000 WTPZ45 KNHC 100240 TCDEP5 HURRICANE LINDA DISCUSSION NUMBER 12 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL EP152009 800 PM PDT WED SEP 09 2009 LINDA HAS BECOME BETTER ORGANIZED DURING THE EVENING. AN EYE HAS BECOME APPARENT IN CONVENTIONAL SATELLITE IMAGERY...AND AN AMSU OVERPASS AT 0030 UTC SHOWED A BETTER DEFINED EYEWALL THAN A FEW HOURS AGO. SATELLITE INTENSITY ESTIMATES ARE 77 KT FROM TAFB AND 65 KT FROM SAB...AND THERE HAVE BEEN SEVERAL AMSU ESTIMATES OF 65 KT OR GREATER. BASED ON THIS...LINDA IS UPGRADED TO A HURRICANE WITH 70 KT WINDS. THE INITIAL MOTION IS 320/5. LINDA IS SOUTH OF A LOW-LEVEL RIDGE... WITH WATER VAPOR IMAGERY SHOWING A MID/UPPER-LEVEL TROUGH WEST OF THE HURRICANE AND A MID/UPPER-LEVEL RIDGE EAST OF IT. THE MID/UPPER-LEVEL FEATURES ARE TRYING TO STEER THE CYCLONE NORTHWARD...WHILE THE LOW-LEVEL RIDGE IS TRYING TO STEER IT MORE WESTWARD. THIS IS RESULTING IN A SLOW NORTHWESTWARD MOTION... WHICH SHOULD CONTINUE AS LONG AS LINDA KEEPS ITS VERTICALLY DEEP STRUCTURE. THE LARGE-SCALE GUIDANCE SUGGESTS THIS WILL BE FOR ABOUT 48-72 HR...AND THE NEW FORECAST TRACK IS AN UPDATE OF THE PREVIOUS TRACK THROUGH THAT TIME. AFTER THAT TIME...THE ECMWF...GFDN... NOGAPS...AND UKMET SHOW THE LOW-LEVEL CENTER OF LINDA TURNING MORE WESTWARD...WHILE THE GFS...HWRF...AND GFDL SHOW A GENERALLY NORTHWARD MOTION. THIS SPREAD SUGGESTS THAT THE MOTION SHOULD BE SLOW...AND THE NEW FORECAST TRACK COMPROMISES BETWEEN THESE EXTREMES BY SHOWING A SLOW NORTHWARD MOTION. ANALYSES FROM CIMSS AT THE UNIVERSITY OF WISCONSIN SHOW 20 KT OF SOUTHERLY VERTICAL WIND SHEAR OVER LINDA...AND SIMILAR SHEAR IS EXPECTED THROUGH THE REST OF THE FORECAST PERIOD. IN ADDITION... THE CYCLONE IS MOVING OVER SEA SURFACE TEMPERATURES OF 27C AND COLDER. THESE FACTORS SUGGEST THE CURRENT INTENSIFICATION SHOULD END SOON...AND THAT LINDA SHOULD STEADILY WEAKEN AFTER 12-24 HR. THE NEW INTENSITY FORECAST IS AN UPDATE OF THE PREVIOUS ADVISORY... AND CALLS FOR LINDA TO WEAKEN TO A TROPICAL STORM IN ABOUT 24 HR...A TROPICAL DEPRESSION IN ABOUT 72 HR...AND A REMNANT LOW IN ABOUT 96 HR. THE SHEAR IS FORECAST TO BE STRONG ON THE FORECAST TRACKS OF THE ECMWF AND THE OTHER WESTWARD-MOTION MODELS...SO EVEN IF LINDA AVOIDS THE COLD WATERS NORTH OF 20N IT IS STILL LIKELY TO WEAKEN TO A REMNANT LOW BEFORE 120 HR. FORECAST POSITIONS AND MAX WINDS INITIAL 10/0300Z 17.1N 129.4W 70 KT 12HR VT 10/1200Z 18.1N 130.1W 70 KT 24HR VT 11/0000Z 19.3N 131.0W 65 KT 36HR VT 11/1200Z 20.2N 131.7W 55 KT 48HR VT 12/0000Z 21.2N 132.5W 45 KT 72HR VT 13/0000Z 22.5N 133.5W 30 KT 96HR VT 14/0000Z 23.5N 133.5W 20 KT...REMNANT LOW 120HR VT 15/0000Z 24.0N 133.5W 20 KT...REMNANT LOW $$ FORECASTER BEVEN