A Lagrangian drifter array for targeted and sustained ocean observations of extreme waves and winds

Lagrangian drifters provide real-time ocean observations of surface waves, wind, and sea-level pressure to the Global Telecommunication System (GTS) for numerical weather forecasts and to improve situational awareness both along the coastline and in the open ocean. The drifters are part of a sustained array to monitor ocean currents, temperature, and sea-level pressure and are supplemented by air-deployable directional wave spectra drifters (DWSDs) and wind drifters (MiniMets) to monitor extreme events such as atmospheric rivers and tropical cyclones. From 2015-2023, hundreds of DWSDs were deployed to monitor extreme events across both the Pacific and Atlantic basins, with MiniMets selectively deployed under hurricanes. Here we show how these drifters adaptively sampled extreme events, providing valuable information in locations unsampled by coastal moorings. The DWSD can resolve the directional wave spectra in complex environments such as in the rear quadrants of tropical cyclones, where wind and waves may not be in the same direction. Surface wind observations from MiniMets can provide accurate directional information. These observations were compared to wave fields from global Wave Watch III (WW3), and to wind fields from the European Centre for Medium-Range Weather Forecasts (ECMWF) ERA-5, with noticeable mismatches in both the magnitude and sustainment of extreme events. The drifters can provide warning of extreme wave heights, and valuable observations to improve air-sea interaction parameterization in models.