Sustained and Targeted Ocean Observations for Improving Atlantic Tropical Cyclone Intensity and Hurricane Seasonal Forecasts

A pilot network of underwater gliders was implemented in 2014 by NOAA as part of a multi-institutional project to carry out sustained and targeted upper-ocean observations to 1000m depth in the Caribbean Sea and Tropical North Atlantic Ocean in order to enhance our knowledge on the role that the ocean plays in the intensification of TCs, and to assess the impact of these observations on the TC intensity forecast. During the first nine months of this project, over 4,800 temperature and salinity profiles were collected in areas off Puerto Rico where hurricanes are commonly observed and have been seen to intensify, and also where there were only 200 profile observations during the previous 10 years. Observations collected during this period include unique datasets of temperature and salinity conditions/changes under tropical cyclone winds for: (1) Tropical Storm Bertha (August 2014), and (2) Hurricane Gonzalo (October, 2014). During Hurricane Gonzalo, for the first time gliders were used to obtain ocean observations at a fixed location during the passage of a Atlantic hurricane, and along a repeat section to assess upper-ocean changes and recovery after the hurricane. Analysis of these observations revealed that salinity potentially played an important role in modulating the upper-ocean response to Hurricane Gonzalo. Comparison with model outputs from a coupled ocean-atmosphere hurricane model indicates that model observations discrepancies may be largely linked the observed salinity effects. These results may potentially lead to improvements in ocean simulations on the coupled model used for hurricane forecasts, which can ultimately bring benefits to the society by improving hurricane predictions. The observations collected by this project already emphasize the value of sustained and targeted ocean observations by underwater gliders for tropical cyclone intensification studies. Similar observations are expected to be performed during the following hurricane seasons, with the third NOAA mission currently underway.