Saildrone Fleet to Intercept Hurricanes for Fifth Season
In partnership with NOAA, 10 Saildrone Explorer USVs will gather near-real-time data from inside extreme storms to improve rapid intensification forecasting and protect coastal communities.
The danger posed by a tropical cyclone is exceptionally severe when a storm undergoes rapid intensification, defined as an increase in maximum sustained wind speeds of at least 30 knots (35 mph) in 24 hours.
This process remains difficult for forecasters to predict, but the consequences can be dire. If a hurricane rapidly intensifies just before landfall, authorities have little time to prepare the public, thereby increasing the likelihood of severe damage to communities and loss of human life.
This year’s mission continues a multi-year collaboration between NOAA and Saildrone that began in 2021. NOAA scientists will define the operational objectives and provide mission tasking as tropical storms develop; Saildrone will operate and navigate the USVs to deliver in situ oceanographic and meteorological data in real time.
The Saildrone USVs will be strategically positioned in the western tropical/subtropical Atlantic Ocean, Caribbean Sea, and Gulf of America from August to November. As tropical cyclones develop, Saildrone mission operators will coordinate with NOAA to maneuver the USVs in and around the storms.
NOAA scientists at the Atlantic Oceanographic & Meteorological Laboratory (AOML) and the Pacific Marine Environmental Laboratory (PMEL) will use data to study how exchanges of heat, moisture, and momentum between the ocean and the atmosphere influence storm intensity.
Each Saildrone Explorer will be equipped with a suite of meteorological and oceanographic (metocean) sensors to measure wind speed and direction, air, surface, and sub-surface temperature, relative humidity, barometric pressure, salinity, and wave height and period. Additionally, two USVs will carry NOAA ASVCO2 sensors to measure the exchange of carbon dioxide between the ocean and the atmosphere. These observations will support NOAA’s hurricane research and modeling efforts.
Recent storms, including Hurricane Idalia in 2023, Hurricane Ian in 2022, and Hurricane Harvey in 2017, have rapidly intensified just before landfall, underscoring the need for better observations in the ocean regions where storms gain strength. NOAA aims to improve weather forecasting models, ensuring that state and local officials, and by extension the general public, receive longer lead times to prepare and evacuate accordingly.
Four years of intercepts and lessons learned
The Saildrone Explorer is a 7-meter (23-foot) USV designed to deliver continuous metocean observations across remote and extreme environments. The USVs used for the hurricane monitoring mission are equipped with a shorter, more robust “hurricane” wing, specially designed to withstand the conditions inside a tropical cyclone. Functioning similarly to a reefed sail on a sailboat, Saildrone engineered this wing to survive winds over 110 mph and towering waves exceeding 50 feet.
Saildrone has supported NOAA hurricane research across multiple seasons, deploying five USVs in 2021, seven in 2022, and 12 in both 2023 and 2024. Saildrone Explorers are multi-mission USVs, and several have been deployed on multiple hurricane missions; to date, 21 different USVs have been used in these missions. Since 2021, Saildrone has intercepted 21 named hurricanes and tropical storms on 46 occasions. In total, Explorer USVs have spent more than 2,600 days on mission supporting hurricane research. During each mission, Saildrone’s fleet has been co-located with NOAA’s aerial and sub-surface assets to form a comprehensive picture of the air and water column.
SD-1045, which set a Guinness World Record in 2021 for the highest wind speed measured by a USV, will deploy this year for its fourth hurricane mission. Data collected by SD-1045 during Hurricane Sam in 2021 indicated that surface salinity likely plays a role in the intensification process. Scientists believe that freshwater runoff from the Amazon River formed a barrier that prevented cooler, deeper water from mixing upward, allowing surface heat to continuously evaporate into energy and fueling the storm's intensification.
Saildrone’s efforts have also provided the only direct field observations of the ocean’s drag on hurricane winds, a phenomenon that is important to accurately represent in forecast models.
In 2024, Saildrone USVs intercepted hurricanes at different points around the eyewall. These were critical observations because the wind and ocean on different sides of the eye interact with the atmosphere differently. Specifically, on the right side of a storm, the winds and ocean waves move in the same direction, whereas on the left side, the winds and waves move in opposite directions. Scientists believe these complex dynamics regarding how the ocean and atmosphere exchange heat and momentum may also influence hurricane intensification.