Climate Matters•September 23, 2020
Stronger Hurricanes
KEY CONCEPTS
Sea surface temperatures in the tropical Atlantic, known as the Main Development Region for tropical systems (depressions, storms, and hurricanes), have risen 1.85°F in the last century.
The likelihood of tropical cyclones (the term scientists broadly use to represent hurricanes, typhoons, etc) reaching Category 3 status has increased since 1979.
Warming water and air from climate change creates the potential for stronger hurricanes, with heavier rain and higher storm surge, increasing the risk of flooding when they make landfall.
The 2020 Atlantic hurricane season is already the second most active on record, and the entire list of storm names has been exhausted. As a result, the remaining storms this season will take their names from the Greek alphabet. The only other time this happened was 2005, when there were four storms that reached Category 5 - Emily, Katrina, Rita, and Wilma. While there are year-to-year variations in weather patterns and water temperatures that lead to one season being more active than another, climate change is making the storms worse once they develop.
Even though the overall number of hurricanes each year is not increasing, there is a significant increase in the likelihood that a hurricane will be at major hurricane (Category 3-5) intensity during its lifetime. A NOAA CIMSS study earlier this year re-examined global satellite data from 1979 to 2017. Using the regular intensity estimates that are available every 6 hours (known as fixes), scientists found that the probability of a hurricane reaching a Category 3 or higher has increased at about 8 percent per decade globally. When examining only the North Atlantic, that number jumped to 49 percent per decade. Combining those fixes into 3-year periods, the proportion of fixes indicating a major hurricane jumped from about 32 percent to 39 percent globally, and from about 15 to 38 percent in the North Atlantic.
Water temperatures in the tropical Atlantic during hurricane season have risen about 1.85°F over the past hundred years. When combined with the warming atmosphere, this means storms have a greater potential for strengthening — sometimes rapidly — leading to greater impacts on people. More water evaporates into the storms, allowing for heavier rain. There is also evidence that the forward speed of storms is slowing, increasing rainfall amounts over a particular place and adding to inland flooding risk. And with sea levels averaging 7 inches higher than a century ago, coastal flooding from storm surge is already deeper and traveling farther inland.
Without cuts in greenhouse gas emissions, these trends will continue, with higher coastal inundation levels, higher rainfall rates, and a higher percentage of storms reaching major hurricane status.
POTENTIAL LOCAL STORY ANGLES
Are you in a coastal state and want to know what a storm surge prediction means for your area?
When a storm surge is projected for your area, Climate Central’s Risk Finder tool allows you explore the populations, properties, and infrastructure at risk at various water levels. Following a storm’s damage, many communities and individuals are faced with questions about rebuilding and relocating. Our Coastal Risk Screening Tool allows users to view U.S. and global coastal locations threatened by sea level rise and coastal flooding both now and decades into the future.
You don’t have to be on the coast to experience heavy precipitation from a hurricane. Want to know what typically floods near you?
FEMA collects information on flood insurance for each state and you can check out NOAA’s interactive billion-dollar weather and climate disasters website to find historic events near you. Using FEMA data, the National Resources Defense Council has created an online tool to find repeatedly flooded properties in each state and county, along with National Flood Insurance Program claims. Pew Charitable Trusts has compiled research on local flood mitigation efforts around the country, and the National Conference of State Legislatures collects resources on state level actions on flood issues.
RESOURCES
NOAA National Hurricane Center (aka NHC)
Storm Surge: Planning for the Risk « Inside the Eye (NOAA NHC)
National Flood Insurance Program Community Rating System (FEMA)
Global Warming and Hurricanes - FAQ’s from NOAA Geophysical Fluid Dynamics Lab
Hurricanes and Typhoons - Fourth National Climate Assessment (Part 1 - Climate Science Special Report)
Quick Facts - Hurricanes and Climate Change (SciLine)
LOCAL EXPERTS
The National Center for Atmospheric Research has several scientists available to speak about hurricanes, including some working with the insurance industry to better understand impacts. The SciLine service, 500 Women Scientists or the press offices of local universities may be able to connect you with local scientists who have expertise in your area. The American Association of State Climatologists is a professional scientific organization composed of all 50 state climatologists. The Association of State Floodplain Managers (ASFPM) has 37 state and regional chapters that can discuss local flood events and policies to mitigate current and future losses from flooding.
NATIONAL EXPERTS
Jim Kossin, Ph.D. Climate Scientist, NOAA National Centers for Environmental Information (NCEI). Research focuses on tropical meteorology and impacts of climate change. Lead author of the above study. kossin@ssec.wisc.edu
Kerry Emanuel, Ph.D. Professor of Atmospheric Science, MIT. Research focuses on tropical meteorology and climate change. emanuel@mit.edu
Athena Masson, Ph.D. Meteorologist and hurricane specialist for Florida Storms and the Florida Public Radio Emergency Network (FPREN) at the University of Florida. amasson@ufl.edu
Jhordanne Jones, Doctoral Candidate, Department of Atmospheric Science, Colorado State University Tropical Meteorology Project. jhordanne.jones@colostate.edu
Jamie Rhome, Storm Surge Specialist/Team Lead, National Hurricane Center. jamie.r.rhome@noaa.gov
*Gabriel Vecchi, Ph.D. Professor of Geosciences, Princeton Environmental Institute. Research focuses on tropical meteorology and climate change. gvecchi@princeton.edu
*Available for interviews in Spanish
METHODOLOGY
Trends in hurricane intensity based on Kossin et al. (2020), see paper for full methodology. Proportions are for major tropical cyclones (Category 3-5) compared to all tropical cyclones that are Category 1 or higher. Water temperature data from 1910 to 2019 in the tropical Atlantic is based on the Atlantic Main Development Region from NOAA Climate at a Glance. While there are small amounts of land within the area, ocean anomalies dominate the value. It is effectively, but not purely, a measure of the sea surface temperatures there. Anomalies are relative to the 1910-2000 average. Hurricanes are the regional name given to tropical cyclones, which are known as typhoons in the western Pacific Ocean.