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Before Hurricane Harvey, Ocean Heat Was at Record Levels in the Gulf, Feeding Storm's Record Rain, Study Finds

At a Glance

Ocean heat content was the highest on record globally before the start of summer 2017.
The heat loss in the Gulf of Mexico during Hurricane Harvey matched the latent heat released by the hurricane's rainfall along the Gulf Coast.
Therefore, the latent heat fueled the storm, a new paper concluded.
Many vulnerable areas are suffering major consequences from climate change due to the lack of essential adaptation.

Ocean heat content was the highest on record both globally and in the Gulf of Mexico before the start of summer 2017. That heat supercharged Hurricane Harvey, allowing it to dump record rain in southeastern Texas in late-August 2017, according to a new paper released Tuesday in the online journal Earth's Future.

The moisture in the air that evaporates from warm oceans is what fuels hurricanes. When that moisture condenses into raindrops, latent heat – the ocean heat that caused the moisture to evaporate – is released and fuels the storm. The higher the amount of latent heat, the larger and stronger the hurricane will grow, leading to heavier rain.

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Oceans continue to warm as the Earth's climate changes, leading to higher ocean heat content and warmer sea-surface temperatures. The effects are becoming evident in tropical cyclones: they are larger, more intense and longer-lasting, the study's lead author, Kevin Trenberth of the National Center for Atmospheric Research (NCAR), noted in the paper.

Hurricanes are primarily treated as a weather phenomenon, but Trenberth believes they are more of a climate phenomenon because of the very strong role the ocean plays in the formation and intensity of these powerful tropical cyclones.

Visible satellite imagery shows Hurricane Harvey off the coast of southeastern Texas nearing landfall on Aug. 25, 2017.
(CIRA/RAMMB)

As tropical cyclones feed on latent heat, ocean temperatures cool in the vicinity of the storm as heat is lost.

Trenberth and his research team found that the heat loss in the Gulf of Mexico during Harvey matched the latent heat released by the hurricane's rainfall along the Gulf Coast, concluding that the latent heat fueled the storm.

"Without so much ocean heat and moisture supply, the rainfall would not have been anything like as much," Trenberth said in a news release summary Tuesday. "In this way, a direct link to global warming from human-induced heat-trapping gases in the atmosphere is established."

The paper added that hurricanes play a key role in the Earth's climate system: they pump heat out of the warm tropical oceans, keeping water temperatures cooler. Once that heat enters the atmosphere, it's dispersed by the wind and can eventually be radiated into outer space.

"In this way, the hurricanes act as a relief valve for the ocean; they result in somewhat cooler conditions but at the expense of a severe storm," Trenberth said.

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The paper noted that planning for supercharged hurricanes, such as Harvey, is essential. This should include updating building codes, electrical systems and flood-control systems, preparing more evacuation routes and planning for long-term power outages.

However, the authors concluded that these improvements may not be adequate in many areas, including Texas, Florida and Puerto Rico – some of the hardest-hit areas during Harvey, Irma and Maria last year.

"Proactive planning for the consequences of human-caused climate change is not happening in many vulnerable areas, making the disasters much worse," said Trenberth.

Brian Donegan is a meteorologist at weather.com. Follow him on Facebook, Twitter and Instagram.