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Hurricanes are only one type of tropical cyclone. Tropical cyclones are warm-core, low pressure systems without any "front" attached, that develop over the tropical or subtropical waters, and have an organized circulation. Depending upon location, tropical cyclones have different names around the world. In the:

  • Atlantic and Eastern Pacific they are called hurricanes.
  • Western Pacific they are called typhoons.
  • Indian Ocean they are called cyclones.

Before and after images of Rockaway NY showing the damage caused by Hurricane Sandy.
Aerial photos of Hurricane Sandy damage
Members of the public can now get a birds-eye view of some of the destruction caused by Hurricane Sandy...

Regardless of what they are called, tropical cyclones are powered by heat from the sea. They are products of a warm tropical ocean and a warm, moist atmosphere. Hurricanes are typically steered by easterly winds, generally south of 25° north latitude and by high-level westerly winds north of 25° north latitude. There are several favorable environmental conditions that must be in place before a tropical cyclone can form. They are:

  • Warm ocean waters (at least 80°F / 27°C) throughout a depth of about 150 ft. (46 m).
  • An atmosphere which cools fast enough with height such that it is potentially unstable to moist convection.
  • Relatively moist air near the mid-level of the troposphere (16,000 ft/4,900 m).
  • Generally a minimum distance of at least 300 miles (480 km) from the equator.
  • A pre-existing near-surface disturbance.
  • Low values (less than about 23 mph/37 kph) of vertical wind shear between the surface and the upper troposphere. Vertical wind shear is the change in wind speed with height.

This image uses the model output from the ECMWF experiment, showing where Sandy was predicted to be located five-days out with the normal satellite data inputs into the model. Without the polar-orbiting satellite data, Sandy stays out to sea and appears more organized, illustrating the necessity of polar-orbiting satellite data for model predictions.
Polar-orbiting satellite pinpoints Sandy's track
Forecasts of Hurricane Sandy's track could have been hundreds of miles off without information from polar-orbiting satellites..

Storm surge

Although hurricanes are well known for their strong and destructive winds, a hurricane’s storm surge is by far the greatest threat to life and property along the immediate coast. Storm surge is simply water that is pushed toward the shore by the force of the winds swirling around the storm. This advancing surge combines with the normal tides to create the hurricane storm tide, which can increase the mean water level 15 feet or more. In addition, wind driven waves are superimposed on the storm tide. This rise in water level can cause severe flooding in coastal areas, particularly when the storm tide coincides with the normal high tides. Because much of the United States' densely populated Atlantic and Gulf Coast coastlines lie less than 10 feet above mean sea level, the danger from storm surges is tremendous.

NOAA hurricane hunter WP-3D Orion and Gulfstream IV aircraft in flight.
Destination: The storm's eye
Despite the dangers, NOAA's Hurricane Hunters fly directly into storms in sensor-packed planes to gather data...

EDUCATION CONNECTION

As the climate changes and the strength and paths of hurricanes also change, it is increasingly important for students to understand hurricanes. This collection provides educators and students with resources to explore how hurricanes form, their potential effects to humans and ecosystems, ways to prepare for hurricanes, and even a citizen science project to classify hurricanes from satellite imagery.

Adapted from NOAA Jetstream, Storm Surge, and Hurricanes… Unleashing Natures Fury

Page last updated: June 2015.