Landfall vs. Direct Impact: Why the Difference Matters So Much

The surge of tropical weather activity in the Pacific provides a good illustration of the difference between a landfall and direct impacts. This is what you need to know about these two terms.

Tropical Weather Does Not Have to Make Landfall to Produce Severe Impacts

Many people focus on whether a tropical storm or hurricane is making a direct impact when assessing the potential hazards. However, a storm can remain well offshore and still cause what is known as "direct impacts."

A hurricane makes landfall when the center of the system comes ashore. This landfall is tied to a specific location. But the storm's dangerous winds, rain, storm surge, and rough seas extend far out from the center or point of landfall. A forecast track only follows the path of the center of the storm, rather than the full scope of the dangers.

The recent Hurricane Lowell is a good example of a storm that did not make landfall but still caused significant damage to the Hawaiian island of Kauai. Lowell unleashed 21.1 inches of rain at Kilohana and winds that eclipsed the 90-mph barrier, despite the center of the storm never crossing the coast.

About the Accuweather Direct-Impact Scale

Meteorological agency Accuweather has developed a direct-impact scale to better show which areas should expect meaningful tropical impacts even if a storm does not make direct landfall. According to this definition, a tropical weather event directly impacts the contiguous U.S. if it either makes landfall or delivers at least one measurable element.

These elements include rain of at least 4 inches observed at least 25 miles apart, at least five reported instances of flash flooding, at least 2 feet of storm surge encompassing 50 miles or more of coastline, or wind gusts of at least 40 mph for four hours or longer at three or more land-based observation stations at least 50 miles apart.

The definition is slightly different for U.S. islands or remote areas that do not have as many weather stations. In these areas, a direct tropical impact is defined as a landfall, wind gusts hitting at least 40 mph on one or more stations on land for three hours or longer, at least 4 inches of rain, one report of flash flooding, and storm surge of 2 feet or more.

Accuweather said that the goal of its direct-impact scale is to help those in the path understand the full scope of the storm as it approaches. By bringing the focus outside of just a direct landfall, residents are better able to prepare for what may lie ahead.

Lowell serves as a warning that a storm does not have to come ashore to create chaos. It is important to pay attention to more than just a storm's expected path. The best strategy is to monitor the local forecast for wind speed predictions, rain totals, and storm surge, keeping in mind that an event that remains offshore can still deliver life-threatening impacts.

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