Hurricane Season: A Primer

The ingredients for a hurricane include a pre-existing weather disturbance, warm tropical oceans, moisture, and relatively light winds aloft.

How do hurricanes form? (Credit: weatherwizkids.com)

How do hurricanes form? (Credit: weatherwizkids.com)

If the right conditions persist long enough, they can combine to produce the violent winds, incredible waves, torrential rains, storm surges, and floods we associate with this phenomenon.

For a hurricane to form, the ocean water must be warmer than 81degrees. The heat and moisture from this warm water is ultimately the source of energy for hurricanes.

Hurricanes evolve through a life cycle of stages from birth to death. A tropical disturbance in time can grow to a more intense stage by attaining a sustained wind speed of 74 mph. Hurricanes can often live for a long period of time—as much as two to three weeks. They may initiate as a cluster of thunderstorms over the tropical ocean waters.

Once a disturbance has become a tropical depression, the amount of time it takes to achieve the next stage, tropical storm, can take as little as half a day to as much as a couple of days. It may not happen at all. The same may occur for the amount of time a tropical storm needs to intensify into a hurricane. Atmospheric and oceanic conditions play major roles in determining these events.

Hurricanes are huge, really enormous in size. The average hurricane is 200-400 miles across. Big ones will be 550-plus miles.

The relative strength of a hurricane is measured on a scale based on its greatest wind speed. This scale is named the Saffir-Simpson Scale for the men who invented it. This scale ranges from categories 1 to 5, with category 1 hurricanes being the weakest, and 5s the most intense. Hurricanes strong enough to be considered intense start at category 3 or with sustained winds exceeding 111 mph.

This photo is a composite of three days' views (Aug. 23, 24, and 25, 1992) of Hurricane Andrew as it slowly moved across south Florida from east to west. (Credit: NASA)

This photo is a composite of three days’ views (Aug. 23, 24, and 25, 1992) of Hurricane Andrew as it slowly moved across south Florida from east to west. (Credit: NASA)

There have only been two category 5 hurricanes that made landfall on the mainland U.S. (Florida Keys 1935 and Camille 1969). Recent intense hurricanes to make landfall on the United States were Opal in 1995 and Fran in 1996.

On average ten tropical storms develop over the Atlantic Ocean, Caribbean Sea, and Gulf of Mexico each storm season. Many of these remain over the ocean. Six of these storms become hurricanes each year.

In an average three-year period, roughly five hurricanes strike the United States coastline, killing approximately 50 to 100 people anywhere from Texas to Maine. Of these, two are typically “major” or “intense” hurricanes, with winds greater than 110 mph.

Researchers continue to investigate possible interactions between hurricane frequency and El Niño. El Niño is a phenomenon where ocean surface temperatures become warmer than normal in the equatorial Pacific. In general, warm El Niño events are characterized by more tropical storms and hurricanes in the eastern Pacific and a decrease in the Atlantic, Gulf of Mexico, and the Caribbean Sea.

Under the right atmospheric conditions, hurricanes can sustain themselves for as long as a couple of weeks. Upon reaching cooler water or land, hurricanes rapidly lose intensity.

Hurricanes don’t occur suddenly, like in the movies. It takes days and weeks for hurricanes to build from tropical depression, to tropical storm, and finally to hurricane. There is plenty of warning before a hurricane hits.

Hurricanes normally travel slowly averaging 10-20 miles an hour, though on rare occasions they can move along as fast as 70 mph or creep along at two or three.

Hurricanes do not travel in straight lines. They take curving paths, often looping and backtracking, and zig-zagging.

Hurricanes can have tremendous amounts of rain or very little.

Hurricanes have an eye, the center of the storm. The eye can be from five to 120 miles across with most being 20-40. The eye can be eerily calm with clear skies, fooling people into thinking the storm is over. However, once the eye passes over, the other half of the storm is still left to endure, with sudden ferocious winds coming from the opposite direction.

Threat Map for Hurricane season 2013 (Source: firstchoiceweather.com)

Threat Map for Hurricane season 2013 (Source: firstchoiceweather.com)

The sustained winds of a hurricane (74 to over 190 mph) are destructive and cause severe damage. However, hurricanes often spawn numerous tornadoes which also cause much of the damage. Flying debris can be a bigger hazard than the wind itself.

Hurricanes are tropical in nature but are not restricted to tropical areas, the coast, or the summer. Some of the worst and most damaging hurricanes have hit the Carolinas and northward in September.

The majority of hurricanes occur during late August and September.

Note: This is Part 3 of a 4-part series on Hurricanes and the RVer

Part 1: Hurricane Primer for RVers

Part 2: Are You Prepared for This Year’s Hurricane Season?

Part 4: The One-Eyed Monster: Storm Surge & Saffir-Simpson Scale

Worth Pondering…

Two things Florida can teach the other 49 states: how to make a good margarita and how to deal with the aftermath of a hurricane.
—Tom Feeney

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