Hurricanes: Formation, Structure and Measurement

Weather Knowledge

LITTLE ROCK, Ark. – June 1 is the official start to the Atlantic Hurricane Season. From June 1 through November 30, tropical systems including hurricanes are most likely to form over oceans in the Northern Hemisphere.

Hurricanes are very complex system, from the way they form to the storm’s structure. To better understand these tropical systems, we broke down some key elements.

HURRICANE FORMATION:

As the temperature of water in the ocean rises, hurricane development is more likely to occur. A tropical wave typically denotes the beginning of what could lead to hurricane formation as it moves over warm ocean water. Warm air rises and condenses, forming clouds and thunderstorms. As water condenses and forms droplets, the system releases heat to power the storm.

Not only does a tropical system need warm water to thrive off of, but it also requires low wind shear to keep its strength. If a tropical system travels through an area where there’s a large difference in wind speed or direction, it can weaken.

As the low continues traversing the ocean waters, the storm system grows in size and strength. It becomes a tropical storm when winds range from 39 to 73 mph. When wind speeds reach 74 mph, the system is officially classified as a hurricane.

HURRICANE STRUCTURE:

Once a tropical system has reached hurricane status, its structure is clearly defined. Using satellite imagery, you can see the eye, eyewall and rainbands.

In the eye of the storm, the winds are slowest. In this area, air is sinking and there is a lack of cloud cover often revealing a clear sky. Just beyond the eye is the eye wall, where the winds are the strongest within the tropical system. Beyond the eye wall is where the rainbands are located. Rainbands are curved lines of storms that swirl in motion around the tropical system itself. Due to the spin of the system and friction over land, rainbands can sometimes spur spin-up tornadoes within them.

While hurricanes are powerful tropical systems, not all areas of the storm are equally as strong as the others.

If you slice a hurricane into four equal quadrants, the front right quadrant is the most destructive area of the storm in the Northern Hemisphere. The forward motion of the hurricane adds to the strength of the counter-clockwise winds within the system, leading to higher wind speeds and greater storm surge.

HURRICANE MEASUREMENT:

Every hurricane is given a different category number based off wind speed. The Saffir-Simpson scale is used to give a one to five rating of the hurricane to estimate potential property damage.

Saffir-Simpson Hurricane Wind Scale:

Category 1: 74-95 mph
Category 2: 96-110 mph
Category 3: 111-129
Category 4: 130-156
Category 5: 157+

NAME BY REGION ACROSS THE WORLD:

Three different terms are used to decribe this weather phenomenon globally.

In the northern Hemisphere, east and west of North America, the term “hurricane” is used to define this storm system. In the southern hemisphere, the term “cyclone” is used to describe the tropical system. In the western Pacific Ocean, near Asia, the term “typhoon” is most often used.

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