The impact of QuikSCAT ocean surface vector wind retrievals in tropical cyclone analysis at the Tropical Prediction Center/National Hurricane Center

Remotely-sensed ocean surface vector wind (OSVW) retrievals from the SeaWinds scatterometer onboard the NASA QuikSCAT satellite have been an important source of data at the Tropical Prediction Center/National Hurricane Center (TPC/NHC) since 2000. These data fill a large void in surface wind information over the vast open oceans of the TPC/NHC areas of tropical cyclone analysis and forecast responsibility (the eastern North Pacific and Atlantic basins). QuikSCAT data have been utilized operationally for tropical cyclone center location/identification, intensity estimation, and analysis of outer wind field structure, especially when aircraft reconnaissance data are not available. The use of QuikSCAT by TPC/NHC Hurricane Specialists has increased during the past few years for each of these applications, all of which are important to the forecast and warning mission at TPC/NHC.

Manual analysis of all possible wind vector solutions from QuikSCAT (i.e., ambiguity analysis) is performed to assist in the identification or location of a tropical cyclone circulation center, particularly for weaker cyclones whose centers are often not easily discernible in geostationary satellite imagery. This information has been used to both initiate and discontinue advisories on a tropical cyclone, and it is often used to determine the initial location and motion of the tropical cyclone, which is a critical step in the forecast process, including for the initialization of model guidance.

QuikSCAT is also often used to help estimate the intensity of a tropical cyclone, particularly for tropical storms and marginal hurricanes. To quantify the accuracy of QuikSCAT in estimating intensity, we will present results from an evaluation of the maximum wind speeds, derived from near-real-time QuikSCAT retrievals at both 25-km and 12.5-km resolution over Atlantic tropical cyclones during 2005-07 and eastern North Pacific tropical cyclones during 2006-07, as compared to the final NHC best track intensities. Preliminary results indicate a large positive bias in QuikSCAT intensity estimates for tropical depressions, a smaller bias for tropical storms and category 1 hurricanes, and a large negative bias for category 2 and major hurricanes due to rain attenuation, resolution limitations, and saturation of the Ku-band signal.

Wind retrievals from QuikSCAT are often the only source of information on the structure of the outer wind field of a tropical cyclone that is far from land and outside the range of aircraft reconnaissance. QuikSCAT data are especially useful in this way for major hurricanes, for which the maximum radius of 34-kt winds often extends outside the region of heavy rainfall near the center of the cyclone.

Examples of the above applications will be presented, along with a summary of the limitations of QuikSCAT in tropical cyclone analysis. Finally, the need for next-generation OSVW satellite missions, based in part on experience gained with QuikSCAT and other sensors, will be briefly presented in the context of meeting operational requirements of the National Weather Service.