IOOS Hurricane Glider Coordination - The U.S. Integrated Ocean Observing System (IOOS)

Tropical cyclones are one of the costliest and deadliest natural hazards affecting the U.S. While NOAA has significantly improved hurricane track forecasts over the last few decades, intensity forecast improvements have lagged in comparison. Warm ocean waters provide the fuel for tropical cyclones and can have a major impact on their intensity. Unexpected rapid intensification of tropical cyclones in the hours before landfall can catch coastal communities off guard with deadly consequences, while unexpected rapid weakening can erode public trust in forecasts and evacuation guidance, and can lead to costly and unnecessary evacuations. Local governments and decision-makers need accurate hurricane forecasts to make cost-effective preparation and evacuation decisions that impact human life and property.

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Hurricane Gliders

Explore how coordinated glider observations help improve hurricane intensity forecasts.

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Accurate representation of the upper ocean in models is critical when forecasting hurricane intensity; however, there is a major shortage of subsurface ocean observations available to the models that are used for intensity forecasts. Underwater gliders are uniquely suited to fill this observing gap.

Gliders are one component of a suite of complementary observing platforms gathering critical data that help scientists understand and predict hurricanes. Collectively, these systems capture subsurface, air-sea interface, and atmospheric information to gain a full understanding and picture of the dynamics and processes affecting hurricane intensity and movement. These platforms include Argo floats, eXpendable BathyThermographs (XBTs), moored buoys, surface drifters, satellites, and high frequency radars.

Credit: NOAA/PMEL.

Gliders are used to continuously monitor and track ocean features that are linked to hurricane intensity changes. They can also capture how the ocean changes underneath a passing storm. Due to the gliders’ slow horizontal movement, they are not intended for chasing storms. Rather, they are best used for long-term sampling of these highly dynamic features throughout the entire hurricane season to help keep the global ocean models on track. Examples of these ocean features include:

Loop Current
Gulf Stream
Mid-Atlantic Cold Pool
Freshwater Barrier Layers
Atlantic Warm Pool
Eddies and Rings

Hurricane Katrina crossed over an area of high Tropical Cyclone Heat Potential, where a Loop Current Eddy contributed to rapid intensification just prior to landfall. Credit: NOAA/AOML.

All gliders measure water column temperature, salinity, and pressure, and may also contain additional sensors that measure chlorophyll, dissolved oxygen, currents, etc. These data are transmitted to the IOOS Glider Data Assembly Center (GDAC), from which the temperature and salinity data are delivered to the global ocean circulation models to "course correct" the simulations. The ocean models feed the hurricane models, and studies show that a realistic ocean used in the hurricane models helps produce a more accurate hurricane intensity forecast.

In 2014 the NOAA Atlantic Oceanographic and Meteorological Laboratory (AOML), along with partners including the Caribbean Coastal Ocean Observing System (CARICOOS) and Rutgers University, coordinated on the use of gliders to improve our understanding of the ocean's role in hurricane intensity changes. This collaboration expanded to include additional partners operating gliders in the Caribbean Sea and Tropical Atlantic, Mid-Atlantic Bight, South-Atlantic Bight, and the Gulf of America (formerly Gulf of Mexico). In 2018 the IOOS Office began coordinating this community of multi-institutional, multi-regional glider operators on glider missions during the Atlantic hurricane season.

Glider missions are primarily conducted in U.S. waters by IOOS Regional Associations and their academic members, the U.S. Navy, and NOAA Research partners. The glider operations also contribute to the NOAA Global Ocean and Monitoring Observations (GOMO) Extreme Events Program, which aims to coordinate complementary observing platforms (subsurface, surface and aerial) to improve our understanding of the role of the ocean, waves, and air-sea interactions in the development and intensification of hurricanes in order to produce more accurate and reliable models and forecasts.

By the Numbers

These metrics represent the Atlantic and Pacific hurricane seasons from 2018-2025:

Tropical cyclones measured: 38 of 49 (78%)
Major hurricanes aimed at U.S. waters: 12 of 13 (92%)

Glider deployments: 603
Glider days at sea: 27,701
Glider profiles: 936,168
Partner institutions: 27

References

Emanuel, K. Increasing destructiveness of tropical cyclones over the past 30 years. Nature 436, 686–688 (2005).
NOAA National Centers for Environmental Information (NCEI) U.S. Billion-Dollar Weather and Climate Disasters (2023). https://www.ncei.noaa.gov/access/billions/, DOI: 10.25921/stkw-7w73

Planned 2026 Hurricane Glider Missions

NOAA predicts a below-average Atlantic hurricane season and an above-average hurricane season for the Eastern Pacific and Central Pacific basins. The hurricane glider coordination group, composed of numerous organizations across NOAA, U.S. Navy, and academia, expects to deploy approximately 26 Atlantic and 6 Pacific hurricane mission-specific gliders, in hurricane-prone coastal regions of the U.S. Approximately 50 gliders deployed for other, non-hurricane missions will also be leveraged. The data from these gliders will be used in NOAA’s models to help improve the accuracy of hurricane intensity forecasts for the 2026 hurricane season

Planned 2026 Atlantic basin glider tracks identified by the hurricane glider partners, including the U.S. Navy, IOOS Regional Associations, NOAA/AOML, and other NOAA partners.

The planned hurricane tracks for gliders that will be deployed around the Island of Hawai’i and Guam during the 2026 Pacific hurricane season.

This map view shows important data for tracking storms and assessing coastal risks. Water temperature, wave height, and winds are loaded, as well as tropical cyclone outlook and active storms. Gliders provide data at their location. Click the "Explore Now" button for a real-time map view in the IOOS Model Viewer.

