026 WTNT34 KNHC 122050 TCPAT4 BULLETIN Tropical Storm Isaac Advisory Number 21 NWS National Hurricane Center Miami FL AL092018 500 PM AST Wed Sep 12 2018 ...ISAAC EXPECTED TO BRING TROPICAL STORM CONDITIONS TO PORTIONS OF THE LESSER ANTILLES... SUMMARY OF 500 PM AST...2100 UTC...INFORMATION ---------------------------------------------- LOCATION...15.4N 56.6W ABOUT 295 MI...480 KM E OF MARTINIQUE ABOUT 325 MI...525 KM E OF GUADELOUPE MAXIMUM SUSTAINED WINDS...60 MPH...95 KM/H PRESENT MOVEMENT...W OR 275 DEGREES AT 20 MPH...31 KM/H MINIMUM CENTRAL PRESSURE...1003 MB...29.62 INCHES WATCHES AND WARNINGS -------------------- CHANGES WITH THIS ADVISORY: None. SUMMARY OF WATCHES AND WARNINGS IN EFFECT: A Tropical Storm Warning is in effect for... * Martinique * Dominica * Guadeloupe A Tropical Storm Watch is in effect for... * Antigua * Montserrat * St. Kitts and Nevis * Saba and St. Eustatius * St. Martin and St. Maarten A Tropical Storm Warning means that tropical storm conditions are expected somewhere within the warning area, in this case within 24 hours. A Tropical Storm Watch means that tropical storm conditions are possible within the watch area, in this case within 24 hours. Interests elsewhere in the Leeward Islands should monitor the progress of Isaac. For storm information specific to your area, please monitor products issued by your national meteorological service. DISCUSSION AND OUTLOOK ---------------------- At 500 PM AST (2100 UTC), the center of Tropical Storm Isaac was located near latitude 15.4 North, longitude 56.6 West. Isaac is moving toward the west near 20 mph (31 km/h), and this general motion with a decrease in forward is expected to continue through the weekend. On the forecast track, Isaac is forecast to move across the central Lesser Antilles and into the eastern Caribbean Sea on Thursday, and then move across the eastern and central Caribbean Sea through Saturday. Maximum sustained winds remain near 60 mph (95 km/h) with higher gusts. Some weakening is forecast during the next 48 hours. Tropical-storm-force winds extend outward up to 175 miles (280 km) from the center. The estimated minimum central pressure is 1003 mb (29.62 inches). HAZARDS AFFECTING LAND ---------------------- RAINFALL: Isaac is expected to produce total rainfall accumulations of 2 to 4 inches with isolated amounts up to 8 inches across Martinique, Dominica, and Guadeloupe. Rainfall of 1 to 2 inches with isolated amounts to 4 inches are forecast across Puerto Rico and the southern United States Virgin Islands, with up to an inch anticipated across the remaining Windward and Leeward Islands. This rainfall may cause life-threatening flash flooding. WIND: Tropical storm conditions are expected on Martinique, Dominica, and Guadeloupe early Thursday. Tropical storm conditions are possible within the tropical storm watch area on Thursday. STORM SURGE: Some coastal flooding is possible in areas of onshore winds. Near the coast, the surge will be accompanied by large waves. SURF: Swells generated by Isaac are affecting portions of the Lesser Antilles. These swells are likely to cause life-threatening surf and rip current conditions. Please consult products from your local weather office. NEXT ADVISORY ------------- Next intermediate advisory at 800 PM AST. Next complete advisory at 1100 PM AST. $$ Forecaster Blake