How Do Hurricanes Form?

Ever heard the phrase "a storm is brewing"? People use this phrase to communicate that a storm is on the way.

Hurricanes can have different names depending on where they occur. For example, you may have heard them called typhoons or cyclones, and scientists call them tropical cyclones. Technically, only cyclones that form over the eastern Pacific Ocean or the Atlantic Ocean are called hurricanes. However, whatever name we call them, we're constantly referring to the same weather phenomenon. Hurricanes are the most violent storms on our planet and can cause massive destruction to wildlife, buildings, and human beings. But how do they form?

What is a Hurricane? And How Do they form?

Ever heard the phrase "a storm is brewing"? People use this phrase to communicate that a storm is on the way. To brew something, you need a specific mixture of ingredients. For tropical cyclones, the elements required are warm, moist air and wind. For this reason, cyclones only form over areas of the ocean where the water is 80 F (26 C).

To understand how hurricanes form, let's look at an example. Every year, tiny ripples of air travel westward across the African continent towards the ocean. Some of these ripples will become thunderstorms that unleash their fury over the sea. While these storms can be somewhat dramatic, they're not cyclones yet. Instead, the water in the ocean acts as a fuel for the storm because the high levels of moisture in the atmosphere cause the clouds to expand.

Additionally, any crosswinds have to be mild. Otherwise, the clouds will get ripped apart. If they don't get ripped apart in this early stage, the cyclone will continue to get bigger and bigger for days.

Weather scientists break the development of cyclones into four stages:

  1. Tropical disturbance: Water vapor from the warm ocean condenses to form clouds. Through this process, heat is released, and the warm air rises, forming a column pulled into the clouds. The air from around the central column starts to blow inwards to replace the rising air. It is also why cyclones spin! Because our planet is spinning, the air added to the cyclone from the surrounding atmosphere also spins.

  2. Tropical depression: Over time, the cyclone gets bigger and also higher. When this happens, the air at the top of the cloud column cools and becomes unstable. Heat is released in this process (cooling water vapor). It then causes the air at the top of the clouds to get even warmer, adding to the rising air pressure and high winds.

  3. Tropical storm: When the wind speeds reach 39 mph, the tropical depression becomes a tropical storm.

  4. Hurricane: The storm gathers more wind, speed, and clouds as it travels across the ocean. When it eventually reaches speeds of 74 mph, it officially becomes a hurricane.

What Happens When Hurricanes Hit Land?

When hurricanes hit land, they usually weaken because they no longer have the necessary fuel to grow. However, they can cause tremendous damage as they dissipate, depositing large amounts of rainwater and ripping through anything in their path.

We categorize hurricanes based on their wind speed, with higher wind speeds resulting in much deadlier hurricanes. Hurricanes with a 74 to 95 mph speed are classed as category one and typically only cause minimal damage to the surrounding land. Category 2 hurricanes have a wind speed of 96 to 110 mph and cause moderate damage. Category 3 hurricanes travel at 111 to 129 mph and cause extensive landfall damage. By the time we get to category four hurricanes, we're dealing with extreme amounts of damage and wind speeds of 130 to 156 mph. And lastly, category five hurricanes are the most severe of all, traveling at over 157 mph and causing catastrophic damage.

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