Sustained Ocean Observations with Underwater Gliders in Support of Hurricane Intensity Forecasts

The main factors contributing to hurricane intensity changes include mid-level wind shear, interactions with topography, and enthalpy and momentum flux across the air-sea interface. The upper ocean thermal structure has been linked to hurricane intensification and weakening, through air-sea interaction processes that feed to the baroclinic processes in lower troposphere. Hence, incorrect-representation of the pre-storm thermal structure of the upper ocean may result in under or over estimation of air-sea fluxes and potentially, in turn, hurricane intensity change. Through the Disaster Relief Appropriations Supplemental funds, the National Oceanic and Atmospheric Administration (NOAA) leads a two year project with the participation of Integrated Ocean Observing System (IOOS) Regional Associations including MARACOOS, CARICOOS and SECOORA, Rutgers University, the University of Puerto Rico at Mayaguez, the University of Miami, and the University of Georgia, to provide real-time observations The project consists of the operation of underwater gliders, forming a picket line of instruments during the 2019 and 2020 Atlantic hurricane seasons in areas where hurricanes may rapidly develop. Initial outcomes from this effort include a substantial improvement of spatial coverage of subsurface observations in poorly sampled regions, and an assessment of the impact of subsurface ocean observations on hurricane intensity forecasts. When fully implemented, this effort, in addition to other ocean observational efforts, will support a dedicated pilot plan for ocean monitoring with the goal of improving hurricane intensity forecasts. This effort will be the next step in the transition of ocean monitoring from research to operations by supporting and combining resources, expertise, and regional and local knowledge. This particular plan intends to support several components of the operation of 15 to 20 gliders deployed in the Caribbean Sea, the tropical North Atlantic Ocean, and the Mid and South Atlantic Bights. The sampling strategy of observations was determined based on historic hurricane trajectories and areas of rapid intensification/weakening. Glider data are distributed in real-time through the IOOS Glider data assembly center and inserted into the Global Telecommunications System (GTS) for assimilation into operational forecast models worldwide. We present here analyses and results obtained with glider observations, which were the basis for the justification of this effort.