000 WTNT43 KNHC 082041 TCDAT3 TROPICAL STORM CHANTAL DISCUSSION NUMBER 4 NWS NATIONAL HURRICANE CENTER MIAMI FL AL032013 500 PM AST MON JUL 08 2013 LITTLE CHANGE IN THE CONVECTIVE ORGANIZATION OF CHANTAL HAS OCCURRED TODAY...SO THE INTENSITY IS BEING MAINTAINED AT 40 KT. HOWEVER...AN AIR FORCE RESERVE RECONNAISSANCE AIRCRAFT IS ENROUTE TO THE CYCLONE AND IT WILL PROVIDE A BETTER ESTIMATE OF THE INTENSITY SHORTLY. VISIBLE AND WATER VAPOR IMAGERY CONTINUE TO INDICATE AN INCREASE IN THE UPPER-LEVEL ANTICYCLONIC OUTFLOW PATTERN. THE INITIAL MOTION ESTIMATE IS NOW 290/23 KT. CHANTAL IS FORECAST TO REMAIN SOUTH OF A STRONG DEEP-LAYER SUBTROPICAL RIDGE FOR THE NEXT 2 DAYS...SO A GENERAL WEST-NORTHWESTWARD MOTION IS EXPECTED DURING THAT TIME. BY DAYS 3-5...A LARGE MID-/UPPER-LEVEL LOW CURRENTLY MOVING WESTWARD THROUGH THE BAHAMAS IS FORECAST BY THE GLOBAL MODELS TO MOVE ACROSS FLORIDA AND PHASE UP WITH A MID-LATITUDE TROUGH...WHICH SHOULD CREATE A BREAK IN THE RIDGE AXIS AND PRODUCE A WEAKER STEERING PATTERN OVER THE SOUTHEASTERN U.S. AND THE BAHAMAS. AS A RESULT...CHANTAL IS EXPECTED TO SLOW DOWN AND TURN NORTHWESTWARD BY 72 HOURS AS IT APPROACHES THE WEAKNESS IN THE RIDGE...AND THEN MOVE SLOWLY NORTH-NORTHWESTWARD OR NORTHWARD ON DAYS 4 AND 5 AS THE STEERING FLOW COLLAPSES. THE OFFICIAL FORECAST TRACK HAS BEEN SHIFTED SLIGHTLY TO THE RIGHT OF THE PREVIOUS ADVISORY TRACK...BUT NOT NEARLY AS FAR RIGHT AS THE MODEL CONSENSUS. ENVIRONMENTAL CONDITIONS AROUND AND AHEAD OF CHANTAL FAVOR AT LEAST MODEST STRENGTHENING DURING THE NEXT 48 HOURS OR SO WHILE THE CYCLONE REMAINS UNDER THE INFLUENCE OF UPPER-LEVEL RIDGING...AND CHANTAL IS EXPECTED TO BE NEAR HURRICANE STRENGTH BEFORE IT REACHES HISPANIOLA. AFTER CHANTAL MOVES PAST HISPANIOLA ON DAY 2/3...THE CYCLONE SHOULD BE AFFECTED BY MODERATE TO STRONG WESTERLY VERTICAL WIND SHEAR ASSOCIATED WITH AN UPPER-LEVEL TROUGH ACROSS FLORIDA... WHICH IS EXPECTED TO FURTHER ENHANCE THE WEAKENING PROCESS. THE OFFICIAL INTENSITY FORECAST IS SIMILAR TO THE PREVIOUS ADVISORY AND ESSENTIALLY FOLLOWS THE ICON CONSENSUS MODEL. FORECAST POSITIONS AND MAX WINDS INIT 08/2100Z 11.8N 53.9W 40 KT 45 MPH 12H 09/0600Z 13.0N 57.3W 45 KT 50 MPH 24H 09/1800Z 14.6N 61.7W 50 KT 60 MPH 36H 10/0600Z 16.2N 66.0W 55 KT 65 MPH 48H 10/1800Z 17.8N 69.6W 60 KT 70 MPH 72H 11/1800Z 21.0N 74.5W 45 KT 50 MPH 96H 12/1800Z 24.3N 76.6W 30 KT 35 MPH 120H 13/1800Z 26.7N 78.0W 30 KT 35 MPH $$ FORECASTER STEWART