What are Cyclones and How do They Form

Hurricanes, cyclones, and typhoons are all the same weather phenomenon, each classified depending on where they occur.

  • In the Atlantic, the storms are called hurricanes.
  • In the northwestern Pacific, the same powerful storms are called typhoons.
  • In the southeastern Indian Ocean and southwestern Pacific, they are called severe tropical cyclones.
  • In the northern Indian Ocean, they’re called severe cyclonic storms.
  • In the southwestern Indian Ocean, they’re just called tropical cyclones.
  • To be classified as a hurricane, typhoon, or cyclone, a storm must reach wind speeds of at least 74 miles an hour.
  • If a hurricane’s winds reach speeds of 111 miles an hour, it is upgraded to an “intense hurricane.”
  • If a typhoon hits 150 miles an hour, as Usagi did in 2013, then it becomes a “super-typhoon.”
  • While the Atlantic hurricane season runs from June 1 through November 30, the typhoon and cyclone seasons follow slightly different patterns.
  • In the northeastern Pacific, the official season runs from May 15 to November 30.
  • In the northwestern Pacific, typhoons are most common from late June through December.
  • The northern Indian Ocean sees cyclones from April to December.

Hurricanes, typhoons, and cyclones form where there is cold air high above a warm ocean, typically near the equator, where ocean water is warm enough. When the ocean is warm, the water heats the air directly above it, causing ocean water to evaporate up into the air. When this warm wet air rises, it creates thick, heavy clouds that push cold air even higher and sideways. When assisted by additional wind, it can begin to spin around, picking up more and more air and water, that’s when it starts to become a hurricane.

A hurricane starts out as a tropical disturbance. A tropical disturbance sometimes grows into a tropical depression. This is an area of rotating thunderstorms with winds 38 mph or less. A tropical depression becomes a tropical storm if its winds reach 39 mph. The tropical storm becomes a hurricane if its winds reach 74 mph.


Once a hurricane forms, weather forecasters predict its path. They also predict how strong it will get. This information helps people get ready for the storm. There are five types, or categories, of hurricanes. The scale of categories is called the Saffir-Simpson Hurricane Scale. The categories are based on wind speed.

  • Category 1: Winds 119-153 km/hr (74-95 mph) – faster than a cheetah
  • Category 2: Winds 154-177 km/hr (96-110 mph) – as fast or faster than a baseball pitcher’s fastball
  • Category 3: Winds 178-208 km/hr (111-129 mph) – similar, or close, to the serving speed of many professional tennis players
  • Category 4: Winds 209-251 km/hr (130-156 mph) – faster than the world’s fastest rollercoaster
  • Category 5: Winds more than 252 km/hr (157 mph) – similar, or close, to the speed of some high-speed trains

What Are the Parts of a Hurricane?

  • Eye: The eye is the “hole” at the center of the storm. Winds are light in this area. Skies are partly cloudy, and sometimes even clear.
  • Eye wall: The eye wall is a ring of thunderstorms. These storms swirl around the eye. The wall is where winds are strongest and rain is heaviest.
  • Rain bands: Bands of clouds and rain go far out from a hurricane’s eye wall. These bands stretch for hundreds of miles. They contain thunderstorms and sometimes tornadoes.

How Are Hurricanes Named?
There can be more than one hurricane at a time. This is one reason hurricanes are named. Names make it easier to keep track of and talk about storms.

A storm is given a name if it becomes a tropical storm. That name stays with the storm if it goes on to become a hurricane. (Tropical disturbances and depressions don’t have names.)

Each year, tropical storms are named in alphabetical order. The names come from a list of names for that year. There are six lists of names. Lists are reused every six years. If a storm does a lot of damage, its name is sometimes taken off the list. It is then replaced by a new name that starts with the same letter.

Why are Hurricanes so dangerous?

While hurricanes are categorized based on their wind speeds, wind isn’t typically the most dangerous part of such storms. It’s actually the storm surge, the storm surge is the bulge of water built up in front of a cyclone or hurricane courtesy of its winds.

It’s the number one killer in hurricanes, that’s what killed people in Katrina, it’s what killed people in Sandy and in Haiyan.

Flash flooding caused by intense rains is also a major killer, Hurricane Mitch in 1998 killed 12,000 people and it was all from flash flooding.

Climate change will likely increase the frequency of high-end hurricanes and those powerful storms have the potential to produce a lot of rain, flooding, and strong storm surges.

