Five Facts About Irene and Her Ilk.

Our weekday column, 5 Things You Need to Know, provides you with information that can help you plan your day and give you some fodder for water cooler conversations. The following facts are based on information from the National Hurricane Center:

1. What is a hurricane, exactly? It is a low pressure system, a form of cyclone, that forms in the tropics. It is accompanied by thunderstorms and in the northern hemisphere, counterclockwise circulation of winds.

2. How fast do the winds circulate? To be classified as a hurricane, as opposed to the less several tropical storm or tropical depression, the winds have to have a sustained maximum of 74 mph, or higher.

3. How are hurricanes ranked? Hurricanes are categorized from 1 to 5 in strength, using the Saffir-Simpson wind scale. The most powerful — Category 5 — has sustained winds of more than 155 mph, and will cause catastrophic damage.

4. What is catastrophic damage? Here are a few sentences from the National Hurricane Center description: "People, livestock, and pets are at very high risk of injury or death from flying or falling debris, even if indoors in mobile homes or framed homes. Almost complete destruction of all mobile homes will occur, regardless of age or construction."

5. What was the deadliest hurricane in U.S. history? The deadliest was in 1900, when a Category 4 storm struck Galveston, TX, killing 8,000 to 12,000 people.