How hurricanes are measured

Published 12:00 am Tuesday, September 20, 2005

Over the past few weeks this column has examined various aspects of hurricanes and their application to recreational boating, safety issues, insurance concerns and even what to do if caught up in one while underway.

I have to tell you the reaction has been wonderful; lots of nice e-mails from boaters as far away as Washington state who have read the column (I didn’t know the News-Herald had a following in Silverdale Washington… the Internet makes all sorts of things possible!). It looks like I have hit a key issue, and with Katrina and Ophelia on everyone’s minds the topic continues to be a natural.

A recent visit to the U.S. Coast Guard’s Storm Center Web site – provided yet another good area when discussing hurricanes. If you have not taken the time to visit this well-designed site, you should take a minute and look in. There is lots of good useful information which is easy to navigate. After flipping through the site I decide I’d focus on the Saffir-Simpson Scale.

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Throughout last week Ophelia switched between a Category One Hurricane and a Tropical Storm. From local television weather forecasters, to the Weather Channel, to the discussions revolved around the storm’s unique track, which included several &uot;stalls&uot; to an intensification last Wednesday evening in which the Hurricane Hunter Aircraft recorded 90 mph winds.

The National Weather Service’s National Hurricane Center ( provides the best explanation of this scale and what each means. The premise is actually quite easy to understand. Saffir-Simpson uses a 1-5 scale to provide a description of the storm’s intensity. This information is used to judge the potential for damage. The key factor is the speed of the wind. Saffir-Simpson also provides key decision makers information on possible storm surge, which can be a real issue for everyone.

I found it interesting this past week, while watching the Weather Channel, the cavalier attitude that many had while being interviewed by the reporters. They shrugged off a Category One hurricane as if it was a light rainstorm. That can be an incredibly big mistake. A hurricane is a powerful storm that you do not want to mess with. Regardless of your location &uot;even&uot; a category one can cause significant damage to boats that may be pierside or an anchor.

Here is what the Coast Guard Storm Center Web Site provides via a link to the National Hurricane Center site reprinted less the examples of specific hurricanes for brevity sake:

Category One Hurricane:

Winds 74-95 mph (64-82 kt or 119-153 km/hr). Storm surge generally 4-5 ft above normal. No real damage to building structures. Damage primarily to unanchored mobile homes, shrubbery, and trees. Some damage to poorly constructed signs. Also, some coastal road flooding and minor pier damage.

Category Two Hurricane:

Winds 96-110 mph (83-95 kt or 154-177 km/hr). Storm surge generally 6-8 feet above normal. Some roofing material, door, and window damage of buildings. Considerable damage to shrubbery and trees with some trees blown down. Considerable damage to mobile homes, poorly constructed signs, and piers. Coastal and low-lying escape routes flood 2-4 hours before arrival of the hurricane center. Small craft in unprotected anchorages break moorings.

Category Three Hurricane:

Winds 111-130 mph (96-113 kt or 178-209 km/hr). Storm surge generally 9-12 ft above normal. Some structural damage to small residences and utility buildings with a minor amount of curtainwall failures. Damage to shrubbery and trees with foliage blown off trees and large trees blown down. Mobile homes and poorly constructed signs are destroyed. Low-lying escape routes are cut by rising water 3-5 hours before arrival of the center of the hurricane. Flooding near the coast destroys smaller structures with larger structures damaged by battering from floating debris.

Category Four Hurricane:

Winds 131-155 mph (114-135 kt or 210-249 km/hr). Storm surge generally 13-18 ft above normal. More extensive curtainwall failures with some complete roof structure failures on small residences. Shrubs, trees, and all signs are blown down. Complete destruction of mobile homes. Extensive damage to doors and windows. Low-lying escape routes may be cut by rising water 3-5 hours before arrival of the center of the hurricane. Major damage to lower floors of structures near the shore. Terrain lower than 10 ft above sea level may be flooded requiring massive evacuation of residential areas as far inland as 6 miles (10 km).

Category Five Hurricane:

Winds greater than 155 mph (135 kt or 249 km/hr). Storm surge generally greater than 18 ft above normal. Complete roof failure on many residences and industrial buildings. Some complete building failures with small utility buildings blown over or away. All shrubs, trees, and signs blown down. Complete destruction of mobile homes. Severe and extensive window and door damage. Low-lying escape routes are cut by rising water 3-5 hours before arrival of the center of the hurricane. Major damage to lower floors of all structures located less than 15 ft above sea level and within 500 yards of the shoreline. Massive evacuation of residential areas on low ground within 5-10 miles (8-16 km) of the shoreline may be required.&uot;

The National Hurricane Center makes it easy to understand the scale and what it means when forecasters state that we have a Category Two hurricane inbound. Bottom line – don’t take any storm lightly especially &uot;just&uot; a Category One.

Until next week…boat safe…boat smart and remember the brave men and women that are engaged in the recovery efforts in the wake of Hurricane Katrina. They are sacrificing so that a great part of this country can rebuild – even better than before.

Joe DiRenzo III is a retired Coast Guard Officer and former cutter Commanding Officer. Currently a Coast Guard civilian employee, he is a nationally recognized expert on port security and maritime terrorism issues. He has written boating columns for the Suffolk News-Herald for just under five years.