTH OF IWO TO, HAS TRACKED NORTH-NORTHWESTWARD AT 08 KNOTS OVER THE PAST SIX HOURS. THE CURRENT POSITION IS BASED ON RECENT SATELLITE FIXES FROM PGTW AND RJTD AND 070336Z GMI 37 GHZ IMAGERY SHOWING A CLEAR CENTER FEATURE. THE INITIAL INTENSITY IS SET AT 60 KNOTS BASED ON A CONSENSUS OF SUBJECTIVE DVORAK AND AUTOMATED INTENSITY ESTIMATES FROM MULTIPLE SOURCES. TS 11W HAS CONTINUED TO STEADILY INTENSIFY OVER THE PAST SIX HOURS DUE TO PASSAGE OVER VERY WARM WATER (29-30C), AN IMPROVING POLEWARD AND EASTWARD OUTFLOW PATTERN ALOFT AND LIGHT TO MODERATE (15-20 KNOTS) VERTICAL WIND SHEAR. RECENT MICROWAVE SATELLITE IMAGERY, INCLUDING THE AFOREMENTIONED GMI PASS, INDICATE A CONTRACTING LOW LEVEL CIRCULATION CENTER, CONSISTENT WITH THE RECENT INTENSIFICATION TREND. TS 11W IS TRACKING NORTH-NORTHWESTWARD ALONG THE PERIPHERY OF SUBTROPICAL RIDGING SITUATED TO THE NORTH AND EAST. 3. FORECAST REASONING. A. THE EXTENDED FORECAST TRACK HAS SHIFTED A BIT WESTWARD RELATIVE TO THE PREVIOUS FORECAST IN ANTICIPATION OF A STEERING RIDGE BUILDING TO THE NORTH OF THE SYSTEM AFTER TAU 72. B. TS 11W IS EXPECTED TO CURVE FROM A NORTHWESTWARD ORIENTED TRACK TOWARD A NORTHEASTWARD ORIENTED TRACK OVER THE NEXT 72 HOURS AS RIDGING BUILDING TO THE SOUTH OF THE SYSTEM EXERTS AN INCREASING INFLUENCE ON STORM MOTION. FORWARD TRACK SPEED WILL REMAIN FAIRLY SLOW THROUGH AT LEAST TAU 48 AS RIDGE PATTERN REORIENTS AND THE ASSOCIATED STEERING INFLUENCES SHIFT. PASSAGE OVER WARM WATER AND THE FAVORABLE OUTFLOW PATTERN WILL RESULT IN FURTHER INTENSIFICATION OVER THE NEXT 48 HOURS OR SO. THEREAFTER, A SLIGHT INCREASE IN VERTICAL WIND SHEAR AND INTERACTION WITH A MORE STABLE AIR MASS TO THE NORTH ARE EXPECTED TO HINDER ADDITIONAL INTENSIFICATION. ALTHOUGH THERE ARE SUBTLE DIFFERENCES IN THE ORIENTATION OF THE STEERING RIDGES DURING THIS PERIOD, NUMERICAL MODEL GUIDANCE IS IN GOOD OVERALL AGREEMENT REGARDING THE TRACK SCENARIO. THE CURRENT TRACK FORECAST IS PLACED NEAR THE MULTI-MODEL CONSENSUS AND PREVIOUS JTWC TRACK FORECASTS THROUGH TAU 72, WITH HIGH CONFIDENCE. C. MODEL GUIDANCE DIVERGES IN THE EXTENDED FORECAST PERIOD, WITH A GROUPING CONSISTING OF THE GFS, NAVGEM AND JGSM MODELS DEPICTING A NORTH-NORTHWESTWARD TO POLEWARD TRACK AND A SECOND GROUPING CONSISTING OF THE ECMWF, ECMWF ENSEMBLE AND UKMET MODEL DEPICTING A STEADY NORTHWESTWARD TRACK. IN BOTH MODEL SCENARIOS, RIDGING TO THE NORTH OF THE SYSTEM WEAKENS IN THE NEAR TERM IN RESPONSE TO A DEVELOPING MIDLATITUDE TROUGH. THE ECMWF AND UKMET MODELS INDICATE THAT A RIDGE WILL BUILD TO THE NORTH OF TS 11W, IN THE WAKE OF THIS TROUGH, AND TAKE OVER AS THE DOMINANT STEERING MECHANISM. THIS RIDGE WILL SENDING THE SYSTEM ON A TRAJECTORY TO THE WEST OF THE OTHER MODEL GROUP. THIS SCENARIO APPEARS INCREASINGLY PROBABLE GIVEN AN ANTICIPATED ZONAL MIDLATITUDE FLOW PATTERN. THUS THE CURRENT JTWC TRACK FORECAST LIES TO THE LEFT OF THE MULTI-MODEL CONSENSUS IN FAVOR OF THE ECMWF, UKMET GROUPING. ADDITIONAL ADJUSTMENTS MAY BE NECESSARY IN SUBSEQUENT FORECASTS. GIVEN THE NOTED BIFURCATION IN THE MODEL GUIDANCE, CONFIDENCE IN THE JTWC TRACK FORECAST IS LOW FOR THE EXTENDED PERIOD. RESTRICTED OUTFLOW AND ENTRAINMENT OF MORE STABLE AIR ARE EXPECTED TO REDUCE INTENSITY A BIT IN THE EXTENDED RANGE.// NNNN NNNN