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| #9044 (Received by flhurricane at: 4:56 PM 17.Sep.2004) TCDAT1 TROPICAL DEPRESSION JEANNE DISCUSSION NUMBER 17 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL 5 PM EDT FRI SEP 17 2004 A USAF RESERVE UNIT AIRCRAFT LOCATED THE CENTER JUST OFFSHORE FROM HISPANIOLA WITH 1002 MB CENTRAL PRESSURE AND MAXIMUM 700-MB FLIGHT LEVEL WINDS OF ONLY 34 KT NORTHEAST AND NORTHWEST OF THE CENTER. JEANNES INTERACTION WITH LAND HAS TAKEN ITS TOLL AND THE STORM IS DOWNGRADED TO A TROPICAL DEPRESSION BASED ON THIS DATA. THE INITIAL MOTION ESTIMATE IS 295/08. THE TRACK FORECAST SCENARIO REMAINS THE SAME FOR THE FIRST 3 DAYS WITH A NORTHWEST TO NORTHWARD MOTION INTO A WEAKNESS DEVELOPING IN THE MID-LEVEL RIDGE TO THE NORTH OF JEANNE. THE GFS AND GFDL EVEN SHOW SOME EASTWARD COMPONENT OF MOTION AFTER 2 DAYS. THEREAFTER THERE IS AN EASTWARD SHIFT TO ALL OF THE GUIDANCE. THE UKMET AND NOGAPS SHOW A SLOW WESTWARD DRIFT FOR 4 AND 5 DAYS WHILE THE GFDL AND GFS SHOW A NORTHEAST OR EASTWARD MOTION. EXACTLY WHAT HAPPENS IS DEPENDENT ON THE EVOLUTION OF THE REMAINS OF IVAN AND THERE IS DISAGREEMENT ON THIS. THE OFFICIAL FORECAST MOVES JEANNE NORTHWEST TO NORTHWARD FOR 3 DAYS AND THEN HOLDS THE MOTION STATIONARY SEVERAL HUNDRED MILES NORTHEAST OF THE NORTHERN BAHAMAS. THIS IS A SIGNIFICANT EASTWARD SHIFT FROM THE PREVIOUS ADVISORY AND IMPLIES A REDUCED RISK TO THE SOUTHEASTERN U.S. DURING THE NEXT 5 DAYS...ALTHOUGH THE MODEL SPREAD INDICATES INCREASED UNCERTAINTY ASSOCIATED WITH THIS PARTICULAR FORECAST. SOME OF THE CURRENT WEAKENING MAY ALSO BE DUE TO 18 KT OF VERTICAL SHEAR AS DIAGNOSED BY THE SHIPS MODEL. DECREASING SHEAR IS FORECAST THROUGH 36 HOURS AND MOST GUIDANCE CALLS FOR MODEST STRENGTHENING. THE OFFICIAL FORECAST IS TO 55 KT IN 48 HOURS COMPARED TO THE PREVIOUS ADVISORY WHICH CALLED FOR A HURRICANE IN 36 HOURS BUT WHICH STARTED WITH A WIND SPEED THAT WAS 25 KT TOO HIGH. FORECASTER LAWRENCE FORECAST POSITIONS AND MAX WINDS INITIAL 17/2100Z 20.2N 71.8W 30 KT 12HR VT 18/0600Z 21.0N 73.0W 35 KT 24HR VT 18/1800Z 22.0N 74.0W 45 KT 36HR VT 19/0600Z 23.7N 74.7W 50 KT 48HR VT 19/1800Z 25.8N 74.7W 55 KT 72HR VT 20/1800Z 29.0N 75.0W 55 KT 96HR VT 21/1800Z 29.0N 75.0W 55 KT 120HR VT 22/1800Z 29.0N 75.0W 50 KT |