Top 10 Deadliest Hurricanes

10. Hurricane Andrew

This powerful Category 5 hurricane walloped South Florida, mainly the area south of Miami, in August 1992. Storm season started quietly that year with minimal activity — even Andrew was originally considered a “weak” formation when it developed in the Atlantic Ocean — but ended with a bang. By the time it hit the Bahamas, this first-named storm of the season sent winds whipping at more than 160 mph (257 kph).

In Florida, Andrew demolished scores of homes, exposing what experts later determined was a flimsy and under-enforced housing inspection code. It turned low-lying streets into waterways and killed 15 people. The storm also left drivers to fend for themselves for weeks, as roughly 9,500 traffic signs and signals were destroyed.

With damage estimated at $26.5 billion, Andrew was the costliest hurricane in U.S. history for more than a decade. One positive legacy was that the South Florida building code was entirely revamped and now all new homes are required to have storm shutters or impact-resistant glass; roofs have enhanced nail requirements, too.

9. Hurricane Hugo

Florida and the Gulf of Mexico coast often bear the brunt of hurricane traffic in the U.S., but coastal dwellers to the north have also seen their share of storm-related destruction. Hurricane Hugo was one of the most fearsome storms to hit the Carolinas, causing 50 deaths and about $8 billion in damage in the U.S. and Caribbean.

The massive storm was classified as a Category 3 hurricane as it approached Charleston from Puerto Rico in late September 1989 but intensified to a Category 4 storm before making landfall on Sullivan’s Island, S.C. With winds clocking in at 135 mph (217 kph), Hugo was the strongest storm to hit the east coast north of Florida since Hurricane Hazel in 1954. The storm also moved quickly — at nearly a 30 mph (48 kph) clip — causing significant damage in inland areas after passing north of Charleston.

8. Hurricane Sandy

After barreling through Jamaica, Cuba, and Haiti, the huge, slow-moving storm weakened to a post-tropical cyclone before making U.S. landfall in October 2012. But it was strong enough to wreak havoc on New York City and the Jersey Shore. Storm surges of more than 13 feet (4 meters) left parts of lower Manhattan under water and residents across the borough without power for days. Meanwhile, parts of Staten Island and beaches in Queens were nearly wiped off the map.

Sandy destroyed or damaged about 650,000 homes in the Northeast region and killed 117 people in the U.S. alone, as well as 69 others in Canada and the Caribbean. At $65 billion and climbing, Hurricane Sandy was the second-most costly hurricane in U.S. history. The hurricane is also referred to as “Superstorm Sandy” because as it approached New York it had the characteristics of a winter storm rather than a tropical one.

7. Hurricane Camille

Andrew is one of only three Category 5 hurricanes to hit the U.S. since 1900. Another was Camille, a nasty storm that brought heavy flooding and 200-mph (320-kph) winds to the Gulf Coast and later Virginia. After forming near the Cayman Islands in August 1969, the storm first blew through Cuba at a Category 3 level and later intensified on its way to Mississippi. It weakened to a tropical storm before it reached Virginia, but Camille continued to pour upward of 20 inches (51 centimeters) of rain as well as flash flooding and mudslides on a region just 120 miles (193 kilometers) from the nation’s capital. The storm resulted in 256 deaths and more than $1.4 billion in damage.

Camille played an important role in hurricane tracking in that it spawned the creation of the Saffir-Simpson Hurricane Wind Scale, which ranks storms from categories 1 to 5 based on wind speed. Category 1 hurricanes blow winds ranging from 74 to 95 miles (119 to 153 kilometers), while those in the Category 5 range feature wind speeds of more than 156 miles (251 kilometers) an hour. The system is designed to give residents in danger zones a better idea of what to expect from a brewing storm.

6. Hurricane Gilbert

There are many ways to measure a hurricane, whether wind speed and rain or lives lost and property damage caused. Then there’s sheer size. With a 500 nautical mile (926 kilometers) diameter, Gilbert was one of the largest hurricanes ever observed in the Atlantic basin. The storm originated near the Cape Verde Islands on the west coast of Africa, the birthplace of some of the worst hurricanes in history, including Andrew.

After becoming a Category 5 storm in September 1988, Gilbert literally covered the entire island of Jamaica, damaging roughly 80 percent of the island’s homes. The hurricane then moved on to the Cayman Islands and Mexico, among other areas, before weakening and crossing into Texas, manifesting itself in a series of tornadoes. The storm caused 318 deaths, including 200 people killed in flooding in Mexico and 28 who died when a Cuban freight ship was thrown into a shrimp boat. Gilbert-related damage topped out at about $5.5 billion.

