Why the Saffir-Simpson Hurricane Intensity Scale had five levels we don’t know. The digits on a hand? Better than three, but lower resolution than the dozen rungs for wind speeds or earthquake intensity? Whatever the reason it seems to work.
In the late 1960s, Herbert Saffir, a Florida building engineer, was sent by the United Nations to study the hurricane vulnerability of low-cost housing in the Caribbean. He realized something was needed to rank hurricane destructiveness. Saffir had some “Richter envy” from observing the ease with which seismologists now communicated with the public. In 1971, he contacted Robert Simpson, head of the National Hurricane Center to help link damage levels with wind speeds.
Seeing the opportunity to communicate evacuation warnings, Simpson also added details around the height of advancing storm surges. Better information was clearly needed, after the loss of life in Hurricane Camille on the Mississippi coast in 1969.
Climate modeling studies generally agree that anthropogenic climate change will likely cause tropical cyclones globally to be more intense on average, and that the most powerful ones will become more frequent. In response, climatologist Michael Mann (particularly well known for his so-called “hockey-stick” temperature graph) recently advocated the introduction of a sixth category to the Saffir-Simpson Hurricane Wind Scale (SSHWS), in order to better describe the very strongest storms. According to Mann, sturdier construction practices mean that Category 5 storms no longer all cause near-total destruction of human infrastructure and introducing a Category 6 would increase public awareness of the effects climate change is having on tropical cyclone strength. Mann is not the first to propose introducing a Category 6; after powerful tropical cyclones make landfall this is frequently deliberated. Before wading into this debate however, let us look at the SSHWS itself.