Model-Observation Comparisons

A team led by the Mid-Atlantic Regional Association Coastal Ocean Observing System (MARACOOS) at Rutgers University conducts qualitative comparisons between glider and Argo profile observations and global ocean model output to identify regions where models may benefit from additional observations or improved representation of ocean processes. Models included in the comparison are the NOAA Real-Time Ocean Forecast System (RTOFS), the U.S. Navy Earth System Prediction Capability (ESPC), the European Copernicus Marine Environmental Monitoring Service (CMEMS), and the East Coast Community Ocean Forecast System (ECCOFS). These analyses consistently show that modeled subsurface water mass properties in the upper 400 m of the water column improve in regions where glider and Argo profile observations are assimilated, while areas lacking subsurface observations tend to exhibit larger model biases. Results are communicated with the Office of Modeling and Development (OMD) within the NWS National Centers for Environmental Prediction (NCEP), and have directly informed improvements to the RTOFS model.

How to Access

Rutgers University has developed tools to explore these model-observation comparisons of ocean models and glider, Argo, and Fishing Vessel Observing Network (FVON) data. The IOOS Model Comparisons Archive Explorer features a quick-look panel that automatically loads the most recent available map for a selected region. Users can flip through regions, variables, depths, and model comparisons. The viewer also plots profiles from ocean models and in-situ observations for further analysis. An adaptive sampling guidance feature compares ocean heat content, sea surface salinity, and current speed from models in the Atlantic basin to help guide glider field operations. The Ocean Model Plotter allows along-track cross-section comparisons of observations and models.

Rutgers Archive Explorer comparing RTOFS and ESPC surface temperatures in the Caribbean. — Rutgers IOOS Model Comparisons Archive Explorer showing surface temperature comparisons of the NOAA Real-Time Ocean Forecast System (RTOFS) and Navy Earth System Prediction Capability (ESPC) models in the Caribbean.

Use Cases

Glider Data Reduces Model Biases Ahead of Hurricane Ernesto (2024)

A Bermuda Institute of Ocean Sciences (BIOS) glider, “Jack,” was deployed on August 12 shortly before Hurricane Ernesto approached the region. Prior to the deployment, RTOFS exhibited a warm and fresh bias relative to observed conditions. After the glider profiles were assimilated, the model showed improved agreement with observed temperature and salinity and produced a more accurate estimate of ocean heat content. Quantitative analysis showed a substantial reduction in bias and root mean square error (RMSE) in the upper 400 m of the water column following assimilation of the glider observations. Temperature bias decreased by approximately 110% and RMSE decreased by approximately 52%. Similar improvements were observed for salinity, with bias reduced by approximately 55% and RMSE reduced by approximately 64%. These results demonstrate the operational value of glider observations for improving the representation of upper-ocean conditions in ocean forecast models that support TC prediction.

Temperature and salinity profiles comparing glider Jack observations with RTOFS production and parallel models before and after assimilation during Hurricane Ernesto. — Qualitative comparisons of glider temperature and salinity observations and the global ocean models, NOAA RTOFS (production) and NOAA RTOFS Parallel (development version run in parallel), which was a development version of RTOFS. Before assimilation, the models are biased warm and fresh compared to the glider (upper left). After assimilation, the models improve their estimates of temperature and salinity which is more representative of the glider profile (upper right). The model’s production and parallel versions show a distinct convergence in ocean heat content (bottom). Source: Rutgers University

Ocean heat content estimates from RTOFS production and parallel models converge after assimilation of glider Jack observations. — Qualitative comparisons of glider temperature and salinity observations and the global ocean models, NOAA RTOFS (production) and NOAA RTOFS Parallel (development version run in parallel), which was a development version of RTOFS. Before assimilation, the models are biased warm and fresh compared to the glider (upper left). After assimilation, the models improve their estimates of temperature and salinity which is more representative of the glider profile (upper right). The model’s production and parallel versions show a distinct convergence in ocean heat content (bottom). Source: Rutgers University

Improvements to NOAA’s Real-Time Ocean Forecast System (RTOFS) ahead of Hurricane Melissa (2025)

In July 2025, RTOFS was upgraded to version 2.5, which included the application of a climatological constraint to the assimilation of sea surface height. This change addressed a subsurface negative salinity bias and cold temperature bias in the Subtropical Underwater in the Caribbean that was identified through the IOOS model-data comparisons. Following this upgrade, the ocean forecast ahead of Hurricane Melissa showed improved agreement with observed conditions in the Caribbean, despite the absence of gliders in the region at that time, although model temperatures at depth remained slightly cooler than observations.

Improved representation of the SubTropical UnderWater in the Caribbean after the implementation of RTOFS 2.5 Source: Rutgers University.

Since 2018, the U.S. Navy Commander, Naval Meteorology and Oceanography Command (CNMOC), and its operational command, the Naval Oceanographic Office (NAVOCEANO), has contributed Navy Littoral Battlespace Sensing gliders (LBS-G) to NOAA for ocean heat content missions. These Navy gliders have helped fill important upper ocean observing gaps in the NOAA ocean model that feeds the hurricane intensity forecasts. In fact, the Navy glider observations comprise approximately 25% of all the cumulative Atlantic glider observations delivered to NOAA each season. This partnership has involved over a dozen institutions and NOAA programs, working together on glider operations and data delivery. Since 2021, support for the glider operations has been made possible by the NOAA OMAO Uncrewed Systems Operations Center.