Hurricanes are tropical cyclones that form in the Western Hemisphere and the Atlantic Ocean. Tropical cyclones are the most complex and powerful storm systems on Earth. They pack all the hazards of the planet's atmosphere: torrential rain, lightning, hail, high-speed winds and tornadoes. And they all begin with calm winds swirling over very calm, warm waters.

Below, we’ll go over some facts about hurricanes, like how they're formed, how big they can get, and how much damage they can leave in their wake..

As seen in the image above, hurricanes in the Pacific Ocean form in the waters off the western coast of Mexico and often move northwest, further into the ocean. Hurricanes that do head to the U.S. often lose strength or dissipate before reaching the West Coast due to cooler water and upper-level wind shears. Hurricanes in the Atlantic Ocean, however, often pose a much greater threat. This is greatly due to the dry, hot winds that are blown westward from the Sahara desert.

What causes a hurricane?

Steps to a hurricane's formation:

1. Some of this hot, dry air evaporates the warm sea surface water in the Atlantic Ocean and forms clouds. More heat energy collects and builds more clouds. Moving westward, it becomes a tropical wave.
2. Warm air rises, cool air sinks. This circulation intensifies, pulling in more moist warm air. The system strengthens into a tropical depression. If the storm passes over calm, warm water, there is a good possibility that it will grow to be a tropical storm.
3. In rushing air brings more heat energy to the system. Water condenses out of the clouds as rain. At 74 mph, the storm develops an eyewall (a hollow, calm spot in the storm's rotation). It now becomes a Category 1 hurricane.

How big are hurricanes?

On average, the diameter of hurricane-force winds is about 100 miles. Slower speed winds further out from the storm center increase the storm system's diameter on average 300 to 400 miles across. And the eye of the hurricane is 30 miles in diameter.

How dangerous is a hurricane?

A hurricane is dangerous no matter its size or strength. A hurricane's high winds, storm surges, heavy rains and tornadoes all pose a threat to anything in the hurricane's path. While that path varies from hurricane to hurricane, it is often the coastal states with heavily populated areas that bear the brunt of the destruction.

Hurricane-force wind strength is rated according to the Saffir-Simpson Hurricane Wind Scale. This scale estimates potential property damage according to the hurricane's sustained wind speed.

Category 1: 75-95 MPH - Very dangerous. Well-constructed frame homes could have damage to the roof, or tree branch damage. Some power loss.

Category 2: 96-110 MPH - Extremely dangerous. Homes sustain major roof and siding damage. Shallow-rooted trees snapped or uprooted. Near-total power loss is expected.

Category 3: 111-129 MPH - Devastating damage. Major damage to house roof decking. Many trees uprooted or snapped. Electricity and water will be unavailable for several days or weeks.

Category 4: 130-156 MPH - Catastrophic damage. Many homes can be severely damaged. Most trees snapped or uprooted. Power outages can be extensive, lasting weeks to months.

Category 5: 157+ MPH - Catastrophic damage. Most homes are destroyed. Most of the area will be uninhabitable for weeks or months.

Storm surge

In addition to high winds, a hurricane causes high tides. A normal ocean tide is about two feet tall. But when storm winds push up against the ocean surface, pulling up seawater, this forms a storm surge that piles on top of the normal tide. If a hurricane's winds add 15 feet on top of the normal 2-foot ocean tide, this produces a 17-foot storm tide, which can very easily sweep away buildings, trees, cars, and people.

Storm tide height also depends on whether the tide is high or low. The worst case is when a hurricane has generated a storm tide during a normal high tide. High tides carry storm surges higher and help send them further inland.

What are the warning signs of a hurricane?

Since hurricanes develop in the ocean, it's easy to detect the oncoming of a hurricane before it hits inland. Weather forecasters will know several hours to several days before the arrival of a hurricane, providing ample time for preparation. Make sure to follow your local weather news channel for alerts.

Decide if you are going to take shelter in place or evacuate.

Take shelter:

• Prepare your disaster supplies kit.
• Locate a safe room in your home, preferably in the basement or under a room under the stairs, stay away from windows.
• Adjust refrigerator temperatures to the coldest settings to reduce the potential for food spoiling if the power is temporarily lost.
• Fully charge all your phones.
• Determine escape routes from your home and a nearby place to meet, these places should be measured in tens of miles.
• Don't leave cars parked under trees.
• Check to make sure pool covers are secure.
• Bring in plants, flags, house ornaments, outdoor furniture, and anything else that could be potentially hazardous.
• Make sure to have enough flashlights and batteries, stay away from candles as these could start a fire.

Evacuate:

• Remove fuses from the air conditioning system to prevent damage.
• Turn off water to prevent flooding from broken pipes.
• Turn off the gas to prevent leaks from occurring

When to consider evacuation from a hurricane:

• Local authorities have advised evacuation for your area.
• If you live on a barrier island with a history of storm surge damage.
• If you live in a low-lying or flood-prone area.
• If you live in a mobile home in a coastal area.
• If your home is in a coastal area and lacks hurricane structural reinforcements.
• If you are vacationers with young or elderly dependents.

What to do during a hurricane:

• Monitor the radio or television for weather conditions and updates.
• Do not go outside, even if the storm seems to have subsided. This may be the eye of the storm hitting landfall, which means strong winds and rain will resume shortly.
• Stay away from all windows and exterior doors and take shelter in a small, windowless room.
• If power is lost, turn off all major appliances to reduce the chances of damaging a power surge.
• Do not handle electrical equipment and do not use a landline unless it's an emergency.

What to do after a hurricane:

• Listen to local officials for updates and instructions on what to do.
• Avoid debris and downed, damaged or loose power lines.
• Return home only when authorities have declared the area safe.
• Avoid walking or driving through flood waters.
• When power returns to your home, do not start all major appliances at once. Turn them on gradually to reduce damage to sensitive equipment.
• Even if you have ventilation, never use a generator indoors. This includes garages, basements and crawlspaces. Exhaust fumes contain high levels of carbon monoxide which can be deadly if inhaled. Even when left outside, keep generators away from doors and windows and at least 10 feet away from your home. Also, allow your generator to cool off before refilling it with gas – splashing gas on hot generator components can lead to a fire.
• Never use charcoal indoors because burning charcoal produces high levels of carbon monoxide that can reach lethal levels in enclosed spaces.

Sources

Buis, Alan. "Could a Hurricane Ever Strike Southern California?" Jet Propulsion Laboratory - California Institute of Technology, NASA, 17 Oct. 2012, Jet Propulsion Labratory at NASA. 

"Saffir-Simpson Hurricane Wind Scale." National Hurricane Center, National Oceanic and Atmospheric Administration, Saffir-Simpson Hurricane Wind Scale. 

"Storm Surge Overview." National Hurricane Center, National Oceanic and Atmospheric Administration, Storm Surge Overview.