On March 13, the Global Drifter Program (GDP) at AOML marked a milestone in its transition from Service Argos to Iridium for its array of surface drifting buoys: more than 50% of the array is now being tracked with the Iridium satellite system. The Iridium transition plan, announced by GDP principal investigators Rick Lumpkin (AOML) and Luca Centurioni (Scripps Institution of Oceanography) in November 2014, aims for the array to be 80% Iridium by mid-2019. Meeting this milestone will result in substantial cost savings for NOAA and faster access to data worldwide. Surface drifting buoys measure sea surface temperature and near-surface currents. The data are used in weather forecasts, seasonal to interannual climate predictions, and climate research.