GIS and Hurricanes
Take Away
Seealso the ESRI Education Document on Hurricanes and the ArcExplorer Document
What is a Hurricane?
A hurricane is an intense, rotating oceanic weather system that possesses maximum sustained winds exceeding 119 km/hr (74 mph). It forms and intensifies over tropical oceanic regions.
Hurricanes are generally smaller than storms in mid-latitudes, typically about 500 km (311 miles) in diameter. At the ocean’s surface, the air spirals inward in a counterclockwise direction. This cyclonic circulation becomes weaker with height, eventually turning into clockwise (anticyclonic) outflow near the top of the storm.
How Does A
Hurricane Form?
How does a hurricane form? Do they just form when Mother Nature gets angry? No they don’t, hurricanes form in tropical regions. They form there because they need warm water of at least 80º Fahrenheit, high humidity with moist air, light winds, and very warm surface temperatures. Summer and the early fall months are perfect for hurricanes to brew up in the oceans around us. Most of the Atlantic hurricanes brew up on the coast of Africa. For that the northern hemisphere hurricane season is considered through the months of June and November.
The first sign of a hurricane is a cluster of thunderstorms over tropical oceans. After the cluster of thunderstorms arrives they will break away and become better organized. It can take anywhere from hours to several days for a thunderstorm to actually turn into a hurricane. Three things must happen for a hurricane to form though. A continuous evaporation and condensation cycle must take place, patterns of winds that are characterized by the converging winds, and a difference in air pressure between the surface and high altitude.
Warm and moist air from the ocean will begin to rise at rapid rates. As this warm air rises the water vapor condenses to form dark storm clouds and droplets of rain. Surfaces pressures begin to decrease as water vapor condenses and releases latent heat into areas where the tropical disturbance is located. (Latent heat is heat energy that is released during the phase change of water vapor.) This latent heat causes the air to become less dense. The warm air then rises; as it rises it becomes cooler and expands. That triggers more condensation and releases more latent heat, which allows more air to rise. A chain reaction is now in place. The exchange of the heat from the surface creates a pattern of wind that moves around the center.
Then converging winds—which are winds moving in different directions that run into each other—converging winds at the surface collide and then push warm air downward and the moist air upward. The rising air backs up the air that is already rising from the surface. So then, wind speeds of the storm increase. In the meantime, strong winds that are blowing at high speeds and at high altitudes help to remove the hot rising air from the storms center. But if there are wind shears (Wind shears are when directions of wind and speed differ.) the storm will weaken.
If there are aren’t any wind shears the storm’s air in the upper atmosphere will rise to higher and higher pressures. Therefore the air cycle and hurricanes growth will get bigger and bigger. There you have your hurricane.
Hurricanes
Some Additional Web Links
- NationalHurricaneCenter:
- Hurricane and Storm Tracking:
- Canadian Hurricane Centre:
- HurricaneTrack.com:
- Hurricane Tracking and Plotting:
- StormAdvisory:
- HurricaneResourceCenter:
- Stormpulse:
Satellite Images:
- Real Time Satellite Tracking:
David R. Green –