Why Hurricanes Linger More Now After Landfall

Hurricanes are lasting longer and staying stronger after landfall, according to new research.

That means inland areas could face increasing danger from hurricanes, and residents and emergency managers in those areas might have to be on guard for future storms in much the same way as those along the coast.

The study, published Wednesday in the journal Nature, attributes the phenomenon to climate change, specifically warmer ocean temperatures caused by global warming.

Normally, a hurricane's strength drops over land, once it is no longer fueled by the ocean. But the researchers found that hurricanes carry more moisture when they develop over warmer oceans, which means a hurricane has extra fuel to potentially sustain itself longer and at a higher intensity after landfall.

“Hurricanes are heat engines, just like engines in cars. In car engines, fuel is combusted, and that heat energy is converted into mechanical work," Lin Li, co-author of the study and a doctoral student at the Okinawa Institute of Science and Technology Graduate University in Japan, said in a news release. "For hurricanes, the moisture taken up from the surface of the ocean is the 'fuel' that intensifies and sustains a hurricane’s destructive power, with heat energy from the moisture converted into powerful winds,"

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Li and study co-author Pinaki Chakraborty, a professor at the Okinawa institute, analyzed storms that made landfall over North America between 1967 and 2018. The data showed that a hurricane in the late 1960s lost about 75% of its intensity in the first day after landfall. By 2018, that had dropped to 50%.

The change happened at the same time that land and sea surface temperatures are rising. Earth's 10 warmest years on record have all occurred since 1998, according to NOAA. Nine of the 10 happened since 2005.

The researchers also modeled virtual storms at various ocean temperatures and simulated landfalls as Category 4 hurricanes. The models showed a correlation between longer duration and intensity and warmer ocean temperatures. Further simulations showed that moisture gave the hurricanes an extra boost.

“This shows that stored moisture is the key factor that gives each hurricane in the simulation its own unique identity,” Li said. “Hurricanes that develop over warmer oceans can take up and store more moisture, which sustains them for longer and prevents them from weakening as quickly.”

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More moisture in hurricanes can also lead to more rainfall, which is the biggest inland threat, according to research from the National Hurricane Center. Hurricane Harvey in 2017 and Hurricane Florence in 2018 are two of the most recent examples of hurricanes that hovered over land and caused disastrous flooding.

While there haven't been any long-lasting hurricanes over land in the U.S. so far this year, there have been significant inland impacts. Of the six people killed by Hurricane Zeta in October, for example, four died when trees fell on them, hundreds of miles from where the storm made landfall. Zeta and Hurricane Isaias, which hit in August, each caused millions of power outages across multiple states.

Previous research has already shown that hurricanes are becoming more intense because of global warming. A study earlier this year by NOAA and the University of Wisconsin-Madison Cooperative Institute for Meteorological Satellite Studies (CIMSS) showed a significant increase in tropical cyclone activity worldwide from 1979 to 2017.

“We know that coastal areas need to ready themselves for more intense hurricanes, but inland communities, who may not have the know-how or infrastructure to cope with such intense winds or heavy rainfall, also need to be prepared," Chakraborty said. "If we don’t curb global warming, landfalling hurricanes will continue to weaken more slowly. Their destruction will no longer be confined to coastal areas, causing higher levels of economic damage and costing more lives.”

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