El Niño Watch, Advisory 2007-08
Coastal Ocean Mean SST (°F) and Deviation from Normal, August, 2007
Several complementary images are now available:
SeaWiFS Chlorophyll a (view image) QuikSCAT Wind Stress Curl a (view image)
Regional Oceanic Conditions
Monthly mean sea surface temperature (SST) fields derived from NOAA satellites for August 2007 showed zonal (east-to-west) bands of negative and positive anomalies off the west coast of North America. These offshore patterns, which were similar to those that have been observed since May 2007, appear less extreme in August than in July 2007. Offshore, negative SST anomalies were observed north and south of the band of positive SST anomaly. Except for a small area between Point Conception (34°28'N) and Pigeon Point (37°N), positive coastal SST anomalies exceeding 2°C intensified during August north of Point Banda (32°N). Pacific-wide analyses show that areas of positive SST anomalies extended northward along the coast of Canada and Alaska and westward along the Alaska Peninsula and the Aleutian Island Chain. Negative SST anomalies below -2 °C were found south of Point Banda along the coast of Baja California, Mexico and in the lower Gulf of California (GOC). Offshore, positive SST anomalies surrounded a large area of negative SST anomaly (-1.0°C to -3.0 °C). This large area of negative SST anomaly occurred between 35°N and 52°N and from 135°W to 152°W. North of 35°N, this "donut-pattern" in the eastern north Pacific, was evident in the positive SST anomalies onshore and negative SST anomalies offshore. This anomaly pattern is characteristic of Aleutian Low atmospheric pressure system development that was anomalously strong relative to the subtropical high atmospheric pressure system (STH) to the south.
The August 2007 monthly mean wind and wind stress curl (WSC) patterns were very similar to the patterns observed in the July 2007 fields. Intermittent southward and southeastward winds along the coast produced positive on-to-offshore wind stress gradients and areas of strongly positive WSC, particularly in the Southern California Bight (33°N - 34°N), between Monterey Bay (36°N) and Point Reyes (38°N), north of Cape Mendocino (40°26'N) and near Cape Argo. In general, the monthly average winds east of 145°W and between 22°N and 51°N were mild. On the eastern side of the STH, the pressure gradient and consequent geostrophic winds were enhanced by interaction with continental low atmospheric pressure over northern Mexico, California and southern Oregon. The strength of this southeastward geostrophic wind enhancement is indicated by the SWFSC/ERD coastal upwelling index (UI). Positive UI indicated winds favorable to offshore transport and coastal upwelling from 24°N to 45°N, with negative anomalies, indicating weaker than average seasonal upwelling, from 30°N to 45°N. Positive UI anomalies were calculated from 30°N to 24°N, off Baja California. From 33°N to 39°N, UI calculations indicate that the UI was weaker than the seasonal average during June, July and August 2007. UI calculated from six-hourly pressure fields show that upwelling was episodic during August 2007. At 39°N the UI was strongly positive during four 3 - 4 day UI episodes during August. The UI episode that occurred at 39°N from the twenty-first through the twenty-third of August was particularly strong. From 27°N to 36°N, the six-hourly UI values showed strong diurnal variation and moderate upwelling.
In the August 2007 monthly composite surface Chlorophyll a (Chl a) images, near shore concentrations were similar to the patterns observed in throughout the summer. The coastal band of elevated Chl a concentration associated with lower SST and coastal upwelling (see above) was generally not as wide in July and August as in preceding months. Chl a concentrations exceeding 0.5 mg m-3 occurred in a 100-300 km wide coastal band over much of the coast from Santa Monica Bay (34°N) past the northern end of Vancouver Island (51°N). A narrow, 100 to 150 kilometer (km) wide, coastal band of elevated Chl a concentration was observed from the lower Southern California Bight (33°N) to the southern end of the Baja California Peninsula and southward along the coast of the Mexican mainland and along the coasts of the GOC. Chl a concentrations exceeding 10 mg m-3 were observed along the central California coast between Point Pinos (36°35'N) and Point Reyes (38°N), north of Cape Mendocino (40°26'N), in the vicinity of the benthic dead zone off Oregon and Washington, from the Columbia River mouth (46°N) to Cape Flattery (48°N) and along the coast of Vancouver Island. Several of the areas of elevated Chl a concentration were observed coincident with areas of strongly positive WSC. A persistent offshore area of elevated Chl a concentration, exceeding 5 mg m-3, was observed in an area of negative SST anomaly northwest of the 15°C SST isotherm. South of 45°N and southwest of the 18°C isotherm, Chl a concentrations were generally less than 0.2 - 0.3 mg m-3.
