Scale that categorizes hurricanes was tweaked this year

Hurricane Katrina was categorized a strong category 3 hurricane on the Saffir-Simpson scale when it made landfall in 2005.

By Sonya

CHARLESTON, S.C. (WCIV) -- Hurricanes are classified into various categories using the Saffir-Simpson scale.

The strength of the sustained winds determines whether the storm is a Category 1,2,3,4, or 5.

The scale has been used since 1971, but this year slight modifications were made.

The wind speed range for Category 1 and 2 hurricanes remains the same. A Category 3 hurricane now has winds from 111 mph to 129 mph, instead of 130. A Category 4 storm previously had sustained winds from 130 to 155 mph, but now the range is up to 156. A Category 5 storm now has winds of 157 mph or higher instead of the previous 156 mph.

The reason for the change was so the hurricanes will remain in the correct category, whether the wind speed is measured in knots or miles per hour. Essentially, it will make the conversion between the two units much easier for meteorologists.

And there is another change that has come along this year too There is a new model that will predict the start of the developing eyewall replacement cycle.

The eyewall is the organized band of clouds that immediately surround the eye, or the center, of a hurricane. It is where the most intense winds and rainfall occur.

The eyewall replacement cycle occurs when a second eyewall forms around the original and eventually overtakes it. This especially happens in strong, long-lived hurricanes.

The new model will predict this eyewall replacement cycle by measuring parts of the storm's structure and environment and relating them to the conditions observed during past replacement cycles.

The hope is that this model will eventually help to improve intensity forecasts in the future. This project is part of the NOAA Joint Hurricane Testbed.