Effective on May 15, 2012, the US National Oceanic and Atmospheric Administration (NOAA) is making a modification to the Saffir-Simpson Hurricane Wind Scale, which is being used as a standard to measure hurricane intensity. The change broadens the Category 4 wind speed range by one mile per hour (mph) at each end of the range, yielding a new range of 130-156 mph.
The press release noted that "The National Hurricane Center (NHC) and Central Pacific Hurricane (CPHC) assign intensities of hurricanes in 5-knot (kt) increments. For advisory products, these intensities are converted to miles per hour (mph) and kilometers per hour (km/h), and then rounded to the nearest 5-mph or 5-km/h increments. Challenges occur when the current Category 4 intensity is 115 kt (132.3 mph). Although 115 kt is within the Category 4 range, the equivalent rounded wind speed in mph is 130 mph, which is in the Category 3 range. To classify the hurricane as a Category 4 in both sets of units (kt and mph), NHC and CPHC must incorrectly convert 115 kt to 135 mph in the advisory products. A similar issue occurs when the current Category 4 intensity of 135 kt is converted to km/h."