Application of surface-adjusted GOES low-level cloud-drift winds in the environment of Atlantic tropical cyclones. Part I: Methodology and validation

Beginning with the 1997 hurricane season, the Cooperative Institute for Meteorological Satellite Studies at the University of Wisconsin - Madison began demonstrating the derivation of real-time Geostationary Operational Environmental Satellite (GOES) low-level cloud-drift winds in the vicinity of Atlantic tropical cyclones. The winds are derived from tracking low-level clouds in sequential, high-resolution GOES visible channel imagery. Since then, these data have been provided to the National Oceanic and Atmospheric Administration (NOAA) Hurricane Research Division (HRD) for evaluation in their real-time tropical cyclone surface wind objective analyses (H*Wind) that are disseminated to forecasters at the NOAA National Hurricane Center on an experimental basis. These wind analyses are proving useful as guidance to support forecasters's tropical cyclone advisories and warnings. The GOES satellite wind observations often provide essential near-surface coverage in the outer radii of the tropical cyclone circulation where conventional in situ observations (e.g., ships and buoys) are frequently widely spaced or nonexistent and reconnaissance aircraft do not normally fly. The GOES low-level cloud-tracked winds are extrapolated to the surface using a planetary boundary layer model developed at HRD for hurricane environments. In this study, the unadjusted GOES winds are validated against wind profiles from the newly deployed global positioning system dropwindsondes, and the surface-adjusted winds are compared with collocated in situ surface measurements. The results show the ability of the GOES winds to provide valuable quantitative data in the periphery of tropical cyclones. It is also shown that the current scheme employed to extrapolate the winds to the surface results in small biases in both speed and direction. Nonlinear adjustments to account for these biases are presented.