Hurricane Florence is undoubtedly a life-threatening, perhaps unprecedented colossus. As spotted by Earther’s Brian Kahn, a visualization of the predicted storm surge by The Weather Channel really hammers home just how lethal Florence could be.
Aside from its inherent terror, this video also nicely demonstrates that wind speed is a pretty poor way of measuring the damage potential of a hurricane.
The Saffir-Simpson Hurricane Wind Scale (SSHWS), developed in 1971 by a civil engineer and a meteorologist at the National Hurricane Center (NHC), relies on putting hurricanes in various categories – 1 to 5 – based on wind speed. This wasn’t always the case: storm surges and the central peak pressure were used until 2010, when the scale was simplified.
Wind speed is a proxy for the energy of a hurricane, sure, but most of the energy used by hurricanes isn’t in wind formation.
The “average” hurricane unleashes around 603 trillion joules every single second, but the amount that’s released through cloud and rain formation is 400 times that involved in kinetic energy-driven wind production. Sure, strong winds can cause damage and steal lives, but it’s the inundation that’s the major problem here.
The reason Hurricane Harvey was so dangerous wasn’t really related to its category, but the fact that it dumped a lot of rainfall in one place. Its water capacity, plus the fact that it stalled over Houston, were key.
That’s why reports that Hurricane Florence has weakened are perhaps misleading. It may be losing energetic steam, but it’s still a monster that'll cause plenty of flooding.
Flooding doesn’t just come from rainfall, of course. That’s where the beautifully rendered storm surge comes in, which is normally the deadliest part of a hurricane.
Hurricanes are low-pressure beasts, so when they move over shallow water, it rises a little in response. At the same time, the force of the winds pushes plenty of water towards the shore, where it piles up.