The hearts of many a coastal dweller stop when they hear the word “hurricane.” These large, brutal, all-too-common weather events are often misunderstood, however. Just what are these awesome engines of destruction?
--Tropical Cyclones--
A hurricane is not actually a weather system itself, but a strength classification--it is the strongest form of a weather phenomenon known as a tropical cyclone. Tropical cyclones are large low-pressure systems built from heat, moisture, and winds, that form over warm oceans. They are easily identifiable in radar images because of their cyclonic (that is, rotating) structure and distinctive central “eye.”
Though the full processes that create a tropical cyclone are not fully understood, they generally form in the presence of rising heat and falling condensation caused by warm, churning waters and localized thunderstorms or similar weather. The cycle of rising heat and falling water creates winds, which are spun by a phenomenon known as the Coriolis Force, which in turn speeds up the cycle of heat and condensation, speeding up the winds, speeding up the spin, etc. The result is a storm of often devastating proportions.
These tropical cyclones are unique because they require moisture to set the process into motion; land-based cyclones, such as the common tornado, are solely the result of temperature gradients. This difference allows tropical cyclones to grow much larger and more stable than land-based cyclones, making them far more dangerous.
Tropical cyclones are just that: tropical. They can form only in warmer climates, and no tropical cyclone has ever formed more than 30 degrees from the equator. Furthermore, meteorologists have identified seven distinct “basins” where tropical cyclones typically form, thereby making prediction (and more importantly, early warning) easier.
--Classification--
Once meteorologists identify a tropical cyclone, they categorize it by measuring its surface winds. Systems with maximum sustained surface winds of 39mph are called tropical depressions. When sustained winds rise to between 39 and 73 mph, it is called a tropical storm. And when sustained winds reach 74 mph or more, the storm becomes a _hurricane_.
Once a storm reaches hurricane proportions, it is further categorized (via a measurement known as the Saffir-Simpson Scale) into a power category. The least powerful, Category 1, features sustained winds of under 100 mph, while the most powerful and rare, the Category 5 storms, reach sustained wind speeds of 150 mph or more.
“Hurricane” is only one designation for powerful tropical cyclones, used mainly in the Americas and Europe. In the western Pacific the storm is commonly called a “typhoon,” a “severe cyclonic storm,” or simply a “severe tropical cyclone.” No matter what the name, however, the destructive power of these storms remains the same.
--Landfall--
Hurricanes are feared because, upon reaching land, they bring terrible devastation. In addition to high sustained winds and severe thunderstorms, a hurricane’s movement across the water creates storm surges and tides that flood the coasts. Once it reaches land it can generate embedded tornadoes that wreak further destruction. Even lower-category hurricanes can damage foliage, signage, and unanchored property, while also flooding low-lying areas. The more powerful storms can flood, damage, or destroy entire neighborhoods; they deteriorate beachfronts, shatter windows, and even ruin whole structures with their fury. In addition to the property damage, landfall can take lives and force millions to flee inland. At every level, the cost of a hurricane’s landfall is high.
North America sees at least one major hurricane landfall each year. Amongst the more infamous in history is Agnes, a Category 1 storm that stands out for its longevity; it made landfall not just once, but twice, striking both Florida and New York City before it subsided, causing $3 billion in damages and killing 122 people. Hugo, a Category 4 hurricane that struck the Carolinas in 1989, caused $7 billion in damage and took some 50 lives. In 1992, Hugo was outmatched by hurricane Andrew, which caused a massive $23 billion in damage to Florida and Louisiana and took 23 lives.
More recently, 2004 saw not one, but four devastating hurricanes hit Florida and the surrounding coasts. The season began with Charley, a Category 3 Storm that stuck in August. Charley was followed three weeks later by Frances, a Category 4 storm, and Ivan, a long-sustaining storm that went from Category 3 to 5 and then back to 3. In late September, Jeanne, a Category 3 storm, also devastated Florida and the surrounding coasts. Between them, the four storms caused over $100 billion in damages and more than 100 deaths.
--Names--
Finally, you may wonder what’s up with the names that we give tropical storms and hurricanes. Every few years, the World Meteorological Organization generates alphabetical lists of names to help record and track any tropical cyclone that reaches tropical storm status. The names vary from year to year, and are given out alphabetically, starting each year with “A.” When a name is given to a particularly destructive storm, the name is retired afterwards; it will never again appear on the WMO’s list.
