In April of 2010, the drilling rig Deepwater Horizon sank, leaving behind a gushing oil well that has caused the largest oil spill in US history. Now, with hurricane season already underway, many experts are concerned that hurricane conditions could further spread the oil over much of the southeastern US states. With hurricane Alex (which is currently forecast to hit Mexico) already causing disruptions in the form of 12-foot waves, it’s important that you understand the classifications for different types of hurricanes, as well as what kind of effect they can have when the pass over areas of land and water.
When Does a Tropical Storm Become a Hurricane?
The term “Tropical Cyclone” may refer to a hurricane, tropical storm, tropical depression, cyclone or cyclonic storm. It’s a general term for a weather system with a low-pressure center, as well as several strong thunderstorms. A tropical storm is measured at having sustained winds between 39 mph and 73 mph. When the winds inside a tropical cyclone reach a sustained speed of 74 mph (not including gusts), it is classified as a hurricane.
What is a ‘Storm Surge’?
For hurricane classifications, you will commonly see a reference to “storm surge height”. A storm surge is when the water level in an affected area goes up by a designated number of feet over sea level. This is caused mostly by the high winds of the storm system pressing down on the surface of the water. A storm surge is also sometimes casually referred to as a “storm tide”.
Saffir-Simpson Hurricane Scale
The Saffir-Simpson Hurricane Scale is the most widely known method for classifying hurricanes. The classifications are as follows:
Category 1 Hurricane:
This category occurs after a hurricane has formed from an existing weather system. The wind speeds of a Category 1 hurricane are from 74 – 95 mph. The storm surge is usually measured as being from 4 – 5 feet. Most of the damage from a Category 1 hurricane are to mobile homes, vegetation and some windows. Minor flooding in coastal areas.
Category 2 Hurricane
A category 2 hurricane has wind speeds from 96 – 110 mph. The storm surge may reach heights of from 6 – 8 feet. Damage to residential roofing, windows and doors is common. Mobile homes and shrubbery are under considerable threat. Any boat in an unprotected mooring is also at risk for serious damage.
Category 3 Hurricane
When a hurricane reaches category 3, its wind speeds have been measured at 111 – 130 mph. The storm surge may reach heights of from 9 – 12 feet. Residential structures are under considerable risk, and mobile homes are often completely destroyed. Serious flooding puts all coastal residential properties at additional threat. Minor number of curtainwall failures.
Category 4 Hurricane
A Category 4 hurricane has wind speeds from 131 – 155 mph, as well as storm surges that reach from 13 to 18 feet. Widespread curtainwall failures, as well as complete destruction of some small structures. Extensive beach erosion, and widespread flooding are also common.
Category 5 Hurricane
For a Category 5 hurricane, wind speeds are at or over 155 mph. The storm surge can reach over 18 feet. Hurricane Wilma (a 2005 storm) was the most intense Category 5 hurricane ever recorded in the Atlantic basin, with top wind speeds of over 185 mph. A hurricane of this strength could destroy many residential structures and cause severe flooding, which would result in large-scale evacuations.
Satellite Footage of Hurricane Dean (2007)
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