Hurricane Ivan, which caused a swathe of destruction across the Caribbean last September before crashing into the U.S. Gulf coast, generated ocean waves more than 90 feet high, researchers said on Thursday.
They may have been the tallest waves ever measured with modern instruments, suggesting that prior estimates for maximum hurricane wave heights are too low, William Teague of the Naval Research Laboratory (NRL) at the Stennis Space Center in Mississippi and colleagues reported.
"Our results suggest that waves in excess of 90 feet are not rogue waves but actually are fairly common during hurricanes," Teague said in a telephone interview.
A wave that big would snap a ship in two or dwarf a 10-floor building, Teague said. And the sensors may have missed the largest waves, which the authors estimate had crest-to-trough wave heights exceeding 40 meters or 130 feet, the researchers said, reports Reuters.
According to Newsday, the giant wave did not reach land. Unlike a tsunami, which reaches down to the sea floor, this was a wind wave, generated on the ocean surface by the powerful forces of the storm.
Because shipping tends to try to avoid hurricanes, many large waves are unseen by humans, let alone measured.
Scientists at the National Oceanic and Atmospheric Administration have a different way of calculating wave heights, using buoys at sea.
Hendrik Tolman, an ocean wave expert at the NOAA's Climate Prediction Center, said a wave such as the giant one measured during Ivan is within expected limits.
Researchers generally focus on "significant wave height," which is the average of the highest one-third of waves, he said. Within that average, there can be much larger waves.
The highest significant wave height in Ivan was 52 feet as calculated by the NOAA buoys and 58 feet as calculated by Wang's group, of (NRL). In a short-lived storm such as Ivan, a maximum wave of twice the significant height can occur, said Tolman, who was not part of Wang's group.
Wang said Ivan's towering wave exceeds those measured in other fierce storms.
"In 1969, Hurricane Camille produced a 44-foot wave by an oil rig near the storm's center," he said. "Only two other buoy reports exceed the 52-foot mark set by Ivan, both of which occurred in the North Pacific where winter storms are larger than hurricanes," Wang said.
With forecasters expecting continued high hurricane activity in the next few years, this report should be a good starting point to increase wave-height research, Wang said.
On Tuesday, meteorologists at the National Weather Service increased their storm forecast for this year. There have already been eight named storms and they said there could be as many as 11 to 14 more tropical storms, including seven to nine more hurricanes, by the end of November.
Also, on Monday, Kerry Emmanuel of the Massachusetts Institute of Technology published a report indicating that global warming is making hurricanes stronger, informs the AP.
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