Underwater Glider Observations in the Caribbean Sea and tropical North Atlantic Ocean in Support of Tropical Cyclone Studies

An underwater glider operation is currently in place in order to provide sustained upper ocean environmental conditions in two areas of the eastern Caribbean Sea and tropical North Atlantic off Puerto Rico. The upper ocean density structure in this region has been linked to intensification and development of tropical cyclones, and to the seasonal Atlantic hurricane activity. The primary goal of this project is to assess the impact of tropical cyclone force winds on the temperature and salinity fields in the upper ocean and to evaluate the impact of these observations in tropical cyclone intensity forecasts. This is a multi-institutional effort that brings together the NOAA Atlantic Oceanographic and Meteorological Laboratory (NOAA/AOML), the University of Miami, the University of Puerto Rico Mayaguez, and the NOAA CariCOOs Regional Association, the U.S. Integrated Ocean Observing System (NOAA/IOOS), the Environmental Modeling Center (NOAA/EMC), and the National Data Buoy Center (NOAA/NDBC). This glider operations is providing up to 6,000 profile observations of temperature, salinity, and dissolved oxygen per year in areas that were very sparsely sampled during past decades All observations collected by this effort are made freely available in real-time. We present here results from the analysis of the observations obtained during the first mission, July-November 2014. During October 2014, Hurricane Gonzalo traveled within 85km from the location of an underwater glider situated north of Puerto Rico. Observations collected before, during, and after the passage of this hurricane were analyzed to gain better understanding of the upper-ocean response to hurricane winds. The main finding from our analysis is that low near surface salinity, probably linked to continental riverine input, potentially played an important role in changes observed in the upper-ocean; where a near-surface barrier-layer likely suppressed the hurricane-induced upper-ocean cooling, leading to smaller than expected temperature changes in the upper tens of meters of the ocean. Post-storm observations revealed a partial recovery of the ocean to pre-storm conditions 11 days after the passage of the hurricane. Comparison with a coupled ocean-atmosphere hurricane model, HYCOM-HWRF, indicates that model observations discrepancies largely resulted from the absence of this barrier layer in the initial ocean fields provided to the couple model. Observations and results presented in this work demonstrate the value of enhanced upper ocean observations, particularly provided by underwater gliders, for improving tropical cyclone intensity prediction and understanding the upper ocean response to the passage of a tropical cyclone.