Watching a hurricane can be both captivating and terrifying. With hurricane season starting June 1 in the Atlantic and Central Pacific, and May 15 in the Eastern Pacific, you may want to learn more about how these massive storms work. These weather systems, as large as 1,000 miles in diameter, present three threats: winds destructive enough to tear apart buildings, storm surges that can swamp coastal areas and push water miles inland, and torrential rains that can cause devastating flooding. Follow along with these graphics to learn more about the birth and devastating power of these swirling ocean storms.
Hurricanes are born in the tropics, above warm water. Clusters of thunderstorms can develop over the ocean when water temperatures exceed 80 degrees Fahrenheit. If conditions are right, the clusters swirl into a storm known as a tropical wave or tropical depression.
A tropical depression becomes a named tropical storm once its sustained wind speeds reaches 39 miles per hour. When its winds reach 74 mph, the storm officially becomes a hurricane.
To truly understand how a hurricane forms, you need to look inside these massive storms.
A hurricane has three main parts:
The eye is the calm, low-pressure center of the storm, usually about 30 miles in diameter. Winds are low to nonexistent.
The eyewall surrounds the eye and contains the strongest winds and rain. Winds can reach 200 mph.
Rain bands are surrounding clouds and thunderstorms that spiral inward.
Inside the hurricane, warm, humid air swirls inward around the eye, speeding up as it approaches the center. Air also rises outside the eyewall, under the bands of thunderstorms around the hurricane.
These thunderstorm bands are typically 3 to 30 miles wide and 50 to 300 miles long.
A hurricane’s size tends to be determined by the size of the initial disturbance, but other factors can contribute, including moist and unstable surrounding conditions or dramatic changes in the eyewall.
When thunderstorm activity begins to organize in spiral bands near the center, low-level air converges toward the center, with nowhere to go but up. As that air reaches the top of the storm, some flows outward and some descends in the center, releasing heat and clearing out an eye.
The warming air causes the pressure to fall, fueling the cycle of spiraling inflow and rising air in the developing eyewall. That leads to even more descending air, lower pressures and faster winds.
While the destructive winds of a hurricane are feared, hurricane storm surges can be even more deadly.
In open ocean, hurricane winds push water toward the center of the storm. The water spirals downward into the ocean, creating underwater currents.
As the hurricane approaches shallow water near land, the ocean floor blocks the water from flowing away and causes the rise in water level known as storm surge.
The higher water surges inland, topped by large, battering waves. The surge can raise water levels on rivers miles inland from the point of landfall. Factors that influence the height of storm surge:
Storm intensity and angle. Stronger winds produce higher surge, and a storm making a perpendicular landfall is likely to produce higher surge.
Shape of the ocean floor and coast. Gently sloping continental shelves make the coast more vulnerable to water piling up.
Height and speed. A storm produces a higher surge on an inward-curving coast than an outward-curving coast. A fast-moving storm produces higher surge on an open coast, but a slower storm produces a bigger surge when it’s approaching a bay.
Timing. Water levels rise higher when a hurricane arrives during high tide.
Wind categories are described using the Saffir-Simpson Hurricane Wind scale, based only on a storm’s sustained wind speeds:
Track the latest hurricanes with our Hurricane Tracker
When the National Hurricane Center is tracking a storm, watch its progress here:
SOURCE Live Science; NASA; University of Illinois; University Corporation for Atmospheric Research
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