Hawaii wind and weather conditions derived from high resolution Sentinel-1 synthetic aperture radars

Justin E Stopa, University of Hawaii at Manoa, Ocean and Resources Engineering, Honolulu, HI, United States and Alexis Mouche, Ifremer, LOPS, Plouzané, France
The steep islands within the Hawaii archipelago create intricate wind patterns around the islands that have important impacts to the local weather conditions. For example, the Alenuihaha Channel in between the tall mountains (>3000 m) of Hawaii and Maui creates some of the strongest winds within the islands and micro-climates exist on the leeward side of Hawaii. In this study we use the synthetic aperture radar (SAR) sea surface backscatter from Sentinel-1 (S-1) dual platform mission to derive ocean winds at 1 km spatial scales near the Hawaii islands. Next we show that numerical models using the weather research (WRF) and forecasting model and scatterometer derived winds have discrepancies. The notable discrepancies are located in the channels, wake of the islands, and in coastal regions. We classify the ~2000 S-1A/B SAR acquisitions from 2014-2018 to create composite maps of the dominant local wind features. The majority of the acquisitions capture the steady Easterly trade winds and we resolve detailed features of the flow around the islands. We use the same wind classification to analyze the sea surface roughness. We observe rain, biology, and atmospheric features (wind streaks, fronts, convection) within the SAR backscatter. The SAR data is valuable resource than can help refine numerical weather models, improve the next generation of scatterometers, and understand mesoscale features especially in island chains like Hawaii that have localized weather conditions on land that are highly influenced by the surrounding ocean conditions.