Definition of a Hurricane
The National Hurricane Center defines hurricane as:
“A tropical cyclone in which the maximum sustained surface wind (using the U.S. 1-minute average) is 64 knot (74 mph or 119 km/hr) or more. The term hurricane is used for Northern Hemisphere tropical cyclones east of the International Dateline to the Greenwich Meridian. The term typhoon is used for Pacific tropical cyclones north of the Equator west of the International Dateline.”
In more general terms a hurricane is a violent storm. It is characterized by sudden changes of the wind, heavy rain, thunder, and lightning.
These cyclones develop from areas of low pressure and thunderstorms over the warm seawater. The thunderstorms give off heat that warms the atmosphere. Air rises and the barometric pressure falls even more. As the air pressure drops, winds increase, and a tropical depression may form.
When steady winds reach 39 miles an hour, the cyclone is called a tropical storm and it gets a name. If winds reach a speed of 74 miles an hour inside the tropical cyclone, we call it a hurricane.
Hurricanes begin near the equator, sometimes as distant as Africa. Air begins to form in patterns of rotation as it rises over tropical waters in the ocean. The heat and moisture of late summer fuel storms winds start moving them westward.
The Hurricane Season
Hurricane season in the Atlantic begins June 1st and ends November 30th. The Eastern Pacific hurricane season begins May 15th and also ends November 30th. It is in this time period that weather conditions come together to form swirling tropical cyclones over the Atlantic and Pacific oceans. August and September are peak months during the hurricane season.
How Frequent are Hurricanes?
Each year an average of eleven tropical storms develop over the Atlantic Ocean, Caribbean Sea, and Gulf of Mexico. Many of these remain over the ocean and never impact the U.S. coastline. A single hurricane can last for more than 2 weeks over open waters. They can run a path across the entire length of the eastern seaboard.
Six of these storms become hurricanes each year. In an average 3-year period, roughly five hurricanes strike the US coastline. They kill approximately 50 to 100 people anywhere from Texas to Maine. Of these, two are typically “major” or “intense” hurricanes (a category 3 or higher storm on the Saffir-Simpson Hurricane Scale.
How are Hurricanes Categorized?
Hurricanes are categorized according to the strength of their winds using the Saffir-Simpson Hurricane Scale. A Category 1 storm has the lowest wind speeds, while a Category 5 hurricane has the strongest. These are relative terms, because lower category storms can sometimes inflict greater damage than higher category storms, depending on where they strike and the particular hazards they bring. In fact, tropical storms can also produce significant damage and loss of life, mainly due to flooding.
What Are the Effects of a Hurricane?
Dark skies and growing winds signal the approach of a hurricane. It may appear as a thunderstorm but it can carry storm surges, powerful winds (74 to 160 mph) and torrential rainfalls. Tornadoes can be offshoots of hurricanes, floods and flash floods can follow and swollen rivers water saturated hillsides can lead to landslides. Loss of life from any of these intense weather events is not uncommon.
Over the ocean, wind and large waves created by the storm are a hazard for boats at sea. With modern forecasting and warning systems, boats can steer clear of a hurricane. Before forecasting and warnings were available, hurricanes caused of many shipwrecks. Unlike boats, oil and gas platforms on the water are unable to move out of harms way. Platforms, like those in like in the Gulf of Mexico, can be damaged by the fierce wind and waves.
When a hurricane hits land, tremendous damage can occur to the man-made environment. The amount of damage depends both on the intensity of the storm and what it hits. A combination of winds, storm surge, and rain cause great damage to buildings, power lines, roads, and automobiles. During hurricane Katrina in 2005 levees broke causing much of the city of New Orleans, LA to flood. The damage to the US Gulf coast caused by Hurricane Katrina was the most costly in US history.
Hurricanes cause many changes to the natural environment along a coast too. Sand is eroded from some coastal areas and deposited in others. The waves and storm surge are able to carry large rocks and even boulders. Many low-lying areas are flooded by storm surge. And strong winds and floods can thin or destroy forests.
After a hurricane hits a coastal area, it can travel inland. At this point, the storm has typically weakened, but it can still cause serious damage. Torrential rains from the storm can cause flooding and mudslides.
It is estimated that 10,000 people die each year worldwide due to hurricanes and tropical storms. The majority of human deaths are caused by flooding. Because they can be very dangerous, it is important to look for hurricane warnings and to evacuate if it is recommended in your area.