Wind speeds measured at high altitudes unaffected by local terrain conditions. Hurricane hunters, the planes flown over hurricanes to make measurements of wind speeds and pressures, measure the gradient wind speed. Gradient wind speeds are usually measured over a 10-minute duration. Any any given location, wind speed increases with height in what is known as the boundary layer, up till a certain point, beyond which wind speed does not increase. The minimum height for measuring the gradient wind speed is the thickness of that boundary layer, usually in the order of 1 kilometer.
Hail storms can cause severe damage to property and agriculture.
A warning issued by the NHC whenever a hurricane is expected to make landfall, or a combination of dangerously high water and very rough seas, are expected in a special coastal within the next 24 hours or less. Precautionary actions and evacuation follow immediately. An indication from the NHC whenever a hurricane is expected to make landfall within the next 36 hours. Everyone in the area covered by the hurricane watch is expected to listen for further advisories and be prepared to act promptly if a hurricane warning or evacuation order is issued. Hurricanes are large circulating windstorms covering hundreds of miles forming over warm oceans.