 5. 1935 Florida Keys Labor Day Hurricane

This Category 5 storm, considered the strongest to hit the U.S. in the 20th century, brought 200-mph (320-kph) winds and soaking rain to the upper and middle Florida Keys and killed approximately 400 people. More than half of the dead were World War I veterans who had been working on building a highway from Key West to Key Largo. Damage in the United States was estimated at $6 million.

This storm is simply known as the “Labor Day Hurricane” because the practice of naming hurricanes didn’t begin until 1953. (And the World Meteorological Organization gave storms only female handles until 1978.) The storm also struck well before advances in weather tracking technology, including the regular use of Doppler radar, that predict where a storm might end up, leaving residents largely in the dark as the hurricane approached. Many of the victims had waited anxiously for an evacuation train that never came – it was washed away from the tracks.

4. Hurricane Katrina

Hurricane Katrina is often referred to as a man-made, rather than natural, disaster by those who fault infrastructure problems for the decimation caused by this storm that ravaged New Orleans and other parts of the Gulf Coast.

On Aug. 26, Katrina looked like a hurricane that was fizzling out, but it began rapidly strengthening to Category 5 levels over warm water in the Gulf. By Aug. 28, a mandatory evacuation order was issued for New Orleans. As the now-Category 3 hurricane reached the city, water topped over its systems of levees causing them to break and the streets to flood. Eventually, 80 percent of the city was underwater.

Katrina left residents who couldn’t or chose not to evacuate stranded in their homes with waters rising around them. Forty percent of hurricane-related deaths were from drowning. Slow federal government reaction to the plight of those affected led to claims of incompetence and even deliberate disregard for poor and black people.

In all, Hurricane Katrina claimed 1,833 lives and at $108 billion is considered the costliest hurricane in U.S. history. The Federal Emergency Management Agency calls it “the single most catastrophic natural disaster in U.S. history”.

Katrina also displaced 400,000 people to areas like Houston and Atlanta. Many never returned to New Orleans. An upgraded system of levees was completed in 2013, but officials are worried about the massive cost of maintaining them with a shrunken tax base.

3. The Galveston Hurricane

Katrina was terrible, but it’s not the worst storm in the Gulf Coast. The Galveston Hurricane of 1900 took an estimated 6,000 to 12,000 lives, mostly in Texas, in September 1900 and is considered the deadliest hurricane in U.S. history.

The storm didn’t become a hurricane until passing west of the Florida Keys where a sharp left turn sent it heading straight toward Galveston. That gave residents and local officials less than four days to prepare. The Category 4 storm brought 20-foot (6-meter) storm surges and flash flooding and even pounded Oklahoma and Kansas when it was done with Texas. More than 3,600 homes, as well as a number of structures believed to be “storm proof”, were destroyed in the hurricane, whose damage totaled $30 million.

Galveston took some amazing steps to ensure the damage was not repeated. It built a 3.5 mile, or 5 kilometers, seawall (later extended to 10 miles or 16 kilometers) and raised the level of the entire city, in some places as much as 16 feet (5 meters).

2. Hurricane Mitch

Mitch might not have received as much attention in the U.S. as Sandy and Katrina, but the death and devastation this hurricane caused exceeded some of history’s better-known storms. The slow-moving hurricane seemingly paused once it reached Honduras in October 1998, pouring up to 4 inches (10 centimeters) of rain an hour for two days, causing mudslides and deadly flooding along the way.

With approximately 11,000 people dead (and thousands more missing), Mitch is the second-deadliest hurricane on record and the worst to hit the Western Hemisphere in more than 200 years. The storm caused more than $5 billion in damage in Honduras, where much of the country’s infrastructure and crops were completely destroyed. Nicaragua was also devastated by Mitch, losing 2,000 people in one mudslide alone.

1. The Great Hurricane of 1780

The United States as we know it was just a gleam in George Washington’s eye when the Great Hurricane of 1780 blasted its way through the Caribbean, killing approximately 22,000 people. Among the dead were British and American soldiers who had been skirmishing in warships scattered throughout the region as part of the Revolutionary War.

While there isn’t much data on record regarding the hurricane’s speed or rainfall, what we do know is that the storm bombarded several Caribbean islands, including Barbados, Martinique, and St. Lucia over six days in October. One local observer wrote that the hurricane stripped the bark off of trees, which has caused some to speculate the winds must have topped 200 mph (320 kph). This massive storm is considered the deadliest hurricane of all time.