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Unorganized mass of thunderstorms that lasts for more than 24 hours. Very little, if any, organized wind circulation.
Closed wind circulation around a center with sustained wind from 20-34 knots (23-39mph).
Distinct circulation. Maximum sustained winds are from 35-64 knots (40-74mph). The storm is named once it reaches this strength.
Pronounced circulation. Maximum sustained winds exceed 64 knots (74mph).
Catagory One Hurricane
Minimal Hurricane. Winds of 64-83 knots (74-95mph). Minimum surface pressure is higher than 980mb. Storm surge of 3-5 feet.
Catagory Two Hurricane
Moderate Hurricane. Winds of 84-96 knots (96-110mph). Minimum surface pressure is between 979-965mb. Storm surge of 6-8 feet.
Catagory Three Hurricane
Extensive Hurricane. Winds of 97-113 knots (111-130mph). Minimum surface pressure is between 964-945mb. Storm surge of 9-12 feet.
Catagory Four Hurricane
Extreme Hurricane. Winds of 114-135 knots (131-155mph). Minimum surface pressure is between 944-920mb. Storm surge of 13-18 feet. Example: Hurricane Andrew (1992).
Catagory Five Hurricane
Catastrophic Hurricane. Winds greater than 135 knots (155mph). Storm surge greater than 18 feet. Example: Hurricane Mitch (1998).
Issued when winds of 39-54 mph are expected.
Issued for a coastal area when there is a threat of hurricane conditions within 24-36 hours.
Issued when hurricane conditions are expected within 24 hours or less. Includes winds of 74mph and/or dangerously high tides and waves. Take action immediately.
Flash Flood Watch
Flash flooding possible...stay alert.
Flash Flood Warning
Flash flood imminent. Take action immediately.
Tornadoes are possible in your area. Remain alert for approaching storms.
Tornado has been sighted or indicated by weather radar. Take action immediately.
Severe Thunderstorm Watch
Severe thunderstorms are possible in your area. Tornadoes possible in or around this area.
Severe Thunderstorm Warning
Severe thunderstorms are occuring. Tornadoes possible in or around this area.
Fujita Tornado Scale (F-Scale)
Classification system for tornadoes. Developed in 1971 by Dr. Theodore Fujita.
Minimal Tornado. Winds of 40-72mph. Frequency: 29%.
Moderate Tornado. Winds of 73-112mph. Frequency: 40%.
Major Tornado. Winds of 113-157mph. Frequency: 24%.
Severe Tornado. Winds of 158-206mph. Frequency: 6%.
Devastating Tornado. Winds of 207-260mph. Frequency: 2%.
Incredible Tornado. Winds of 261-318mph. Frequency: less than 1%.
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