Contrary to how many weather maps appear, a hurricane is more than a point on a weather map, and its path is more than a line. It is a large system that can affect a wide area, requiring that precautions be taken far from where the eye is predicted to come ashore.
There are three main parts of a tropical cyclone or hurricane:
- Eye – This is the center. It is the calm part of the storm.
- Eye Wall – This part is around the eye. This part has the strongest winds and rains. The winds may blow 200 miles per hour.
- Rain Bands – These are the clouds that spin out and make the storm bigger.
Air spirals in toward the center in a counter-clockwise pattern in the northern hemisphere (clockwise in the southern hemisphere), and out the top in the opposite direction. The following are the parts of a tropical cyclone:
The hurricane's center is a relatively calm, generally clear area of sinking air and light winds that usually do not exceed 15 mph (24 km/h) and is typically 20-40 miles (32-64 km) across. An eye will usually develop when the maximum sustained wind speeds go above 74 mph (119 km/h) and is the calmest part of the storm.
Around 74 mph (119 km/h) the strong rotation of air around the cyclone balances inflow to the center, causing air to ascend about 10-20 miles (16-32 km) from the center forming the eyewall. This strong rotation also creates a vacuum of air at the center, causing some of the air flowing out the top of the eyewall to turn inward and sink to replace the loss of air mass near the center. This sinking air suppresses cloud formation, creating a pocket of generally clear air in the center.
Where the strong wind gets as close as it can is the eyewall. The eyewall consists of a ring of tall thunderstorms that produce heavy rains and usually the strongest winds. Changes in the structure of the eye and eyewall can cause changes in the wind speed, which is an indicator of the storm's intensity. The eye can grow or shrink in size, and double (concentric) eyewalls can form.
Curved bands of clouds and thunderstorms that trail away from the eye wall in a spiral fashion. These bands are capable of producing heavy bursts of rain and wind, as well as tornadoes. There are sometimes gaps in between spiral rain bands where no rain or wind is found.
- NOAA – NWS – JetStream – Online School for Weather – Tropical Cyclone Structure: http://www.srh.noaa.gov/jetstream/tropics/tc_structure.htm
- Image Source: http://www.srh.noaa.gov/jetstream/tropics/tc_structure.htm [Accessed March 12, 2014]