A peek inside the eye of the storm
Saildrone vehicle allows meteorologists to study eyewall of hurricanes
WEST PALM BEACH, FLA.—There’s a slice of atmosphere where ocean meets sky that is a mystery to tropical meteorologists — a chaotic place where hurricane winds tear, 50-foot waves tower and evaporation feeds intensification.
But for the first time, messages from that frothy space were transmitted to scientists from the eyewall of a Category 4 cyclone by a specially equipped vessel floated into the path of hurricane Sam as it tore through the Atlantic basin last month.
Created by the California- based company Saildrone, the solar-powered, unmanned vehicle looks similar to a canoe but is self-righting with a leadweighted keel and a unique wing that helps with stabilization.
While the data collected by the drone in Sam’s eyewall was experimental and not used in forecasts by the National Hurricane Center, researchers see a potential to improve weather models with measurements including near-surface temperature, humidity levels, wave heights, wind speeds and ocean salinity.
The project is a partnership between the National Oceanic and Atmospheric Administration and Saildrone.
“Hurricanes are fuelled by the ocean through heat flux and we want to better understand the physical process happening in the air and sea interface,” said Jun Zhang, a meteorologist with NOAA’s Hurricane Research Division who worked on the experiment and flew missions into Hurricane Sam. “This process is one of the keys for hurricane intensification.”
Intensification, especially rapid intensification, remains a challenge for hurricane forecasters. Rapid intensification is defined as an increase in winds speeds of at least 56 km/h in 24 hours.
This hurricane season, six storms underwent a rapid intensification, including Sam, which accelerated from an 137km/h Category 1 storm at 5 p.m. Sept. 24 to a 225-km/h Category 4 by 5 p.m. the next day.
While hurricane track predictions have showed consistent improvement, intensity predictions stagnated through the 1970s, ’80s, ’90s and early 2000s. Some small improvements in intensity forecasting have been measured since 2013, according to a 2020 study in the journal of the American Meteorological Society.
Brian Connon, vice-president of ocean mapping for Saildrone, said sending the 23-foot long vehicles into a hurricane wasn’t something being considered by the company in 2014 when it was founded.
“We started primarily as ocean data collection to support science, but then NOAA came to us and asked if we could modify the design to survive in a hurricane,” Connon said. “We tested them last year in the North Pacific and that was when we said, yeah, we can do this.”
Five Saildrones have been operating in the Atlantic Ocean this year with two launched from Jacksonville, Fla., and three from the U.S. Virgin Islands. Operators — called mission managers — can manoeuvre the Saildrones from the company’s office in Alameda, Calif. They worked with NOAA to position the vessels in the path of storms and got close with Henri and Peter when they were tropical storms.
It wasn’t until Sam, which reached wind speeds of 240 km/h, that the Saildrone proved its grit, holding up in 50-foot waves.
Connon said the drone is aimed so that the wind is at its back.
In decades past, manned hurricane research missions into storms flew closer to the surface of the water. That was ultimately deemed too dangerous and now the lowest flights range between 8,000 and 10,000 feet depending if other hurricane flights are in the air, said NOAA flight meteorologist Nikki Hathaway.