The most significant information in this plot is the data for year 2006. This year was a La Niña year, when colder than average sea surface temperatures were found in the eastern equatorial Pacific and the Northern Pacific jet stream flow directed multiple storms to the northwest region of the U.S. As a result of this increase in the number of storms along the coast of Oregon during 2006, the frequency of high swell events was the highest of any year measured during this 10-year period for the 3 NDBC buoys near the coast.
The winter months of 1999 were dominated by a strong El Niño event when warmer than average sea surface temperatures in the equatorial eastern Pacific affected weather patterns along the western coast of the U.S. In recent years, evidence in the form of detailed equatorial buoy data has been recorded that shows anomalous upper level circulation during eastern Pacific El Niño years occasionally causes North Pacific jet stream flow to split during winter months. When this happens, compact but powerful low pressure systems may form beneath the southern split of the jet bringing unusually severe weather conditions to California. While the northern portion of the Northern Pacific jet stream is directed into Canada and Alaska when the jet stream
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splits. Therefore, during El Niño years the coast of Oregon may experience milder than average weather in the form of less rainfall and milder temperatures but may still have an increase in the average number of high swell events impacting the coastal areas as a result of the strong storms passing to the south of Oregon on route to the coast of California. The wave buoy data record for the winter months of 1998 / 1999 are an example of this scenario.
The analysis of 10 years of data from NDBC Buoys 46015, 46029 and 46050 (Figure 36) illustrates that a La Niña year such as 2006 can bring an increase in the frequency of high swell events to the coast of Oregon that are on par with, or greater than those caused by a strong El Niño event. The La Niña year of 2006 surpassed the El Niño year of 1999 having the most frequent number of high swell events in this 10-year period (1999 – 2008). This pattern is contrary to the 30-year data set from NDBC Buoy 46002 (Figure 36) were only El Niño years were identified as having the most significant impact on the frequency of high swell events reaching the coast of Oregon. Nevertheless, either of these two conditions, El Niño or La Niña, should be closely monitored when planning operations in the FERC permitted site areas along the coast of Oregon.
A detailed breakdown of the high swell events at each of the NDBC Buoys 46015, 46029 and 46050 which recorded the number of high swell events during each month shows that these events are largely confined to the winter months, October through April (Tables 19-21). There is only one occasion where one of these high swell events occurred during the month of May in 2005 and a high swell event was never recorded from June through September for the years of data analyzed. This detailed breakdown of the data to a monthly level demonstrates that periods of highest swells (storm events) are restricted to the winter months, and by comparison the summer months can be relatively calm. These tables also indicate the many months of missing data at each buoy, and this information should be carefully considered when viewing the overall totals for each wave buoy.