000 WTPZ45 KNHC 191432 TCDEP5 HURRICANE RICK DISCUSSION NUMBER 17 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL EP202009 800 AM PDT MON OCT 19 2009 SOUTHWESTERLY SHEAR...ANALYZED AT 15 TO 20 KNOTS BY THE SHIPS MODEL AND UW-CIMSS...APPEARS TO BE TAKING A TOLL ON RICK. THE CLOUD PATTERN HAS CONTINUED TO DETERIORATE...WITH AN EROSION OF THE COLD CLOUD TOPS IN THE WESTERN SEMICIRCLE AND THE DISAPPEARANCE OF THE EYE IN GEOSTATIONARY IMAGERY. AN AMSR-E PASS FROM 0913 UTC SHOWED THAT THE SOUTHWESTERN EYEWALL HAS ERODED AND ALSO SUGGESTS THAT THE CIRCULATION MAY BE BECOMING VERTICALLY TILTED. SATELLITE INTENSITY ESTIMATES HAVE DECREASED...AND THE INITIAL INTENSITY OF 100 KT IS BASED ON A BLEND OF DVORAK DATA-T NUMBERS AND CI-NUMBERS FROM TAFB...SAB...AND THE UW-CIMSS ADT. AN AIR FORCE RESERVE RECONNAISSANCE AIRCRAFT IS CURRENTLY EN ROUTE TO INVESTIGATE RICK AND WILL PROVIDE VALUABLE DATA TO HELP DETERMINE THE INTENSITY AND STRUCTURE OF THE HURRICANE LATER TODAY. THE SHIPS MODEL SUGGESTS THAT RICK WILL BE EXPERIENCING VERTICAL SHEAR OF 15 TO 20 KNOTS FOR MOST OF THE FORECAST PERIOD...EXCEPT FOR A BRIEF REDUCTION BETWEEN 12 AND 24 HOURS. GIVEN THIS...ALONG WITH CURRENT SATELLITE TRENDS...THE INTENSITY FORECAST HAS BEEN ADJUSTED DOWNWARD...BUT REMAINS ABOVE THE ICON INTENSITY CONSENSUS THROUGH 24 HOURS OUT OF RESPECT FOR CONTINUITY. BEYOND 24 HOURS THE OFFICIAL FORECAST IS CLOSE TO ICON AND SHOWS RICK WEAKENING TO A TROPICAL STORM IN 72 HOURS AFTER MAKING LANDFALL IN MAINLAND MEXICO. THE INITIAL MOTION ESTIMATE IS 305/08...A LITTLE TO THE LEFT OF THE PREVIOUS PACKAGE BASED ON GEOSTATIONARY AND MICROWAVE IMAGERY. RICK SEEMS TO BE SLOWING DOWN AS THE SUBTROPICAL RIDGE NORTH OF THE HURRICANE WEAKENS DUE TO A PAIR OF SHORTWAVE TROUGHS DIGGING INTO THE SOUTHWESTERN UNITED STATES OVER THE NEXT COUPLE OF DAYS. MOST OF THE TRACK GUIDANCE REMAINS TIGHTLY CLUSTERED AROUND A SCENARIO THAT SHOWS RICK ACCELERATING TOWARD THE NORTH AND NORTHEAST AS IT INTERACTS WITH THE AFOREMENTIONED TROUGHS. AN ALTERNATIVE SCENARIO ...WHERE THE CIRCULATION OF RICK BECOMES VERTICALLY DECOUPLED LEAVING THE LOW-LEVEL CENTER BEHIND...IS REPRESENTED BY THE UKMET MODEL AND THE SHALLOW BAM. THE OFFICIAL FORECAST FOLLOWS THE FIRST SCENARIO...AND IS ADJUSTED SLIGHTLY TO THE RIGHT OF THE PREVIOUS FORECAST BEYOND 12 HOURS TOWARD THE MODEL CONSENSUS. IN THE FIRST 12 HOURS...THE FORECAST IS SLIGHTLY LEFT OF THE PREVIOUS PACKAGE DUE TO THE INITIAL POSITION AND MOTION. THE INITIAL WIND RADII WERE ADJUSTED BASED ON INFORMATION FROM AN ASCAT PASS AT AROUND 0500 UTC. FORECAST POSITIONS AND MAX WINDS INITIAL 19/1500Z 17.8N 111.6W 100 KT 12HR VT 20/0000Z 18.6N 112.2W 90 KT 24HR VT 20/1200Z 19.7N 111.9W 80 KT 36HR VT 21/0000Z 21.1N 111.0W 75 KT 48HR VT 21/1200Z 22.8N 109.6W 70 KT 72HR VT 22/1200Z 25.5N 106.5W 35 KT...INLAND 96HR VT 23/1200Z...DISSIPATED $$ FORECASTER BRENNAN