Far below Hurricane Laura’s fury in the churning Gulf of Mexico, an array of underwater instruments have been taking the temperature of the ocean to measure the water’s heat content—a key factor that drives the intensity of hurricanes as they suck heat out of the ocean.

The instruments—known as Argo floats—measure water temperature and salinity as they bob from the Gulf’s surface to a depth of 2,000 meters and back up again. Earlier this week, Hurricane Laura traveled over a half-dozen of the floats as the storm zeroed in on the Texas and Louisiana coasts. Data from the floats are transmitted back to shore every five days, where they are fed into ocean models forecasters use to predict storm strength.