Why a Hurricane's Size and Speed Matter as Much as Its Category

All eyes are on the Gulf Coast and the Southeast as Isaias makes its way to the region. While most forecasts focus on the category of a tropical weather maker, experts note that that is not the only metric that matters. A storm's Saffir-Simpson Hurricane Wind Scale category designation simply takes into account its wind speed, falling on a scale of 1 to 5. This is undoubtedly an important metric, but it is not the only factor that influences the overall impact of a storm.

Here are the two other important factors to consider when evaluating your personal risk.

Speed of the Storm

The large-scale winds surrounding a storm determine how fast it is moving. Fast steering winds naturally support a faster storm speed. Conversely, a storm is more likely to slow its speed if the steering winds are weak. According to NOAA's Hurricane Research Division, the average speed of a hurricane churning in the lower altitudes is 10 to 13 mph.

Why does speed matter? Storms moving at a fast clip are more difficult for forecasters to monitor. It stands to reason that this unpredictability makes it more challenging for residents in the path to prepare for impact. Faster-moving storms also come with stronger winds to the right of the eye, resulting in a greater degree of impacts for those in this path. Lastly, storms chugging along are able to send their strong winds farther inland before they weaken.

On the other hand, slow creepers give people more time to prepare for the impending arrival. However, these crawlers also come with the threat of prolonged impacts, as it takes longer for the storm to exit the region. This means that those in the line of fire could be dealing with hurricane-force winds and destructive storm surge for hours.

Most consequentially, the speed of the storm also determines how much rain falls over any given area. Areas that get caught up in a storm that is slowing its speed should be prepared for more significant impacts.