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| #9456 (Received by flhurricane at: 5:15 PM 21.Sep.2004) TCDAT3 TROPICAL STORM LISA DISCUSSION NUMBER 10 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL 5 PM EDT TUE SEP 21 2004 LISA REMAINS A VERY COMPACT TROPICAL CYCLONE AND...AS SUCH...IS SUBJECT TO RAPID FLUCTUATIONS IN INTENSITY. THIS MAY HAVE BEEN THE CASE EARLIER TODAY AS AN SSMI OVERPASS INDCIATED THE MID-LEVEL CIRCULATION/EYE FEATURE BECAME DISPLACED A LITTLE TO THE SOUTHWEST OF THE LOW-LEVEL CENTER. THIS HAS RESULTED IN SIGNIFICANT DIFFERENCES IN THE SATELLITE POSITION ESTIMATES. THE INITIAL POSITION IS BETWEEN THE TWO CIRCULATION CENTERS. HOWEVER...DURING THE PAST FEW HOURS A BURST OF DEEP CONVECTION...TOPS COLDER THAN -80C...HAS DEVELOPED INTO A CDO-LIKE FEATURE OVER THE OLDER LOW-LEVEL CENTER LOCATED FARTHER TO THE EAST. THE INTENSITY REMAINS UNCHANGED AT 60 KT...WHICH IS ONLY SLIGHTLY HIGHER THAN THE DVORAK INTENSITY ESTIMATE OF T3.5...OR 55 KT...FROM TAFB. THE INITIAL MOTION ESTIMATE IS NOW 285/07. ONCE AGAIN...THERE REMAINS NO SIGNIFICANT CHANGE TO THE PREVIOUS FORECAST TRACK OR REASONING. MOST OF THE GLOBAL MODELS EITHER LOSE LISA WITHIN 24 HOURS...OR QUICKLY TURN THE CYCLONE NORTHWEST AND THEN NORTHWARD LIKE THE NOGAPS AND UKMET MODELS ARE INDICATING. HOWEVER...THOSE TWO MODELS HAVE HAD A PERSISTENT RIGHT-OF-TRACK BIAS THE PAST 24 HOURS SINCE THEY HAVE NOT HANDLED THE RIDGE BETWEEN KARL AND LISA VERY WELL. WHILE THE AFOREMENTIONED RIDGE IS NARROW...IT IS STRONG TO KEEP VERY SMALL LISA MOVING WEST TO WEST-NORTHWESTWARD. IN ADDITION...A LARGE TROPICAL DISTURBANCE LOCATED A FEW HUNDRED MILES SOUTHEAST OF LISA IS EXPECTED TO INDUCE SOME SOUTHWARD COMPONENT OF MOTION AS THAT DISTURBANCE CONTINUES TO LIKELY GROW AND INTENSITY. THE GFDL HAS BEEN THE ONLY MODEL TO CONSISTENTLY PICK UP ON THIS INTERACTION AND IT FORCES LISA SHARPLY SOUTHWARD IN 48 HOURS. WHILE THE SPECIFICS OF THE GFDL TRACK ARE LIKELY OVERDONE...ITS CONSISTENT TREND IN MOVING LISA SOUTHWARD CAN NOT BE IGNORED. A SLIGHT SOUTHWARD BEND IN THE TRACK IS INDICATED BY THE OFFICIAL FORECAST. THIS IS ALSO CONSISTENT WITH ALL THE GLOBAL MODELS FORECASTING A RIDGE TO BUILD OVER AND TO THE EAST OF THE LEEWARD ISLANDS BY 96-120 HOURS. DUE TO THE VERY SMALL SIZE OF LISA...NO SIGNIFICANT INTENSITY INCREASES ARE FORECAST...EVEN THOUGH RAPID FLUCTUATIONS ARE CERTAINLY POSSIBLE. FORECASTER STEWART FORECAST POSITIONS AND MAX WINDS INITIAL 21/2100Z 14.4N 40.3W 60 KT 12HR VT 22/0600Z 14.8N 41.5W 60 KT 24HR VT 22/1800Z 15.2N 43.0W 60 KT 36HR VT 23/0600Z 15.2N 44.5W 65 KT 48HR VT 23/1800Z 15.0N 45.7W 65 KT 72HR VT 24/1800Z 15.0N 47.0W 70 KT 96HR VT 25/1800Z 15.5N 48.5W 75 KT 120HR VT 26/1800Z 17.5N 50.5W 75 KT |
