36 Continued from previous page Hurricane Watch: An announcement for specific coastal areas that hurricane conditions are possible within 36 hours. Indirect Hit: Generally refers to locations that do not experience a direct hit from a tropical cyclone, but do experience hurricane force winds (either sustained or gusts) or tides of at least four feet above normal. Landfall: The intersection of the surface centre of a tropical cyclone with a coastline. Because the strongest winds in a tropical cyclone are not located precisely at the centre, it is possible for a cyclone's strongest winds to be experienced over land even if landfall does not occur. Major Hurricane: A hurricane that is classified as Category 3 or higher. Storm Surge: An abnormal rise in sea level accompanying a hurricane or other intense storm, and whose height is the difference between the observed level of the sea surface and the level that would have occurred in the absence of the cyclone. Storm surge is usually estimated by subtracting the normal or astronomic high tide from the observed storm tide. Storm Warning: A warning of 1-minute sustained surface winds of 48 knots t (55 mph or 88 km/hr) or greater, predicted or occurring, not directly associated with tropical cyclones. Tropical Depression: A tropical cyclone in which the maximum sustained surface wind speed (using the U.S. 1-minute average) is 33 knots (38 mph or 62 km/hr) or less. Tropical Disturbance: A discrete tropical weather system of apparently organised convection — generally 100 to 300 nautical miles in diameter — originating in the tropics or subtropics, having a non-frontal migratory character, and maintaining its identity for 24 hours or more. It may or may not be associated with a detectable perturbation of the wind field. Tropical Storm: A tropical cyclone in which the maximum sustained surface wind speed (using the U.S. 1-minute average) ranges from 34 knots (39 mph or 63 km/ hr) to 63 knots (73 mph or 118 km/hr). Tropical Storm Warning: A warning that sustained winds within the range of 34 to 63 knots (39 to 73 mph or 63 to 118 km/hr) associated with a tropical cyclone are expected in a specified coastal area within 24 hours or less. Tropical Storm Watch: An announcement for specific coastal areas that tropical storm conditions are possible within 36 hours. Tropical Wave: A trough or cyclonic curvature maximum in the trade-wind easterlies. The wave may reach maximum amplitude in the lower middle troposphere.
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