We have talked a lot about the National Hurricane Center’s (NHC) track forecasts and the associated uncertainty in the track forecasts. We should also understand the uncertainties associated with intensity forecasts.
The first step is to understand what the NHC means when it refers to the maximum sustained wind in tropical cyclone advisories. The wind is defined as the 1-minute average wind at the 10-meter elevation. The National Hurricane Operations Plan says “Maximum 1-Min Sustained Surface Wind. When applied to a particular weather system, refers to the highest 1-minute average wind (at an elevation of 10 meters with an unobstructed exposure) associated with that weather system at a particular point in time.”
It is this maximum sustained wind that the NHC uses to determine a tropical depression (maximum sustained winds 38 mph or less), tropical storm (maximum sustained winds 39 to 73 mph) and hurricane (maximum sustained winds 74 mph or greater).
That sounds simple, but in practice the maximum sustained winds of a tropical cyclone cannot be measured exactly for one minute at exactly 10 meters throughout the life of the tropical cyclone. Most of the time, the maximum sustained wind is estimated. More on that later.