The coupling between harbor seiches at Palawan Island and Sulu Sea internal solitons

Between 1989 and 1991 the authors made observations that confirm and elucid ate the coupling between harbor seiches at Puerto Princesa on Palawan Islan d in the Philippines and tide-generated internal solitons in the Sulu Sea. Published tidal current predictions for Basilan Strait in the Sulu Archipel igo were used to produce an index to the daily ebb tidal flows near Pearl B ank where the solitons originate. The coherence between predicted maximum e bb tidal current speed and observed seiche activity was 0.60 and the phase lag between the two quantities closely marched published estimates of the t ime required for solitons to cross the Sulu Sea. Arrival of the Sulu Sea wa ves immediately offshore of Puerto Princesa in the form of internal bores c orresponded in time to the initiation of harbor seiche activity. A more pre cise estimate of soliton travel time was determined from the time differenc e between predicted maximum ebb current and the initiation of seiche activi ty, and it was found to have a remarkably regular seasonal pattern, which c an be largely explained by seasonal variations in Sulu Sea temperature and salinity stratification. Therefore, the timing of seiche events at Puerto P rincesa can be forecast based on Sulu Archipeligo ride predictions and soli ton travel time. In general, the fortnightly pattern of seiche magnitude fo llows that of tidal current predictions, but day-to-day deviations are comm on. Seiche magnitude varies seasonally with generally low activity during t he winter (northeast) monsoon and usually maximum activity late in the summ er (southwest) monsoon.