Long-Range (5-10 Day) Swell Wave Forecasts
Abstract
Our long-term goal is to contribute to the accurate prediction of swell wave generation and propagation across ocean basins through the combined use of measurements and models. Our primary objectives are to develop methodologies to extract swell wave height and directional information from operational global wave models and use this data in concert with satellite and in situ measurements to make 5-10 day swell forecasts. A secondary objective is to use the resulting methods to contribute to future improvements in global wave model generation and long-distance propagation algorithms. The operational deep water wave forecasts model (WAM) presently used by Fleet Numerical provides wave forecasts (frequency-directional wave spectra) with a global resolution of 1 degree in latitude in longitude. The wave forecasts extend out to 5 days, which is the present forecast range of the input NOGAPS wind fields. However, it can take 10 days or more for generated swell waves to propagate across large ocean basins. Therefore, the global wave output contains additional long-range swell information in the form of long period wave energy that has been generated within the model along great circle paths that extend across large reaches of ocean. Our approach is to make long-range swell forecasts on a site-by-site basis. Great circle paths for all directions are traced from the forecast site to define its relationship to the global wave model output spectra as a function of wave frequency, direction, and time lag. Preliminary results from the long-range swell forecast model indicate that swell predictions can be extended out as far as 10 days without loss of model accuracy. In addition, the methodology can enhance the directional accuracy of WAM model forecasts through the direct use of great circles to propagate wave energy from distant source regions to the forecast site.
Document Details
- Document Type
- Technical Report
- Publication Date
- Jan 01, 1998
- Accession Number
- ADA551427
Entities
People
- Paul Wittmann
- R. T. Guza
- William C. O’reilly
- Y. L. Hsu
Organizations
- Naval Postgraduate School