Computer Simulations Show Ocean Currents Cut Hurricane Swells Down to Size

Thanks to advanced computer simulations, University of Rhode Island Graduate School of Oceanography (GSO) peer-reviewed research published in January in the Journal of Physical Oceanography, titled “Impact of Ocean Currents on Surface Waves Generated by Tropical Cyclone” claim a novel understanding of how and why strong ocean currents modify surface waves.

“Our primary finding,” says URI Professor of Oceanography Isaac Ginis, “is that hurricane-generated ocean currents can substantially reduce both the height and the dominant period of hurricane waves. The magnitude of wave reduction depends strongly on how accurately ocean currents are predicted.”

In other words, the only way to get a clear and accurate forecast of wave heights is to couple wave-ocean models. Without it, oceanographers (and surf forecasters) can’t possibly account for the buffering that takes place in ocean currents, where conveyor belts of water can run at several knots, severely altering a swell almost like a reef, a mangrove, or a low-lying barrier island.

According to Ginis, who conducted the research alongside URI GSO student (now Ph.D.) Dr. Angelos Papandreou and professor Tetsu Hara, waves are most strongly reduced by currents that the storm meets on their front-right quadrant—often dubbed “the dirty side” by meteorologists—where wind, waves, and currents tend to be strongest.

“On the front-right side of a hurricane, storm-driven currents move in the same direction as the waves. This causes the waves to travel more quickly through the high-wind region. Because the waves spend less time being energized by the wind, they do not grow as large as they otherwise would.”

This, of course, has implications for how forecasts might be read along different coasts, which, depending on storm direction and how “the dirty side” interacts with currents ahead of making land, might experience vastly different wave height reductions.

“This work has strong potential for operational use because we use the same wave and ocean models—WAVEWATCH III and MOM6—that are already part of the National Weather Service’s HAFS hurricane forecast system,” Ginis argued in a URI post spotlighting the report. “Our findings could be incorporated without major changes to existing forecasting tools. Our group has a long history of working with NOAA scientists, and results from our previous studies have already been implemented in operational hurricane models.”

Ginis et al.’s hopes are that the team’s research, which was funded by the National Oceanographic Partnership Program/Office of Naval Research, will be put to use by weather services to better predict waves during hurricanes for myriad reasons—including, for good or ill, a better surf report for one and all.