2 Materials and Methods

2.1 CYGNSS

The CYGNSS constellation of 8 satellites collects GPS radar signals scattered on the forward (specular) direction to infer surface wind speeds, even through heavily precipitating clouds over the subtropical oceans (±38° latitude) (Ruf et al., 2019). CYGNSS surface wind speeds are used in conjunction with the ERA5 reanalysis to create an observational surface heat flux product (Crespo et al., 2019). We use CYGNSS Science Data Record (SDR) 2.0 flux data from August 2018 to December 2022. Our analysis is ocean-only. The fluxes are provided for specular points each of the 8 satellites observe at any given time. Preliminary assessment of CYGNSS Latent Heat Flux (LHF) accuracy against buoys in the tropical oceans indicates a slight positive bias of 38±35 Wm2 (Ruf et al., 2022), comparable to that of some more mature products (Bentamy et al., 2017).