Atlantic Hurricanes: classification and inland impacts

Hurricane Erin made headlines along the east coast of the U.S. this week, bringing high surf, rip currents, and coastal flooding from the Carolinas to the Northeast despite never officially making landfall.

Erin is bound to be the first of many more hurricanes to develop within the Atlantic basin this year, where hurricane season runs from June 1 to November 30, peaking between mid-August and mid-October. 

In the Northern Hemisphere, tropical cyclones rotate counterclockwise and are classified by wind speed. A tropical cyclone is categorized in four different ways: tropical depression, tropical storm, hurricane, and major hurricane. Each of these classifications is defined by maximum sustained wind speeds. 

A tropical depression has maximum sustained winds of 38 mph or less, while a tropical storm has winds ranging from 39 to 73 mph. When a tropical cyclone reaches sustained winds of 74 mph or higher,  it is categorized as a hurricane using the Saffir-Simpson Hurricane Wind Scale. 

This scale places hurricanes into five different categories. Categories 1 and 2 include storms with winds between 74 and 110 mph, while categories 3, 4, and 5 are considered major hurricanes with sustained winds of 111 mph or higher. Maximum sustained winds within a category 4 hurricane range from 130 mph to 156 mph, and the highest winds in a category 5 storm reach over 157 mph. 

Notably, the most intense wind field within the eye wall of a major hurricane is usually within a 30 to 70-mile radius from the eye. Hurricane-force winds of 74 mph or higher can extend well over 100 miles from the center of circulation. 

As major hurricanes make landfall, they tend to weaken rapidly on their journey inland. Here in the Midwest, the remnants of landfalling tropical systems rarely bring impactful winds, but can produce heavy rainfall on a fairly large scale.

In some cases, tropical rains are beneficial, but they can also contribute to impactful flood events. The remnants of tropical systems can also produce small tornado outbreaks as far north of the Midwest, generating enough wind shear to support small, low-end tornadoes given the right environment.