Evaluating HAFS with Hurricane-Penetrating Uncrewed Surface Vehicles and Other Components of the In situ Observing System

Saildrone uncrewed surface vehicles have demonstrated the ability to be navigated into hurricanes and collect continuous measurements of the air-sea transition zone. Measurements presently made available to forecasters and forecasting centers in near-real time from saildrones include near-surface wind speed and direction, barometric pressure, relative humidity, air temperature, ocean temperature, salinity, significant wave height, dominant wave period and ocean current speed and direction. These measurements complement those made from other components of the Atlantic hurricane observing system, especially platforms that measure other essential variables throughout the upper ocean and marine atmospheric boundary layer. In 2021, the current shear measured by a saildrone near the eyewall of Sam and the nearest (order 100 km) Argo profiles showed an initial trapping of wind momentum by a halocline in the upper 30 m, followed by entrainment of warmer subsurface water into the mixed layer. The Argo and saildrone measurements were used to identify biases in the ocean initial conditions provided to HWRF, and estimate the effects of these biases on the HWRF simulation of enthalpy flux in the eyewall. Multiple saildrone intercepts of hurricanes have occurred in each subsequent Atlantic hurricane season, including the 2022 saildrone intercept of Fiona, south of Puerto Rico, wherein a saildrone and seaglider where close to the TC center (order 10 km) and the 2023 intercept of Tammy, in which case saildrone measurements in the eye were coordinated with assets deployed from hurricane-penetrating aircraft, including a small unmanned aircraft system (sUAS). Here, we evaluate the performance of HAFS with measurements from coordinated in situ sampling, and a focus on using the saildrone and glider measurements in Fiona to understand the effect that biases in model track and salinity stratification have on the forecast system’s ability to simulate in-storm SST cooling and air-sea heat flux.