Tropical Cyclones: Storms by Any Other Name
Tropical cyclones are gigantic storms that occur in the tropics around the globe. In the Northern Hemisphere, the season for these storms is from June through November and the peak period is in August and September. In the Southern Hemisphere, storm season lasts from December through May with the peak period in February and March. Tropical storms have many names that vary from place to place.
In the northern Atlantic Ocean, in the Caribbean Sea, Gulf of Mexico or in the eastern Pacific, they are called hurricanes. In the West Indies, they are huracans. They are typhoons in the western North Pacific Ocean and in the China Sea; the word comes from tai-fung, Cantonese for great wind.
There are many other names for tropical cyclones, willy-willies in Northwest Australia and the Timor Sea, cyclones in the Indian Ocean, and baquiros in the Philippines, among many others, but they all describe the same thing, massive storms that threaten life wherever the occur.
All tropical storms begin life as unorganized clusters of thunderstorms that gradually begin to circulate in a cyclone manner. In the Northern Hemisphere, that is counterclockwise and in the Southern Hemisphere, that is clockwise. A few of these thunderstorm clusters intensify (warm water and instability are both essential to this) as they revolve around one another and a few organize enough to be called tropical disturbances. Even fewer grow into tropical storms and only a small percentage of the original thunderstorm clusters ever become the biggest storms of the tropics, a tropical cyclone.
Just how do they name these big storms? Names are assigned in annual lists years in advance and names are reused in 6-year cycles. The names are selected by countries in hurricane paths and are approved by regional hurricane committees of the World Meteorological Organization (there are several). Names are recycled every seventh year except for those of storms that caused extensive damage. Those storm names are not reused for at least 10 years and some are permanently retired from use, such as Camille.
Regardless of what they are called, all tropical cyclones have common traits. They are all born and evolve in the zone between the Tropic of Cancer and the Tropic of Capricorn, but not too close to the equator. The area within five degrees of latitude north and south of the equator is considered the ‘dead' zone, where tropical cyclones do not develop. Some professionals expand that area to include the zone within ten latitude degrees of the equator, but there have been storms that have proven exceptions to that rule.
All tropical cyclones are organized masses of convection with clearly evident cyclonic circulation. All have eye walls, which are rings of thunderstorms around the center of the storm. Some eye walls are very easy to see on satellite photos, others are not. All have strong winds and they all have their worst conditions in the northeastern quadrant of the storm relative to the direction of movement.
Speaking of bad conditions, tropical cyclones really produce them. The strong winds they pack create huge waves both out to sea and on the coasts. The winds alone have caused many ships to founder in an angry sea. Ships at sea are not the only things that are at risk.
When a tropical cyclone approaches land or makes landfall, millions of lives are endangered. A wall of water, called a storm surge, precedes landfall. Hurricane Camille pushed ashore a storm surge more than 25 feet above the normal tide line and effectively submerged Biloxi, Mississippi. Not much of the town remained after the storm had passed.
Enormous surf pounds coasts and can strip beaches of sand or completely wipe out barrier islands. Hog Island, a populated barrier island once off the southern coast of Long Island, New York, disappeared after a rare, intense hurricane crossed the region. Torrential rains with these massive storms cause flooding over an area hundreds of miles across. Tropical cyclones spawn tornadoes that race across the land, sometimes by the dozen, and wreak havoc wherever they touch ground.
Severe thunderstorms with hail, lightning, and powerful down rush gusts occur in masses. A tornado or severe thunderstorm may cost millions in lost lives and property, but a single tropical cyclone can kill thousands and cause billions of dollars worth of damage. More than 8,000 people died in the Galveston, Texas storm and a cyclone killed over 300,000 people in low-lying coastal areas of Bangladesh.
A tropical cyclone is a threat to humans that grows worse every year as coastal populations grow. As population density rises, evacuation is progressively more difficult and time-consuming. Without sufficient lead time ahead of a storm, complete evacuation is impossible, especially in big coastal cities like Miami, Charleston, and New York, and the required lead time gets longer and longer as cities grow. That’s where forecasters come into the picture. As weather science and technology advance, the tools forecasters use to make predictions improve and the stakes get higher all the time. Accurate, timely forecasting is a vital part of our defense against the monster storms known as tropical cyclones.
Written by Melody L. Higdon, 14 WS/DOPA