Wind is measured in both sustained wind speeds, and 3-second gusts. When you see a weather report that gives "Winds out of the southwest at 25 mph with gusts of up to 40 mph", the 25 mph is the sustained wind speed, and the 40 mph velocity is a measured 3-second gust. Both 3-second gust wind speeds and sustained wind speeds are used as input variables for building construction codes, especially southern coastlines, where buildings have to withstand hurricanes.
Get the 3-second gust speed from the National Weather Service, by going to their website and entering your zip code. The forecast will show up on the website, and if winds of greater than 20 mph are predicted, the gust speeds will also be presented. In a weather emergency, the gust and sustained wind speeds are broadcast on emergency radio.
Subtract 20 if the 3-second gust is greater than 90 mph.
Subtract 15 from the result if the 3-second gust is 90 mph or less.
After going through either step 2 or 3, you will have the basic wind speed. This is used for determining if the building you're constructing (or currently inside of) can be expected to survive the wind you're experiencing without major structural damage. The National Weather Service provides guidance on basic wind speeds and degrees of hurricane proofing for a structure.