Hurricanes are the only storm systems on Earth that require warm water to form and consistently develop an “eye” in their center as they gain strength. These are some basic hurricane facts; however, it’s time to dig deeper and look at how these giant tropical cyclones take shape and how their parts fit together.
How Do Hurricanes Form?
A hurricane is a tropical cyclone that converts heat energy into wind, requiring warm ocean air and light surface winds surrounding an area of developing low pressure. Hurricanes often begin as a patch of thunderstorms. This system graduates to a concentrated area of tropical storms with falling pressures and winds increasing to 74 mph where the classic hurricane eye forms. Here’s a better look into the hurricane development stages.
Early Stage — Low Pressure
Warm ocean water over the tropics heats the air above it, causing it to rise and swirl into an area of low pressure. Some of these whirls will grow into a tropical cyclone (depression, storm, or hurricane) if surface pressures drop and thunderstorms gather around the center. This early stage is a process that may take 2 or 3 days.
Intermediate Stage — An Eye Forms
A tropical storm becomes a hurricane when maximum sustained winds reach 74 mph or greater. Most hurricanes develop an eye by the time winds reach 85 or 90 mph. A well-defined eye, warm water, open seas, and light atmospheric winds help the storm continue gathering strength.
Intense Stage — Major Hurricane
The National Hurricane Center defines a major hurricane as one having maximum sustained winds of 111 mph or more, meaning Category 3 or greater. Intense hurricanes are characterized by a well-developed eye, a steady supply of warm ocean water, and strong high-level outflow above the storm. About 40% of Atlantic Basin hurricanes reach Category 3 or stronger.
4 Parts of a Hurricane
A hurricane is a giant engine that converts heat energy to wind energy; the storm’s structure causes surface pressures to drop so the wind can spiral into the storm more quickly. Each piece forms a giant engine that makes hurricanes a fearsome force of nature.
1. The Eye
Strong hurricanes always have an “eye” near the center of the cloud pattern. The eye contains the lowest pressure in the storm:
The lower the pressure in the eye, the faster the wind around it. Higher winds make for deeper and deadlier storm surges when the hurricane strikes the coast.
The eye of a hurricane is often free of clouds and can be seen as a dark spot on storm satellite images — this is because the air in the eye sinks and heats up.
Air drawn in around the eye spins upward 6 to 10 miles vertically into the air before it spreads outward in a clockwise fashion, venting the storm and maintaining its strength.
2. Eyewall
The relative calm of the eye is surrounded by a violent whirl of air filled with intense thunderstorms; this is the eyewall. The eyewall contains the highest winds in the entire hurricane along with torrential rain of several inches per hour. It is the most dangerous part of the hurricane and where the storm surge reaches its maximum.
3. Rain Bands
The low pressure in the eye of a hurricane draws air inward in a counterclockwise flow for hundreds of miles around the system; this flow creates long, thin lines of thunderstorms extending outward from the storm center — they’re called rain bands or spiral bands. Hurricanes often produce tornadoes once they are over land, and the spiral bands are responsible for most of them.
4. Hurricane Outflow
A major hurricane looks like a pinwheel from space as the airflow spirals into the center at lower altitudes and outward at higher altitudes. The outflow is essential to vent the storm and balance incoming air versus outgoing air. If the outflow weakens the hurricane will begin to lose strength.
Where Do Hurricanes Form?
Hurricanes usually form over warm ocean water where winds are weak aloft. The period from June to November is called “Hurricane Season,” and while hurricanes can (and do) form in other months, more than 90% of them take place during the season. Hurricane breeding grounds shift, starting early on in the Gulf of Mexico, expanding to cover most of the tropical Atlantic at season’s peak and ending late-season back in the Gulf. As well as the Gulf, Hurricanes can also form along fronts stalled on the U.S. East Coast.
The Sahara Desert’s vast blanket of heat is a breeding ground for weak low pressure cells — several of these Saharan lows develop into tropical storms or hurricanes each year that threaten North America. Examples include Hurricane Andrew in 1992, one of the strongest hurricanes ever to strike the U.S., and Hurricane Ike in 2008.
Regardless of where you live, make sure you’re up to date on the latest hurricane safety tips if a hurricane develops in your area.
Keep Track of Hurricanes From Anywhere
Your AcuRite home weather station will allow you to observe at-home readings, even if you have to evacuate to avoid a hurricane. You can keep tabs on what’s happening in your backyard through real-time home weather station reports viewed on your phone or PC, anywhere there’s internet access. We can only hope your weather monitor will never find itself performing such a task, but if it does, you can know what to expect when you return.
Steve LaNore is a certified broadcast meteorologist with more than 30 years of forecasting and technical experience. He has provided meteorological consulting for everything from insurance adjusters to court cases and is a nine-time award-winning author and broadcaster. LaNore has authored two books, available on Amazon. He resides in north Texas near beautiful Lake Texoma.