Updated: October 13, 2020 03:51 PM
Created: August 06, 2020 01:16 PM
We often hear many terms before we hear the term hurricane, including tropical storm, tropical depression, and a few others, and this naming all refers to the strength of the storm, and the strength of the maximum sustained winds present. A tropical cyclone is the general term we use to describe a low pressure system that develops over tropical or subtropical waters with organized convection and a well-defined center of low pressure.
There are a few stages of development before a tropical cyclone can be called a hurricane. When a tropical wave starts to develop in the North Atlantic, it is first known as an Invest, named by a number 90 through 99 and a letter “L”, representing that this is an area that the National Hurricane Center is investigating for the potential to develop into a tropical depression. A tropical depression forms when an Invest develops into a tropical cyclone with maximum sustained winds speeds of 38 mph or less. Once the maximum sustained wind speeds increase to anything from 39 to 73 mph, it becomes classified as a tropical storm, and anything 74 mph or greater can be classified as a hurricane, with categories 1 through 5 changing as the winds continue to increase.
Second, the water needs to be warm, specifically warmer than 26 degrees Celsius, or 78 degrees Fahrenheit. These warmer ocean temperatures are necessary to encourage evaporation and fuel tropical cyclone intensification, and must extend over a depth of 50 meters creating a deep layer of warm ocean temperatures below the surface.
Next let’s talk about the tropical cyclone’s location. The tropical cyclone must be located at least 5 degrees north or south of the equator. This is necessary because tropical cyclones are known to rotate and spin up, and they get this spin from the rotation of the Earth via the Coriolis force, which is only present further away from the equator. At 5 degrees off the equator and further away, the Coriolis force is strong enough to spin up tropical cyclones and encourage development.
Another necessity for tropical cyclone development is weak vertical wind shear. Vertical wind shear is the difference between the wind speed and wind direction at two different heights in the atmosphere. Because high shear environments typically displace the thunderstorm activity in the tropical cyclone away from the low pressure center and thunderstorms provide energy to fuel the tropical cyclone, high shear would disrupt the supply of energy needed to fuel intensification.
Lastly, the tropical cyclone needs instability and moisture. Instability is important because thunderstorms are necessary for tropical cyclone intensification and need moist air near the surface in order to develop. When the atmosphere is unstable, it is typically warm, moist, and prone to rising. As more warm and moist air rises, more thunderstorms develop. A moist atmosphere is necessary to keep fueling the storm with warm water. Dry air wrapping into the tropical cyclone can cut off the moisture needed for development, breaking up the core circulation and disrupting the organizational structure.
When these necessary conditions are all in play, the environment is favorable for the development of a tropical cyclone, which can then intensify into a possible hurricane. As we head into the beginning of August, tropical cyclone activity will be on the rise, and if a tropical cyclone develops within the Atlantic we’ll be tracking it.
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