Equatorial Pacific Observations
During August 2007 the pattern of anomalous SST remained consistent with El Niño-Southern Oscillation (ENSO) neutral conditions in the tropical Pacific, with average to below-average SST extending from the date line to the west coast of South America. However, the tendency towards La Niña conditions (ENSO cool phase) continued as negative sea surface temperature (SST) anomalies in the eastern equatorial Pacific expanded westward. The upper-ocean heat content anomaly (average ocean temperature anomalies in the upper 300 meters of the ocean east of 180°) has persisted in a negative state since last February and became increasingly negative during July and August. The equatorial SST cold tongue from the east was well established with SST anomalies of about -2°C at the South American coast, where SST was less than 18°C, and anomaly of -1.0°C at 140°W, where the SST was less then 25°C. Sea surface height (SSH) anomalies of -5 to -10 centimeters (cm) were observed in the equatorial ocean between 110°W and 160°W and negative SSH anomalies less than -15 cm were found in the area around 11°N, 118°W. Large areas of the western tropical Pacific had positive SSH anomalies between 5 cm and 10 cm. SST exceeded 30°C over large expanses of the western tropical Pacific. Measurements at the end of August show negative temperature anomalies between the surface and 150 meters depth over large volumes of the eastern equatorial Pacific Ocean. Dynamic and statistical model results suggest a continued shift toward La Niña conditions as the year progresses.
Biological and Fisheries Observations
San Pedro (34°N) market squid (Loligo opalescens) landings in August 2007 were a meager 120 metric tons (mt), less than half the landings in August 2006, which was also a meager catch. Squid fishing took place off Santa Catalina Island (33°30'N). The average weight of sampled squid was 31 grams and the average mantle length was 11.4 cm. The average ex-vessel price $662/mt. Market squid were not landed in either the Monterey or the Port Hueneme areas during August 2007. The southern California sardine fishery, which had landed more than 50,000 mt by the end of July 2007, continued with more than 12,000 mt and 1,900 mt of sardines landed in Oregon and Washington, respectively, during August 2007. More than 20,000 mt of sardines have been landed by the northern sardine fishery during the 2007 season. By August 31, cumulative adult Chinook salmon counts at Bonneville Dam, on the Columbia River, were 60 percent of last year's equivalent cumulative counts and 46 percent of the ten year average counts; the return of sub-adult Chinook salmon was more than 200 percent of the 2006 cumulative sub-adult counts and more than the ten year average. Steelhead returns were slightly more than last year and the ten-year average at the Bonneville Dam fishway. Counts of coho salmon at Bonneville have been of similar magnitude to last year. Sockeye salmon counts at the Bonneville fishway have been 66 percent of last year and 40 percent of the ten-year average. Sockeye salmon counts on the Fraser River in southern Canada have also been lower than expected. At the Willamette Falls fishway, in northern Oregon, steelhead and adult chinook salmon cumulative counts have been 73 percent and 62 percent, respectively, of 2006 cumulative totals at the end of August. On the Rogue River, in southern Oregon, the summer steelhead run has been about 56 percent of the 2006 run, the lowest January to August cumulative returns since the 1998 - 2001. Rogue River summer chinook runs have been about the same for the last two years, with cumulative totals to the end of August about the same as for 1998 - 2001. Ocean sport fishing for chinook salmon has been similar to last year with intermittent poor to fair results on the Central California coast, but some of the fish landed were in the 20-30 pound (9-14 kilogram) range. However, some chinook salmon are traversing the Sacramento River and cumulative salmon counts at the Red Bluff Diversion Dam were about the same as last year's August totals, about 10 percent of numbers counted during 1999 - 2003. Coho salmon angling off northern Oregon has been productive with many anglers filling their limits of hatchery (healed adipose fin clipped) coho.
The Oregon recreational fishery was especially notable in that the albacore catch through August 31 was more than twice the previously recorded seasonal totals; albacore were located as close as 20 km offshore. In August, barracuda, yellowtail and bonito were available to recreational anglers within a day's trip off San Diego (32°40'N). During August, recreational anglers going offshore were taking albacore and an occasional Mahi Mahi all along the length of California and off southern Oregon. Yellowfin tuna have been available to recreational anglers offshore to the southwest of San Diego. Humpback whales continued to be common along the Central California coast. Blue whales were encountered along the central and southern California coasts.