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Katrina. Sandy. Irene. Andrew. Harvey. These are just a few of the major hurricanes to hit the United States in recent history. A hurricane is a large storm, called a tropical cyclone, that has sustained wind speeds of 74 miles per hour (mph) or higher. 

Hurricanes develop over tropical ocean water. Here, the air at the ocean's surface is warm and humid. It rises to form thunderstorm clouds. As the air rises, it cools. Water vapor condenses into rain and releases energy that fuels the storm. The low pressure system draws more warm air toward the center of the storm, strengthening the cycle. As the atmospheric pressure continues to decrease, wind speeds increase, the storm rotates, and a hurricane is born. There are four stages of hurricane formation:
  1. Tropical Disturbance 
  2. Tropical Depression 
  3. Tropical Storm
  4. Hurricane
Hurricanes can grow to hundreds of miles in diameter. At the center of the storm is the eye, the calm area around which the winds spin. The eye is surrounded by the eyewall, a thin band of the strong, fast winds and heavy precipitation. Most of what we see on images of hurricanes are the feeder bands. Feeder bands are the windy, rainy, spiraling arms of the storm. Hurricanes can be long lasting storms and track over thousands of miles. They will weaken when they no longer have a supply of warm, humid air. This usually occurs as the hurricane moves over cooler ocean waters or passes over land.

The Atlantic Ocean hurricane season is June 1 through November 30. This is the time of year when conditions are most favorable for hurricane formation. However, hurricanes can form outside of those dates. Hurricanes also form over other oceans. Depending on location, these storms are called cyclones or typhoons and have their own storm seasons. Hurricanes are classified by sustained wind speed using the Saffir-Simpson Hurricane Wind Scale shown in the table.

Saffir-Simpson Scale
CategoryWind SpeedDamage
174-95 mph
119-153 km/h
Minimal - roof damage, snapped branches, power line damage
296-110 mph
154-177 km/h
Moderate - major roof and siding damage, uprooted trees, widespread power outages
3111-129 mph
178-208 km/h
Extensive - major exterior damage to houses, electricity outages and water loss
4130-156 mph
209-251 km/h
Extreme - roof and exterior wall loss, extensive tree damage, widespread and long term loss of power and water
5157 mph or higher
252 km/h or higher
Catastrophic - collapsed houses, fallen trees and power poles, areas uninhabitable

Like with any storm, being prepared is key. The good thing about hurricanes is their formation and track is closely monitored well ahead of the storm making landfall. Even so, the exact path of the hurricane can change. Storm surges, or rising ocean water levels, can flood coastal areas and destroy infrastructure. A hurricane watch will be issued 48 hours before hurricane conditions are expected for an area. A hurricane warning will be issued 36 hours before expected hurricane conditions. If a hurricane watch or warning is given for your area, prepare your home and supplies, listen to weather updates, and evacuate immediately if instructed to do so.