04.21.12

Saffir-Simpson Scale Gets Tweaked

Posted in Storm Facts, Hurricane Intensity at 5:00 pm by gmachos

Scale That Measures Hurricane Intensity Gets Minor Change For Category 4 Storms

Another loose end that was cleared up going into the 2012 Atlantic Hurricane Season was a minor adjustment done to the Saffir-Simpson Scale.  To clear up an issue with wind speeds for Category Four Hurricanes, the National Hurricane Center made an adjustment to the scale that measures hurricane intensity.  Now, Category Three Hurricanes will have winds from 111 to 129 miles per hour, Category Four storms will have winds from 130 to 156 miles per hour, and Category Five systems will have winds greater than 157 miles per hour.

The reason why this is occurring is because of a conversion issue with the wind speeds.  Maximum sustained winds measured in tropical storms and hurricanes are measured in knots, which are converted to miles per hour.  Currently, 115 knots is equivalent to 132.3 miles per hour.  When the wind speeds are converted from knots to miles per hour, they are rounded off usually.  In this case, 115 knots would be equivalent 130 miles per hour.  However, 115 knots, which has been within the current threshold for Category Four storms, usually is rounded up to 135 miles per hour. 

The same problem occurs with Category Four to Category Five hurricanes.  As a result, the scale has been tweaked to reflect the reduction of the wind speed interval in Category Three from 111 to 129 miles per hour, and Category Five now being set to 157 miles per hour or greater.  Now, the scale accurately reflects the wind speeds for Category Four systems.  The changes will become effective at the start of the 2012 Eastern Pacific Hurricane Season, which begins on May 15, and will also go into effect for the upcoming Atlantic season.

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