Climate Change is Making Atlantic Hurricanes Wetter and Faster to Gain Strength but Not Stronger, Bigger, or More Frequent: Models Predict Wetter Hurricanes

     It’s no secret that the waters in the Atlantic Ocean and the Gulf of Mexico are hotter than they have ever been in recent history. Climate modeling predicts that storms moving through those areas will pick up more moisture allowing for bigger and wetter storms. Sea level rise, partially from global warming but also due to other factors, means that storm surges will be maximized.

     When I see some of my energy industry colleagues posting about how climate change is overblown, often using data that is irrelevant, I think they are just rationalizing their own political views against any kind of climate action. While what policy and adaptation actions we should pursue is quite debatable, it is not rational to do nothing. We know that population and development have grown faster than the national average in areas vulnerable to hurricanes and prone to wildfires. That is simply not smart. It may be warm in Florida, but it is a dangerous place in terms of storms. Helene’s jaunt through the Southern Appalachian Mountain region was unprecedented and unexpected. The size of the storm was massive and the amount of rain it carried and released was massive. The models predict hurricanes with higher rainfall amounts.

     I remember 15 or 20 so years ago when climate models were predicting more hurricanes but that failed to happen. It seems that warm waters may not influence the early development of storms as much as they influence storms already developed and on the move. We saw it with Hurricane Harvey dumping record amounts of rainfall along the Texas Gulf Coast and far inland in 2017. Several other hurricanes were noted to be carrying higher moisture levels and with Helene, we are reminded again of the power of hurricanes to cause inland flooding, hundreds of miles from the coast. We have had hurricane flooding in Ohio many times. However, the moisture carried by hurricanes has gone up in recent years.

     Looking at data from the NOAA’s National Hurricane Center, I plotted Category 4 and 5 hurricane hits. The data show that storms of this intensity remained consistent in number. From 1950-1987 the number of Cat 4 and 5 hurricanes was roughly the same as between 1987-2024. Thus, I would conclude that hurricanes are not becoming more intense.

Data Source: NOAA National Hurricane Center

     Hurricanes are not getting more numerous as early climate models erroneously predicted. According to Wikipedia:

“The 1990s were the most active decade for the United States, with a total of 31 hurricanes affecting the nation. By contrast, the least active decade was the 1860s and 1970s, each with a total of only 15 hurricanes affecting the United States. A total of 33 seasons on record passed without an Atlantic hurricane affecting the country — the most recent of which was the 2015 season. Seven Atlantic hurricanes affected the country in the 1886 season, which was the year with the most United States hurricanes.”

     As I understand it (October 8, 2024) Hurricane Milton is the fastest storm ever to go from tropical storm to Category 5. That is thought to also be due to the warmer Gulf waters.

     The intensity and wind speed of a hurricane at landfall do not always equate to the impacts. Path relative to population, population vulnerability, preparation, amount of rain, rate of rain, and storm surge are other factors. Category 1 to 3 hurricanes have also had bad impacts.

     A 2022 study in Nature Communications concluded that 2020 tropical storms and hurricanes carried up to 10% more water due to climate change:

 

“…human-induced climate change increased the extreme 3-hourly storm rainfall rates and extreme 3-day accumulated rainfall amounts during the full 2020 hurricane season for observed storms that are at least tropical storm strength (>18 m/s) by 10 and 5%, respectively. When focusing on hurricane strength storms (>33 m/s), extreme 3-hourly rainfall rates and extreme 3-day accumulated rainfall amounts increase by 11 and 8%, respectively.”

    

     Rainfall amount comparisons are difficult to compare as the graph below from the paper shows, comparing rainfall amounts and hurricane tracks. Hurricanes carrying higher amounts of moisture also carry higher amounts of risk since flooding is second only to storm surges in hurricane fatalities.

 

     Some evidence suggests that hurricanes are maintaining strength longer after landfall and that they may move slower over land. That seemed to be the case with Hurricane Harvey in 2017. It moved very slowly, causing severe flooding in Southeast Texas.

     I looked for evidence that hurricanes may be becoming bigger but that does not seem to be the case. The biggest storm ever recorded in the Atlantic was Typhoon Tip in 1979. It was in the North Atlantic and did not make landfall. Its diameter was about 1250 miles (2000km). This Category 5 hurricane was also the most intense hurricane ever recorded.

     There is evidence that hurricanes have gotten slightly more intense in terms of wind speed but the overall change has not been that much and is not a definite trend that can be definitively associated with climate change.  

     Other research shows that large and extreme floods have been increasing in frequency from 1985 to 2020 as the graph below confirms. According to a Phys.org article about the DFO Flood Observatory (formerly the Dartmouth Flood Observatory):

 “It's not the case that the world is getting wetter. In fact, many places are becoming more arid. Rather, really big floods, which were previously rare, are happening more often.”

“According to Kettner, the reasons behind this are hard to parse out. In some cases, it could be that warmer air temperatures allow the atmosphere to hold more moisture. In other cases, extreme flooding might be driven by urban infrastructure that lacks adequate drainage. Most of the underlying causes of catastrophic floods boil down to two categories: climate change and human changes to the landscape.”

"Flooding is both a derivative of precipitation and the area where that precipitation is landing," Kettner explained.

 

References:

 

Tropical Cyclone Climatology: NOAA. National Hurricane Center. Tropical Cyclone Climatology (noaa.gov)

List of United States hurricanes. Wikipedia. List of United States hurricanes - Wikipedia

Historical Changes in Atlantic Hurricane and Tropical Storms. Gabriel A. Vecchi and Thomas R. Knutson. Geophysical Fluid Dynamics Laboratory. 2008-2011. Historical Atlantic Hurricane and Tropical Storm Records – Geophysical Fluid Dynamics Laboratory (noaa.gov)

Are hurricanes getting worse? Here’s what you need to know. Rachel Waldholz and Alyson Hurt. NPR. Climate. October 8, 2024. How climate change makes hurricanes worse : NPR

Hurricanes may not be becoming more frequent, but they’re still more dangerous, Carolyn Gramling. Science News. July 13, 2021. Hurricanes are getting more dangerous, but may not be more frequent | Science News

A Force of Nature: Hurricanes in a Changing Climate. NASA Science Editorial Team. June 1, 2022. A Force of Nature: Hurricanes in a Changing Climate - NASA Science

Attribution of 2020 hurricane season extreme rainfall to human-induced climate change. Kevin A. Reed, Michael F. Wehner & Colin M. Zarzycki. Nature Communications volume 13, Article number: 1905 (April 2022). Attribution of 2020 hurricane season extreme rainfall to human-induced climate change | Nature Communications

Hurricanes are maintaining their strength farther inland as the planet warms, study finds. Drew Kann, CNN. November 11, 2020. Hurricanes are maintaining their strength farther inland as the planet warms, study finds | CNN

Extreme floods, like those caused by Hurricane Helene, are becoming more frequent. Gabe Allen. Phys.org. October 10, 2024. Extreme floods, like those caused by Hurricane Helene, are becoming more frequent (msn.com)