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How Underwater Robots Were Used to Help Improve Hurricane Forecasts in 2017

At a Glance

Autonomous gliders have provided temperature and salinity information since 2014.
This information is fed into computer models to enhance forecast accuracy.
The data bettered the forecast in at least two tropical systems in 2017.

Underwater hurricane hunting robots have been perusing the Atlantic and Caribbean with their target locked in on improving hurricane forecasts.

In 2017, at least three of these robots, called gliders, dove to 1,600 feet around 4,000 times to collect data directly under or very near four major hurricanes—Harvey, Irma, Jose, and Maria. This information, including crucial ocean temperature and salinity observations, is fed directly into hurricane intensity forecast models in near-real time.

Glider SG609 ready for deployment.
(Atlantic Oceanographic and Meteorological Laboratory/NOAA)

(MORE: 7 Reasons Why NOAA's New GOES-S Satellite is Important)

Data from the gliders showed that cool ocean temperatures likely had a role to play in the lack of intensification of Harvey and the weakening of Hurricane Jose in the eastern Caribbean and western Atlantic.

"The glider data provided valuable information on how storm force winds impact the ocean, and the potential impact of the ocean on hurricane intensification", according to NOAA.

Hurricane intensity remains one of the most challenging forecast obstacles, but recent upgrades and additions in technology like these gliders and GOES-16 and -17 hope to limit the amount of error in these forecasts.

The intensity of a hurricane can also have an impact on the future path of a hurricane. "Preliminary estimates are that the 2017 Atlantic track forecasts set record low errors at all time periods", according to the National Hurricane Center (NHC).

(MORE: Locations of the Gliders During the 2017 Hurricane Season)

The NHC goes on to recognize that a "significant reduction in [intensity] error has occurred in the current decade, which could mean that the recent investment in new models and techniques is beginning to pay off."

The latest computer model guidance is increasingly better at solving the relationship between the atmosphere and our oceans, likely with the help of data from these gliders.

How They Work and Additional Benefits

The gliders are autonomous underwater vehicles (AUV) that use small changes in buoyancy together with wings to propel itself forward. Due to their low energy consumption, the gliders can be monitoring the ocean for weeks or even months while racking up thousands of miles in distance. These vehicles are inherently safer than hurricane hunter aircraft since they are unmanned.

They are deployed by the R/V Sultana, a 42-foot research vessel owned and operated by the University of Puerto Rico - Mayaguez. Both students and researchers from the University of Puerto Rico and the University of Miami contribute to the program, including the remote piloting of the AUVs.

This glider information supplements information collected by Airborne eXpendable BathyThermographs (AXBTs), which are expendable probes deployed by the Hurricane Hunter planes into the ocean to measure temperature in the ocean along the plane's flight path.

(MORE: Six of the Most Harrowing Hurricane Hunter Flights in History)

The gliders are able to build a profile of ocean temperatures and salinity up to a depth of 3,300 feet. The upper portion of this layer is responsible for a large percentage of hurricane development and growth.

The warmer the water is under a hurricane and the deeper that warmth is, the more likely a hurricane is to intensify and for a more extended period of time.

Profile of ocean temperatures including observations taken by the glider (the vertical lines). The ocean's surface is located at the top of the image. The layer of water above the black line (79F) is warm enough to support hurricane growth.

The UAVs also study the salinity, or saltiness, of the ocean at depth. The reason for this? Salty water is usually buried deeper in the ocean than the warmer freshwater, but this all changes when a hurricane passes by. Freshwater and saltwater mix during a hurricane due to the intense wave action in the high winds, which brings salt water closer to the surface.

This saltwater is usually colder than the surface freshwater. When the cooler, salty water is mixed toward the surface, it can actually weaken hurricanes as they pass over the cooler wake of past hurricanes or their own cool wake in the case of slow-moving systems. Upwelled saltwater can also change or create new ocean currents that can change the intensity of hurricanes.

(MORE: When Hurricane Season Starts Early)

In addition, the gliders also provide information about chlorophyll concentration, which has been shown to have an impact on hurricane formation and growth. Chlorophyll is the green pigment that gives smaller organisms the opportunity to turn sunlight into food.

When chlorophyll levels are low, sunlight is able to penetrate into deeper levels of our oceans and thus leave the surface cooler than it would be with higher levels of chlorophyll. Varying levels of chlorophyll may actually be able to change the path of hurricanes as well.

The UAV's have been used by scientists since at least the 2014 Atlantic hurricane season.