Why you shouldn’t only use a hurricane’s “Category” in determining your emergency plan

Why you shouldn’t only use a hurricane’s “Category” in determining your emergency plan
Breaking down the Saffir-Simpson Scale

MYRTLE BEACH, SC (WMBF) - A common phrase we hear during a hurricane season is “I will only evacuate if the hurricane is a category 3,” for example. Here’s more on a hurricane’s category and why you should look beyond using just the number when putting together your plan.

1. Hurricane’s Category is based on only ONE factor

The Saffir-Simpson scale, which assigns a Category of 1 to 5 for hurricanes, only uses maximum sustained wind speeds as a determining factor. The scale is designed to be straight-forward, but doesn’t include many of the most damaging impacts of a hurricane.

Flooding potential and storm surge impacts are NOT included and can cause more damage than winds. In newly released government data, the Congressional Budget Office estimates $34 Billion of total residential storm damage from the 2018 Atlantic Hurricane season. $20 Billion of damage is associated with flooding while, the CBO estimates $14 Billion of damage came from winds.

The scale also doesn’t include all wind speeds. According to the National Hurricane Center, the scale uses “Sustained winds” estimating the wind speeds for 1 minute intervals. This does NOT include stronger wind GUSTS, which can last less than a minute. These gusts, even if they only last a few seconds, can produce widespread damage and power outages. In short, the sustained winds don’t reflect the full strength of the winds within a hurricane.

The category also doesn’t include the tornado threat, which mainly depends, not on the wind speed, but on where the hurricane makes landfall along the coast.

2. Category number can change

As we saw when tracking Hurricane Florence the Category will fluctuate as more data comes in, even within hours of making landfall. In the days ahead of Hurricane Florence, its projected Category 4 intensity resulted in many evacuating earlier. By the time it got closer to shore and made landfall that Friday morning, it only maintained a Category 2 wind strength. Basing your evacuation plan solely around single number that can change isn’t going to help you understand the wide swath of impacts associated with a hurricane.

3. Every hurricane has its own character, even if they are the same Category

A hurricane’s impacts are different for each storm and also depend on the hurricane’s structure and movement. The Saffir-Simpson scale doesn’t take into account the hurricane’s size, its speed, duration or the angle of the landfall. As we saw with Hurricane Florence, it crawled to 1 MPH of forward speed once it made landfall, allowing for extremely heavy rain to fall over the same areas for longer periods of time. According to the National Hurricane Center, hurricanes can also range in size from a diameter of over 800 miles with Category 2 Hurricane Sandy in 2012 to as small as 77 miles with Category 1 Hurricane Franklin in 2017.

Bottom line:

Prepare for each individual hurricane as if it is a new one.

Don’t let a previous Category number dictate what your plan for a new hurricane should be.

Use reliable sources of information to make your decision. Follow along with the frequent updates on the WMBF First Alert Weather App. It is free and has valuable video tools from our meteorologists, and the local impacts expected from hurricanes and tropical systems. Our radar also features the “Tropical Tracker” feature to keep an eye on what is brewing out at sea.

Copyright 2019 WMBF. All rights reserved.