Use surface adjusted GOES low-level cloud-drift winds to improve the estimation of tropical cyclone outer wind radii

The Cooperative Institute for Meteorological Satellite Studies (CIMSS) at the University of Wisconsin-Madison provides real-time GOES low-level cloud-drift winds in the vicinity of tropical cyclones on a demonstrational basis to NOAA's Hurricane Research Division (HRD). The cloud-drift winds are derived from sequential high resolution GOES visible (VIS) channel imagery. These data were included in many of HRD's real-time tropical cyclone surface wind objective analyses which are sent to NOAA's Tropical Prediction Center (TPC) on an experimental basis during the 1997, 1998, and 1999 hurricane seasons. These wind analyses were used as guidance to support forecasters' tropical cyclone advisories and warnings. The satellite wind observations provide essential low-level coverage in the periphery of the tropical cyclone circulation where conventional in situ observations (e.g. ships, buoys, and Coastal-Marine Automated Network stations (C-MANs)) are often widely scattered or non-existent and reconnaissance aircraft do not fly. The GOES low-level VIS (GLLV) winds were extrapolated to the surface using a Planetary Boundary Layer model. These adjusted satellite data were used in real-time surface wind analyses and impact studies for 1998 hurricanes Bonnie, Danielle, Earl, and Georges as well as 1997 Hurricanes Danny and Erika and Tropical Storm Claudette. Datasets were also available for post-storm analysis in 1996 Hurricanes Erin and Opal and 1995 Hurricanes Edouard, Fran, and Lili and Tropical Storm Josephine. The satellite observations often helped to better define the spatial extent of the 34 kt surface wind radii and also redefined the 50 kt wind radii for some cases. Examples of the impact of these data on real-time tropical cyclone surface wind fields provided to TPC will be discussed, as will statistics on comparisons (300 cases) of the adjusted and unadjusted GLLV winds with in situ measurements.

The implementation of the new UW-CIMSS cloudbase height assignment algorithm for GLLV winds which was implemented prior to the onset of the 1999 hurricane season and its improvement over the old cloudtop height assignment algorithm will be discussed. In addition, the GLLV winds are validated against data from the new GPS dropwindsonde. Finally, the anticipated development cloud-drift satellite winds using the 4 micron shortwave infrared channel on the GOES imager will be discussed. This channel offers an increased ability (relative to the 11 micron longwave channel) to track low-level cumulus tracers in the periphery of tropical cyclones during nighttime observation. The potential for these shortwave infrared winds to complement the daytime observation of GLLV winds will be discussed.