(1) Event description: Figures 3i(1) and 3i(2) show the wind speed, direction, and wave height trends for this case. This 8-day event is classified as a "periodic event" due to its highly repetitive nature. Wind speeds and wave heights were moderate to (occasionally) high, overall. Wind directions were very consistently from the north-northwest (about 330 degrees), but tended to shift to the north during peak wind periods. Wind speeds on day 1 were light to moderate, no more than about 12 knots. Wave heights built steadily though, from 3 feet (initially) to 8 feet on day 1. Wind speeds on day 2 were slightly higher, averaging about 15 knots, while wave heights continued to rise slightly, up to about 9 feet. Beginning on day 3 and continuing through day 7, the wind and wave patterns were strongly diurnal in nature. Wind speeds were typically lowest, around 15 knots, in the late afternoon (about 00Z, or 1700 PDT). Wind speeds typically increased abruptly each evening, to between 22 and 27 knots, peaking about 3 to 6 hours later, around 03-06Z (2100-2400 PDT). In contrast to other events, which displayed a longer sustained rises in wind speed, the increases in this event were strongest over short periods, i.e. less than 6 hours. Maximum one-hour rates of rise were 11.4 knots, among the most rapid increases of any of the cases analyzed here. Each day showed progressively higher peak wind speeds, with an overall peak of 27 knots (peak gusts to 32 knots) on day 7.

Wave heights on days 3 through 7 followed a similar diurnal trend, driven primarily by the local winds. On day 3, wave heights peaked near 10 feet at very nearly the same time as the maximum wind. On days 4 through 7, wave heights continued to peak at about the same time as the winds, and were progressively (slightly) higher each day, with an overall peak for the event of 11.4 feet on day 7. After only a few hours (at most) near the peak, wave heights fell each day to about 7-8 feet, from early morning through afternoon.

(2) General Weather Situation: Figures 3i(3) through 3i(10) show the sea level pressure and upper air patterns for this event. Overall, the surface and upper air patterns showed little variation through the event. A weak upper trough persisted off the coast through the entire period, but intensified on days 7 and 8, as an upper low moved southeast near the British Columbia coast. At the surface, high pressure persisted over the northeast Pacific, with an associated ridge (of varying strength) extending into the Pacific Northwest, and a thermal trough just inland from the California coast. The event finally ended on day 8, as pressure gradients weakened due to a cold front approaching the Pacific Northwest.

(3) Harmonic Analysis of Wind Speed and Wave Height: Figures 3i(11) and 3i(12) show the harmonic analysis results for wind speed and wave height for this event. Overall, only about 6 percent of the variance in wind speed was explained by the first harmonic (period = 24 hours). This figure is (relatively) low, in part because of the overall increasing trends occurring on days 1 and 2, and also the decreasing trend on day 8. Limiting the harmonic analysis to days 2 through 7, which showed the strongest diurnal trends (time of maximum between about 10Z and 13Z), the overall percent-variance explained (first harmonic) increased to 23 percent. This figure would likely be even higher if the wind speed increases were not so strongly focused on a few hours each evening. Similarly, the percent-variance explained by the first harmonic on individual days appears deceptively low. Day 2 actually displayed the strongest percent-variance explained, about 81 percent. Days 3 through 7 ranged from 21 to 66 percent, but (again) these figures are lower because the stronger wind speeds are focused on only a few hours each evening. Harmonic analysis of the wave heights for this case showed similar results. Overall, only 5.6 percent of the variance was explained by the first harmonic. Similar to the wind speeds, this figure increased significantly (to 32 percent) when only days 2 through 7 were considered. Individual days ranged from 34 to 72 percent (all days), but as with the wind speeds, these figures would likely be higher if the daily wave height increases were no so narrowly focused on just a few hours each evening. Nevertheless, the wind and wave increases/decreases clearly followed a strong diurnal pattern.

(4) Pressure Gradients: Figure 3i(13) shows the pressure gradients for buoys #46022-46014 (22-14), #46027-46014 (27-14), and #46027-46022 (27-22), along with wind speeds at buoy #46014 for this case. It is not known why the 27-14 pressure gradients (i.e. absolute value of the differences) are smaller than the other two sets of gradients, given that the distance between buoys is greater. Perhaps there was a pressure sensor calibration error at one of the buoys. However, the trends in pressure gradients are more important (for purposes here) than the actual pressure values.

The 22-14 gradients tended to provide the best indication of wind speed increases, rising strongly (except for minor fluctuations) each day several hours before the initial wind increases. Further upstream, the 27-22 gradients also tended to increase prior to wind speeds, typically by about 6-8 hours. The 27-14 gradients, however, closely followed wind speed trends overall, thus providing little advance indication of increasing wind speeds. Regarding wind speed decreases at buoy #46014, the 27-22 pressure gradients seemed to provide the best indicator that wind speeds were near their peak, with the gradient peak typically occurring a few hours prior to the wind speed peak.

(5) Upstream Conditions: Wind speeds and wave heights upstream at buoy #46022 (110 miles north) were generally lower than at buoy #46014, averaging 9.1 knots (maximum 16.7 knots) and 5.2 feet (maximum 8.9 feet), respectively. At buoy #46014 during this period, wind speeds averaged 17.7 knots (maximum 27 knots) and wave heights averaged 7.9 feet (maximum 11.4 feet). Given the wave conditions at buoy #46022, about 2 feet of decay could reasonably be expected from the peak wave heights there, resulting in waves up to about 7 feet arriving at buoy #46014, which is consistent with observed conditions (daily minimum wave heights at #46014 were about 7-8 feet for all but the first and last days of the event).

Figure 3i(1). Wind speed and wave height, buoy #46014 (11-18 August 2000).

Figure 3i(2). Wind speed and direction, buoy #46014 (11-18 August 2000).


Figure 3i(3). Surface analysis (left) and upper air analysis (right), 11 August 2000.

Figure 3i(4). Same as Figure 3i(3), but for 12 August 2000.

Figure 3i(5). Same as Figure 3i(3), but for 13 August 2000.


Figure 3i(6). Same as Figure 3i(3), but for 14 August 2000.

Figure 3i(7). Same as Figure 3i(3), but for 15 August 2000.

Figure 3i(8). Same as Figure 3i(3), but for 16 August 2000.


Figure 3i(9). Same as Figure 3i(3), but for 17 August 2000.

Figure 3i(10). Same as Figure 3i(3), but for 18 August 2000.

Table 3i. Time of maximum amplitude and percent-variance explained by the first harmonic of wind speed and wave height, Case #9 (buoy #46014, 11-18 August 2000).

Figure 3i(11). Harmonic analysis of wind speed, buoy #46014 (11-18 August 2000).

Figure 3i(12). Harmonic analysis of wave heights, buoy #46014 (11-18 August 2000).

Figure 3i(13). Wind speed (buoy #46014) and pressure gradients (buoys #46027-46022, #46022-46014, and #46027-46014), 11-18 August 2000. Zero-values denote missing data (pressure gradients only).