How do Hurricanes Form?

Ingredients for Hurricane Formation

How do hurricanes form? Hurricanes usually form in the summer or early autumn when several key atmospheric ingredients come together. Contrary to common belief, many factors other than warm ocean water cause hurricanes to form. In fact, the water is always warm enough in the deep tropics for hurricanes to form all year long. During the winter and spring, upper air winds are hostile, and usually do not allow tropical cyclone development. So, what does it take for a hurricane to form?

  • 1. Pre-existing Disturbance or low pressure area must have formed in the low levels of the atmosphere to start winds converging and uplift.
  • 2. Warm Water to a sufficient depth to support the energy that a hurricane will need. The temperature needs to be about 26.5º Celsius or 80º Fahrenheit to a depth of about 50 meters or 150 feet deep.
  • 3. Low Stability will allow deep convection or cumulonimbus clouds to build to great heights in the atmosphere. A stable air mass will inhibit cloud development and not allow for significant cloud growth to support the deep convection needed for a hurricane to develop.
  • 4. Coriolis Force The disturbed area of weather needs to be at least 4-5º away from the equator. This is the approximate distance from the equator for the Coriolis force to achieve a gradient wind balance to sustain the low pressure area.
  • 5. Moist Mid Level of the atmosphere. If there is dry air aloft it will weaken or choke off the updrafts in the cumulus clouds.
  • 6. Low Vertical Wind Shear from the surface to upper troposphere. This allows for the thunderstorm clouds to build to great heights. If the wind speed increases or changes direction with height, the cumulonimbus clouds get deformed can not sustain the hurricane heat engine.
  • 7. Divergence in the upper Atmosphere allows for the transport of mass away from the hurricane.

Hurricane Formation

If the conditions above are met sufficiently, showers and storms will start to gain organization as low level winds converge toward the center of the low pressure area. The cluster of convection will start to form bands. As the convection increases, the warm air near the surface rises and cools. As it cools the water vapor condenses. There is a tremendous amount of heat produced from the condensation of water vapor. Some of this heat warms the center region of the low. As the temperature of the air near the core rises it produces lower pressure. In response to this lower pressure, winds increase in intensity. A tropical storm forms when the surface winds reach sustained winds of 39-73 mph. A hurricane officially classified as the winds reach sustained values of 74 mph.

Even if all of the ingredients of a hurricane are in place, it does not guarantee that a hurricane will form. Many of the factors in hurricane formation exist in the tropics, especially in the heart of hurricane season. Despite this, very few disturbances actually develop into a hurricane.

Remember, regardless of how hurricanes form, they can pose problems while traveling to tropical vacation locations. It you are visiting Florida, the Caribbean, Mexico on your favorite cruise line, check our travel resources to help make your trip the best!

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