GFS-based MOS wind forecast guidance for islands in the tropical western Pacific Ocean

The Meteorological Development Laboratory (MDL) has established a Model Output Statistics (MOS) system which provides objective weather forecast guidance for NWS forecasters. This guidance contains forecasts of numerous meteorological elements for the contiguous United States (CONUS), Alaska, Hawaii, and Puerto Rico. Until now, MOS guidance for islands located in the tropical western Pacific Ocean has been unavailable for any meteorological element. New MOS guidance has now been developed for islands located in the area from 15° S to 30° N and from 130° E to 170° W. This new guidance also provides forecasts for a station in the Southern Hemisphere, which is unique among the MDL MOS guidance packages. While the development of forecast guidance is planned for several meteorological elements that are essential and required by the NWS Pacific Region, only wind prediction equations have been developed at this time.

The new tropical western Pacific MOS system is based on the model output of the Global Forecast System (GFS). The wind forecast guidance was developed for 15 stations and is scheduled for implementation during early 2005. The guidance for two stations in the Western Hemisphere will be added to the existing Hawaii MOS guidance and will be operational in April 2005, and that for 13 stations in the Eastern Hemisphere will be operational as a stand-alone MOS package in June 2005.

Archives of GFS model output and hourly data for April 2000 through September 2004 were used in the development of this guidance. The data were stratified into dry (October through May) and monsoon (June through September) seasons prior to equation development. Investigation of the MOS wind forecast equations showed that predictors in a shallow layer near the Earth's surface predominated for the dry season whereas predictors in the lower and mid-troposphere (from the surface to 500 mb) were important for the monsoon season. In a test on independent data, the MOS wind forecasts were compared with the GFS model output wind direction and speed. The mean absolute errors of the MOS wind speed forecasts were about half that of the GFS model. The MOS guidance also predicted wind directions better than the GFS model, especially for strong winds (speed = 10 kts). This presentation focuses on the improvement of the MOS wind guidance over the GFS forecasts, and development of additional weather guidance for the western Pacific Ocean.