Tropical Cyclones

When tropical cyclones encounter land, their intense rains and high winds can cause severe property damage, loss of life, soil erosion, and flooding. The associated storm surge—the large volume of ocean water pushed toward shore by the cyclone’s strong winds—can cause severe flooding, additional erosion, and extensive destruction.

Warmer oceans produce more evaporation, which means more water is available in the atmosphere as water vapor and allows for more rain. This increased rain releases more heat and amplifies winds around the core of the cyclone. These climate amplified tropical cyclones have caused over $1,333 billion in damages since 1980.

What is a Tropical Cyclone?

A tropical cyclone is a generic term for a low-pressure system which forms in the tropics or subtropics and is accompanied by thunderstorms organized into rain bands. In the Northern Hemisphere, tropical cyclones have a counterclockwise circulation of winds near the earth’s surface. Tropical cyclones do not have cold or warm fronts attached; those systems are called extratropical cyclones.

Tropical cyclones are categorized based on maximum sustained wind speeds:

• Tropical Depression: A tropical cyclone with maximum sustained winds of 38 mph or less.
• Tropical Storm: A tropical cyclone with maximum sustained winds of 39 to 73 mph.
• Hurricane: A tropical cyclone with maximum sustained winds of 74 mph or higher.
• Major Hurricane: A tropical cyclone with maximum sustained winds of 111 mph or higher, corresponding to a Category 3, 4, or 5 on the Saffir-Simpson Hurricane Wind Scale.

Are tropical cyclones becoming more severe?

Over the 39-year period from 1979-2017, the number of major hurricanes has increased while the number of smaller hurricanes has decreased. Over twelve days in September 2022, 7 record-setting cyclones swirled across the globe, impacting millions of people.

NOAA identified a pronounced increase in Category 4-5 intensity storms since the mid-1940s and predicts a continuing increase in major hurricanes. Due to the worsening climate, the next 75 years will see an expansion of tropical cyclones into mid-latitude regions to include major cities like New York and Boston.

Damages to Critical Infrastructure from Tropical Cyclones

Tropical cyclones produce torrential flooding, damaging winds, tornadic activity, erosion, hail, storm surge, and coastal flooding within their storm path which can span numerous states and cause severe damage to critical infrastructure systems. Most damage is caused by copious amounts of water and/or high winds brought about by the tropical storms.

Impact of Heavy Rains and Flooding

Flooding damages to energy infrastructure are considerably higher from tropical weather as a combination of overflowing rivers, storm surge, and torrential rains can compound to result in standing water able to reach 1-story deep. Flooding can cause prolonged power outages which can stop elevators, hinder remote entry points, impede refrigeration, disrupt emergency services sites, and damage security features state facilities need to operate.

Sudden heavy floodwaters can severely degrade earthen and lined irrigation canals through increased rates of subsidence, erosion, or sediment flows. Flash flooding may carry high levels of raw sewage and debris into waterways and local wells, overwhelming intakes for water treatment facilities and impacting local and regional drinking supplies.

Storm surge and coastal inundation of roadways, pipelines, runways, and railways can result in erosion of material, reduced load bearing capacity of material, sinkholes, and debris flows. Sinkholes can form from water weight damaging the structural integrity of sewer systems or from compromised soil composition such as eroded surface rock.

Impact of Powerful Winds

Tropical cyclone winds can damage site integrity and equipment in a wider swath than most tornado events. Continuous winds from thunderstorms in the rainbands and associated with the eyewall can cause tornadic strength gusts to persist for hours to days. Most powerlines can withstand winds around 55mph, while severe storms in rainbands can produce sustained winds over 75 mph and gusts near 160 mph.  

Power outages and physical damage caused by severe weather can impact all aspects of communication, transportation, emergency services, and water systems. As the cyclones move inland, impacts from the storm often continue to pose a significant threat to infrastructure across multiple regions.