Close Window

University of Washington: "Improving the prediction of topographically enhanced coastal winds in the eastern Gulf of Alaska"

Final Report

Locally intense coastal winds in the waters off Southeastern Alaska, in association with landfalling storms, have resulted in both the loss of lives and the sinking of vessels. Enhanced winds in this area can be caused by mesoscale pressure perturbations induced by the coastal terrain. The steady-state response to the imposed cross-terrain component of the flow is reasonably well understood. However, the response to time-dependent synoptic forcing is less straightforward. It appears that the strongest winds accompany trapped disturbances that propagate along the coast, but it is not clear exactly how these features are related to the properties of the incident flow. These features are not currently handled by operational numerical or conceptual forecast models, and these deficiencies can have tragic consequences, as recently exemplified by a fatal marine accident near Yakutat in October 1992. The accident occurred when the winds were two marine categories above the forecast, apparently due to an unforeseen mesoscale disturbance.

Progress in understanding these windstorms is hampered by the scarcity of analyzed cases. This project involves the following efforts:

1. Assemble case study source material and climatology into a comprehensive document.

2. Determine the prerequisite synoptic-scale conditions of these topographically enhanced coastal winds.

3. Identify the elements of the operational data base, including numerical guidance, satellite imagery, and real-time observations, that have predictive capability.

4. Develop conceptual and procedural methods for forecasting the subject windstorms in the operational environment.

5. Establish how forecasters can best utilize the observations that will become available from the WSR-88D radars being installed near Sitka and on Middleton Island.