Inside Tropical Cyclones--Part 3: Impacts from Landfalling Hurricanes and Tropical Storms

Tropical storms and hurricanes are truly some of the most fascinating type of weather systems to study. They begin as a complex of thunderstorms, but morph into spiraling, destructive, and deadly forces of nature. Whenever a tropical storm or a hurricane makes landfall, the impact can be devastating if the right or wrong conditions come together.

WIND AND STORM SURGE

Tropical storms and tropical depressions usually do not have a major impact in terms of wind damage, unless the areas they affect have exceptionally weak infrastructure. Impacts from wind become more severe, however, with a hurricane. Hurricanes are categorized on a 1-5 scale, the Saffir-Simpson Scale. This scale also describes the type of damage that may result from the wind in a hurricane. While the most intense winds usually occur near the eye wall and closest to where the system makes landfall, major wind damage can extend farther inland, especially in a major hurricane.

The Saffir-Simpson Scale for Hurricanes

The strongest winds occur on the side of the eye wall that combines the storm's forward motion with the maximum sustained wind. For instance, in a westward moving hurricane, the strongest winds will occur on the northern eye wall.

Inland forest of pine trees snapped from Hurricane Michael. Photo: USDA

Storm surge is another major hazard for those who live on coastal areas in hurricane prone regions. Storm surge is the inundation and rapid rise of water transported from a large body of water, such as the Gulf of Mexico, Atlantic Ocean, or even a bay, to nearby locations resulting in significant flooding. Storm surge is one of the main reasons many flood prone areas are placed in evacuation orders. In general, a stronger hurricane will produce greater storm surge. The strength of the hurricane, however, is not the only factor that should be considered when preparing or responding to storm surge. Coastal shape, slope, soil type, and topography also play a major role in this factor. The most dangerous scenario for a storm surge event would be a combination of incredibly high storm surge occurring simultaneously with high tide.

St. George Island, Florida before and after Hurricane Michael. Photo: USGS

INLAND FLOODING

One aspect of a landfalling tropical system that does not get as much attention as damaging winds or storm surge is the potential for major inland flooding. In fact, a weak tropical storm or a tropical depression can cause a catastrophic inland flooding event. Classic examples of this occurring are Texas's Tropical Storm Allison (2001) and Tropical Storm/Depression Harvey (2017). According to the USGS, rainfall from Hurricane Harvey alone "exceeded 60 inches in some locations, which is 15 inches more than the average annual amounts of rainfall for eastern Texas and the Texas Coast."

When the steering currents in the upper atmosphere are extremely weak after a tropical system makes landfall, this can lead to a prolonged threat for very heavy rain, especially if the tropical cyclone is able to tap into a rich moisture source. Unfortunately, the Saffir-Simpson scale does not completely account for the impact from an inland flood event. This is why it is extremely important for those in the path of a hurricane or tropical storm to not only focus on the category number, but also the impact from hazards such as inland flooding.

Stay safe, stay informed, and stay prepared this Hurricane Season. Heed the advice of local officials, and remember that it is better to evacuate if told to evacuate than to stay behind and put yourself and emergency workers in a life-threatening situation.