Hurricane Maria is in the news, following hard on the heels (literally and metaphorically) of Hurricane Irma. This has been upgraded and downgraded between Categories 4 and 5, which raises the question, what exactly are these categories.
From the National Hurricane Center's website it is simply the hurricane's sustained wind speed, in exactly the same way as the Beaufort scale, only much faster!
Category 1, 74-95 mph, Very dangerous winds will produce some damage
Category 2, 96-100 mph, Extremely dangerous winds will cause extensive damage
Category 3, 111-129 mph, Devastating damage will occur
Category 4, 130-156 mph, Catastrophic damage will occur
Category 5, 157 mph and above, Catastrophic damage will occur