Using underwater autonomous vehicles called gliders, NOAA is now able to more accurately predict whether a tropical disturbance will intensify into a named storm. Gliders look like mini yellow submarines, but they are unmanned. Instead, they're preprogrammed remotely by computer. The gliders are deployed in the Atlantic Ocean and the Caribbean Sea to collect data on the water's temperature and salinity — two factors that are pivotal to the formation of hurricanes.
"Glider data are used daily and in real time for weather and hurricane forecasts," says Dr. Gustavo Goni, director of the Physical Oceanography Division at NOAA's Atlantic Oceanographic and Meteorological Laboratory (AOML). "Although there is no system now in the Atlantic Ocean, the data is being used and will continue to be used by the computer models during the whole hurricane season."
Ocean waters must be warmer than 79 degrees Fahrenheit for a hurricane to maintain its form. "Heat in the upper ocean is incredibly important to the intensification of hurricanes," Goni says. Scientists predict that climate change will lead to more severe hurricanes as global ocean temperature rises. Increases in greenhouse gasses have contributed to increased Atlantic hurricane activity since 1970, according to the Fourth National Climate Assessment.
As Hurricane Irma descended upon Florida in 2017, it traveled through warm waters of 86 degrees. That same year, Hurricane Maria was a tropical depression only three days before it made landfall on Dominica as a Category 5 hurricane. Maria's path through sea-surface temperatures of 84 degrees contributed to the storm's rapid intensification. Hurricane Wilma similarly traveled through ocean temperatures ranging from 82 to 85 degrees in 2005, according to NASA.
Saltwater is also a critical component of the escalation of hurricanes. It all comes down to density. Goni describes saltwater and freshwater like oil and vinegar — they're difficult to mix. The water underneath surface levels is much colder and saltier. But if the waters don't churn and mix, then surface-level water will remain heated. This allows storms, particularly slow-moving storms, to continue to draw energy and gain strength from the heated waters of the ocean surface.
This summer marks the fifth anniversary of NOAA's ocean glider project. Goni says scientists were discussing the desire for this type of study 50 years ago, but only within the past decade has the technology become advanced enough to make it possible. The program began with two gliders in 2014 but has quadrupled in scope in the past five years.
The submarine-like gliders can travel up to 20 kilometers daily, descending to a depth of up to 1,000 feet four times a day. They are about the height and weight of an average adult, and they're incredibly resilient. "They've been built for the open oceans and during harsh conditions," Goni says.
In the first year of the project, the gliders encountered Hurricane Gonzalo north of Puerto Rico. They've even survived shark attacks — Goni keeps a small jar in his office with the remnants of razor-sharp teeth recovered alongside the gliders.
There's still more work to be done, and Goni reiterates that the glider experiment is a project, not a program. "That's the exciting part," he says. "There are more unknown than known quantities."
A storm does not abide by borders, so the project is international in scope and nature. NOAA is the coordinating agency, but it also works with all regional associations affected by hurricanes. This summer, gliders are being launched off Florida Bay, the Bahamas, the Virgin Islands, the Dominican Republic, and Puerto Rico. The collaborative project ensures there's no duplication of efforts, but it also allows the scientists to help one another to rescue or repair a glider if it goes offline. Puerto Rico had no electricity and no running water a week after Hurricane Maria struck the island, but scientists there hopped on a boat and helped rescue a glider that had stopped responding. Goni says they've never lost a vehicle.
The data collected from the glider program will benefit hurricane models and weather forecasting systems to better inform people in harm's way. Long-term observations will contribute to a more accurate understanding of the role of the ocean in hurricane development.
"We as individuals benefit from science," Goni says.