The Fujita scale was developed in the 1970s to classify the intensity of tornadoes. It is a subjective scale, as winds in a tornado are often not directly measured -- and it is not very safe to do so accurately, and very hard to do it accurately while staying safe! -- and are instead estimated based upon observed damage. It is a scale that bridges the gap between the Beaufort scale (mostly used by mariners for classifying wind speeds) with F1 starting at Beaufort 12 and the Mach scale, with F12 equal to Mach 1 (or 738mph). However, there have been no tornadoes definitively above F5 in recorded history.

The Saffir-Simpson scale was developed in 1969 as a means of classifying hurricane damage based upon intensity for a WMO project. The categories were developed by the then-director of the NHC, Dr. Simpson, along with Herbert Saffir, an engineer, and the speeds were assigned based upon breaks in observed damage. This contrasts with the Fujita scale, where the speeds were spread apart to bridge the Beaufort and Mach scales. Obviously, as most people know the Saffir-Simpson scale, a complete treatise on the subject is rather unnecessary. The NHC has a good reference on the types of storms by category (damage, surge, and other characteristics) on their webpage.