The Three Phases of Hurricane Development

The NOAA (National Oceanic and Atmospheric Administration,) tells us that hurricanes are the most severe of meteorological phenomena. They are essentially tropical cyclones that form from low pressure systems that rotate in a counter clockwise motion. They are accompanied by thunderstorms. But before a tropical cyclone actually becomes a hurricane, it goes through several stages of development. Although the full blown hurricane is the most dangerous, no one should take a developing storm in any phase lightly because of the potential for damage or loss of life.

*Tropical Depression –

A tropical depression is comprised of a well organized system of clouds and thunderstorms. There is also a well defined surface circulation of the wind whose maximum sustained speed is 38 mph or less.

*Tropical Storm –

A tropical storm is essentially the same thing as a tropical depression, except that sustained wind speeds can range between 39 and 73 mph.

*Hurricane –

A hurricane is much more intense than the previous types of tropical cyclones. It is a tropical weather system consisting of thunderstorms and a well defined surface circulation. The maximum sustained speeds must exceed 74 mph for a storm to be classified as a hurricane

♣ Stages of development  –

• Birth of a Tropical Cyclone –

These storms form over warm waters, and they develop out of some type of preexisting disturbance. It is typical for these disturbances to emerge from the African coast approximately every 3 to 4 days (between June 1 and November 30, the time period of the hurricane season.) They begin as tropical waves that come from areas of unsettled weather. It is also possible for a tropical cyclone to be formed from the trailing end of a cold front, or from an upper level low system.

Three conditions are necessary for the formation and development of a tropical cyclone and its subsequent strengthening and development into a hurricane.

1.) A preexisting disturbance that also contains thunderstorms.

2.) Warm ocean temperatures that are at least 80 degrees from the surface to a depth of 150 feet.

3.) There must be light upper level winds whose speed and direction have little to no change throughout the depth of the atmosphere. and this results in low wind sheer.

• Growth and Maturity –

Before the storm begins to strengthen, which it can only do if the conditions are favorable, the system may appear on satellite images as little more than an unorganized cluster of thunderstorms. As long as sustained winds don’t exceed 38 mph, the storm will remain a tropical depression, but it will still acquire the hurricane-like spiral appearance because of the earth’s rotation and the flow of winds.

As the storm continues to strengthen, it becomes a tropical storm with sustained winds of anywhere between 39 and 73 mph. Thunderstorm bands will provide the added heat and moisture to fuel the storm’s development.

At the point when the storm reaches sustained wind speeds of 74 mph or greater, it is officially classified as a hurricane. Air at the center of the storm sinks rapidly, drying and warming the area. This cloud free area is the eye of the storm.

People often fail to realize that a storm is imminent because the eye makes landfall before the most intense part of the storm. They sometimes even mistakenly believe that they aren’t going to be hit by the most intense part of the storm because the eye makes landfall at a specific place before the most intense parts of the storm set in. A hurricane can have a life span of more than two weeks while it is in the ocean. It can also potentially travel up the entire Atlantic coast.

• End of the storm –

Many factors can contribute to the demise of a hurricane, just as many factors contribute to its birth. There are also many reasons for which a hurricane may eventually decay and those reasons can include:

1.) The hurricane may be torn apart by wind sheer.

2.) It can weaken after moving over cooler and dryer areas.

3.) The main source of a hurricane’s moisture is the ocean, but that is cut off when the storm makes landfall.

4.) When the storm passes over land, friction may cause a reduction in the surface circulation.

Weakening hurricanes can easily strengthen if they move into a better area or interact with a mid-latitude frontal system. Additionally, hurricanes have been known to regain strength if they travel again into open waters. For this reason, people can easily be fooled into thinking that there is no longer any danger if a hurricane struck elsewhere.

The Gulf of Mexico is an especially ripe area for hurricane development and strengthening because the waters are warm there. The area known as the Loop Current is especially conducive to the development or strengthening of hurricanes because, unlike other areas of the Gulf or the Caribbean Sea, the water remains warm to much greater depths. With the Deep Water Horizon oil rig catastrophe and subsequent major oil leak, there is no telling what might happen if a hurricane were to develop or strengthen in the waters of the Gulf of Mexico, especially in Loop Current Area.


NOAA Hurricane Handbook –