Saturday, August 13, 2016

Tropical Terminology



Invest - When a tropical weather center (like the National Hurricane Center) is interested in collecting special datasets for an area of disturbed weather, they call it an "invest," because they are investigating the system for potential development. The designation of "invest" doesn't correspond to any likelihood of development, but it does mean there's an area of disturbed weather, and the organizations are looking into it.

Tropical Cyclone - A generic term for warm-core weather systems that occur in the tropics, like tropical storms and hurricanes.

Tropical Depression - A tropical cyclone in which the maximum sustained surface wind speed is less than 39 mph (34 knots).

Tropical Storm - A tropical cyclone in which the maximum sustained surface wind speed ranges from 39 mph (34 knots) to 73 mph (63 knots).

Hurricane - A tropical cyclone in which the maximum sustained surface wind is 74 mph (64 knots) or more.

Major Hurricane - A hurricane with winds greater than 111 mph (category 3 or higher on the Saffir Simpson hurricane wind scale).

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 surge can reach heights well over 20 feet and can span hundreds of miles of coastline.

Hurricane Warning - An announcement that hurricane conditions (sustained winds of 74 mph or higher) are expected somewhere within the specified area. Because hurricane preparedness activities become difficult once winds reach tropical storm force, the hurricane warning is issued 36 hours in advance of the anticipated onset of tropical-storm-force winds.

Hurricane Watch - An announcement that hurricane conditions (sustained winds of 74 mph or higher) are possible within the specified area. Because hurricane preparedness activities become difficult once winds reach tropical storm force, the hurricane watch is issued 48 hours in advance of the anticipated onset of tropical-storm-force winds.

Tropical Storm Warning - An announcement that tropical storm conditions (sustained winds of 39 to 73 mph) are expected somewhere within the specified area within 36 hours.

Tropical Storm Watch - An announcement that tropical storm conditions (sustained winds of 39 to 73 mph) are possible within the specified area within 48 hours.

Short Term Watches and Warnings - These watches/warnings provide detailed information about specific hurricane threats, such as flash floods and tornadoes.

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