Primer on the Life Cycle of a Tropical Weather Event

As the Atlantic hurricane season heats up, this is a good time to become more familiar with the life cycle of a tropical weather event. How does a mere cluster of rain showers and storms evolve into a major hurricane over time? Here is a closer look at the life cycle of a hurricane.

Various Stages of a Hurricane

A hurricane goes through four defined stages in its life cycle. It is important to know all of the various terminology used by meteorologists when labeling any specific tropical weather event. This knowledge will help you to prepare accordingly if a feature is headed in your direction.

Forecasters use the generic term "tropical cyclone" to describe a low-pressure system that has a defined center of surface wind circulation. In order to qualify as a tropical system, the feature has to be born over tropical or tropical waters. Examples of tropical cyclones include tropical depressions, tropical storms, hurricanes, and typhoons.

While storms that reach the highest degree of intensity in some parts of the world are called typhoons, the term "hurricane" is used to describe the most powerful cyclones that form in the North Atlantic Ocean, the Gulf, the Caribbean Sea, and the eastern North Pacific Ocean.

The first stage of a hurricane's life cycle is known as a tropical disturbance. A disturbance is a mass of clouds, rain showers, and thunderstorms that gets its start in the tropics. Tropical waves are a specific type of disturbance that is characterized by low pressure without a closed loop of wind circulation. These waves typically move from east to west across the tropics, most often originating off the coast of Africa. Although a tropical wave is the common origin of a named feature, there are other ways for these storms to develop.

A tropical disturbance that creates a closed center of circulation is called a tropical depression. These features top out with maximum sustained winds measuring 38 mph or less. This is the widely recognized second stage in a hurricane's life cycle.

The National Hurricane Center (NHC) assigns a name to a feature once it strengthens from a tropical depression into a tropical storm, marking the third stage in the cycle. Tropical storms pack maximum sustained winds between 39 and 73 mph.

The fourth and final stage of the cycle happens when a feature hits the status of a hurricane, defined with maximum sustained winds of at least 74 mph. Once the feature reaches the designation of a hurricane, the NHC then assigns it a specific category based on its wind speeds. The storm is categorized on a scale of 1 to 5, with 5 being the highest. Any storm that falls under the umbrella of a Category 3 or higher storm is known as a major hurricane. This method of defining hurricanes is known as the Saffir-Simpson Scale.

Other Important Terms to Note

In addition to the four primary stages of a hurricane life cycle, forecasters also frequently lean on other terms when referencing tropical weather makers. For example, a potential tropical cyclone (PTC) is a feature that has not yet taken on formal tropical characteristics but poses a threat to land within 72 hours. By assigning the label of a PTC to a feature, the NHC is able to issue watches or warnings so that those in its path have more time to prepare.

The NHC also frequently labels a tropical disturbance as an invest when the cluster of rain showers and thunderstorms bears further monitoring. An invest is showing signs of potentially evolving into a tropical depression or storm. The NHC assigns an invest a number between 90 and 99, followed by a letter that indicates which basin the feature is located. The letter "L" is used to mark the Atlantic while the letter "E" is used to mark the Eastern Pacific. This naming convention works to identify and monitor different areas of concern when multiple features are popping up.

As soon as a disturbance gets the invest label, the NHC then begins to use its specialized data tracking to spit out its famous spaghetti model tracks. These models provide a clearer picture of the potential tracks that the storm could take in the days ahead.

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