Also known as tropical cyclones, hurricanes are a type of severe storm that can wreak havoc on coastal communities around the world.
But storms like this don’t pop up out of the blue. They form under specific conditions then travel across oceans before they make landfall. So what does a hurricane need to form?
For a hurricane to form, there needs to be warm water, warm and moist air, low wind shear, and a tropical location. Combined, these four factors cause thunderstorms to develop on the ocean. If these conditions continue, the storm can begin to rotate and form a massive area of low pressure that becomes a hurricane.
As you can imagine, hurricane development is more complex than these four factors. In this article, we’ll take a closer look at the factors that need to exist for a typhoon to form during hurricane season.
How Do Hurricanes Form?
Before we start talking about the factors needed for a storm to become a hurricane, we first need to discuss how hurricanes form. Already know how hurricanes form? Skip to the next section to learn more about the most important Ingredients for the formation of tropical cyclones
Storms that form hurricanes can begin their lives in any one of a number of different “tropical cyclone basins.” A tropical cyclone basin is simply a common location for hurricane development. For those of us in the United States, the North Atlantic Ocean and the Eastern Pacific are the most important basins to keep an eye on.
During the warmer months of the year, thunderstorms are a frequent occurrence in these basins. If a cluster of these storms groups together and gets strong enough to start rotating around an area of low pressure, they can form a system that’s called a tropical depression.
The rotation of these thunderstorms can cause the local air pressure to drop further, leading to an increased rate of rotation, more energy in the storm, and higher wind speeds. If these wind speeds exceed 74 mph, the storm is classified as a hurricane.
Hurricanes can move fairly quickly from their origins and make landfall at coastal cities where they pack a high sustained wind speed, serious storm surge, dense clouds, and a whole lot of precipitation. Storms from the North Atlantic often end up in the Gulf of Mexico while those in the Eastern Pacific can threaten Hawaiʻi and the western part of Central America.
Ingredients for the Formation of Tropical Cyclones
Now that you understand the basics of hurricane formation, let’s take a look at the key ingredients that are needed to take a small thunderstorm and turn it into a tropical storm:
1. Warm Ocean Water
Have you ever noticed that hurricanes don’t form over land? That’s not a coincidence. Tropical cyclones exclusively start out over ocean waters.
However, they don’t just build up over any ocean—hurricanes need warm ocean water to go from being a minor tropical disturbance to a full-fledged tropical cyclone.
Just how warm, you might ask? Basically, almost all hurricanes start in areas where the surface ocean water is above 78ºF (26ºC). A tropical storm can exist in colder waters, but not for long. That’s because these warm conditions provide crucial energy, moisture, and low-level convergence needed to create areas of low air pressure that drive tropical cyclones.
The fact that hurricanes require warm surface ocean water is one of the many reasons why these storms rarely exist outside of tropical areas. While they can travel far from the equator, hurricanes prefer warm waters and the heat that comes with them.
2. Warm, Moist Air
In addition to warm water, hurricanes love warm, moist air. The reason? Warm, moist air rises, creating areas of divergence aloft. These areas of divergence aloft drive convergence at the surface, drawing more warm, moist air toward the center of the storm and creating a low pressure area over the warm ocean.
Furthermore, as this warm, moist air rises, it usually creates clouds, most of which develop into thunderstorms—especially around the eye of the storm.
Thunderstorms and the increased convection that they bring further pull warm moist air into the center of the storm (called the eye). This initiates a positive feedback loop where groups of individual thunderstorm clouds create low air pressure in the area at the center of the eye wall.
3. Low Wind Shear
If there’s one thing you’ll almost always hear about in a hurricane warning, it’s the storm’s wind speeds. However, while tropical cyclones need to pack winds of more than 74 miles per hour to be classified as hurricanes, these storms require low wind speeds early on in their careers.
Confused? Well, it turns out that areas with high wind speeds are detrimental to tropical depression formation.
That’s because high winds (and in particular, high wind shear) disrupts the organized convection that’s needed for a storm to rotate counterclockwise (in the Northern Hemisphere). Therefore, areas with high wind shear (20 knots or more) rarely ever create hurricanes.
4. Seedling Tropical Location
Last but not least, a tropical cyclone almost always requires a tropical location for its initial formation. While the storm doesn’t have to be located near the equator, it does need to be in a fairly tropical area in order to survive past the tropical depression stage.
This is mostly due to the fact that the warm surface ocean waters needed to create a tropical cyclone are mostly located at low-latitude areas in the Northern Hemisphere and Southern Hemisphere.
Interestingly, however, while hurricanes start near the equator, they rarely ever form on the equator. This is due to the fact that the Coriolis effect is zero at the equator.
Therefore the rotation around the center of the storm that’s integral for hurricane formation is impossible to find at the equator, whether that’s in the Atlantic Ocean or elsewhere. Rather, cyclones search for tropical areas where the Coriolis effect is strong.
Tropical Storm Formation: A True Perfect Storm
Tropical cyclones are a truly amazing type of severe weather. However, for a storm to create something called a tropical cyclone in the first place, it needs warm surface waters, warm and moist air, low winds, and a tropical location.
Here are our answers to your most frequently asked questions about hurricane formation.
What 4 Things Do Hurricanes Need to Form?
To create a hurricane, you need 4 key ingredients: a tropical location, warm surface waters, low wind shear, and moist, warm air. Otherwise the storm won’t build up enough energy to turn into a tropical disturbance and then a hurricane.
What Forms a Hurricane?
Hurricanes are the result of a perfect combination of factors that include heat, moisture, and low winds over warm ocean waters. These storms create their own positive feedback loops where air rises, creates thunderstorm clouds, and drives air toward the center of the system where it can rotate and become a hurricane with winds over 74 miles per hour.