Four of the 10 costliest hurricanes on record in the United States occurred in 20. While there have been extreme storms in the past, recent history reflects the growing expense of hurricanes. This increase in frequency is correlated with the rise in North Atlantic sea surface temperatures, which could be partially related to global warming.Ĭlimate change is adding to the coast and threat of hurricanes. In the North Atlantic Basin, the long-term (1966-2009) average number of tropical storms is about 11 annually, with about six becoming hurricanes. More recently (2000-2014), the average is over 15 tropical storms per year, including about seven hurricanes. Others include its track (the site where the storm makes landfall), size, storm structure, rainfall amount, duration, and the vulnerability of the area it affects.įrequency and intensity vary from basin to basin. Wind speed is just one of many factors that contribute to a hurricane’s impact. Storms with winds stronger than 111 mph are considered “major hurricanes” (Category 3 or higher). A storm with winds exceeding 74 mph is a Category 1 hurricane. The National Hurricane Center categorizes Atlantic hurricanes based on wind speed. Weaker tropical cyclones might be called “ tropical depressions” or “ tropical storms.” Stronger systems are called “ hurricanes” or “ typhoons,” depending on where they form. In the Southern Hemisphere, they rotate clockwise. In the Northern Hemisphere, these storms rotate counter-clockwise. More recent work shows a trade-off between intensity and frequency – that as warmer oceans bolster hurricane intensity, fewer storms actually form.īackground on Hurricanes and Tropical StormsĪ hurricane is a type of tropical cyclone, which is a general term for a low-pressure system with activity like thunder and lightning that develops in the tropics or subtropics. For the 21 st century, some models project no change or a small reduction in the frequency of hurricanes, while others show an increase in frequency. It is likely the number of storms will remain the same or even decrease, with the primary increase being of the most extreme storms. The connection between climate change and hurricane frequency is less straightforward. The changing patterns of tropical storms (a shift northward in the Atlantic) could put much more property and human lives at risk, but much more research is required to build a better understanding of how these patterns might change. This is likely associated with expanding tropics due to higher global average temperatures. Much of this damage was related to coastal flooding.Īreas affected by hurricanes are shifting poleward. For example, sea level rise intensified the impact of Hurricane Sandy which caused an estimated $65 billion in damages in New York, New Jersey, and Connecticut in 2012. Globally averaged, sea level is expected to rise by 1-4 feet in low and moderate emissions scenarios during this century, which will amplify coastal storm surge. Sea level rise is likely to make future coastal storms, including hurricanes, more damaging. Recent storms such as Hurricane Harvey in 2017 (dropping over 60 inches in some locations), Florence in 2018 (with over 35 inches) and Imelda in 2019 (44 inches) demonstrate the devastating floods that can be triggered by these high-rain hurricanes. Warmer sea temperatures also are causing hurricanes to wetter, with 10-15 percent more precipitation from cyclones projected in a 2 degree C scenario.
Based on complex modeling, NOAA has suggested that an increase in Category 4 and 5 hurricanes is likely, with hurricane wind speeds increasing by up to 10 percent. Warmer sea surface temperatures could intensify tropical storm wind speeds, potentially delivering more damage if they make landfall. Hurricanes are subject to a number of climate change-related influences: Stronger hurricanes will be far more costly in terms of damages and deaths without action to make coastal (and inland) areas more resilient. Although scientists are uncertain whether climate change will lead to an increase in the number of hurricanes, there is more confidence that warmer ocean temperatures and higher sea levels are expected to intensify their intensity and impacts.