A Remarkable Warming of Central California’s Coastal Ocean

A remarkable warming of Central California’s coastal ocean took place over the first three weeks of July. As of early July nearshore ocean temperatures were near or below long-term averages from Point Conception north to central Oregon (Figure 1, left panel).

Figure 1

Figure 1: Observed sea surface temperature (SST) on July 1 (left panel) and July 21 (right panel).

The warming was especially strong from July 15 to 23 (Figure 1, right panel), which coincided with a period when the region’s typically strong and persistent summertime northwesterly winds were very weak or absent (Figure 2). In addition to warming directly related to weaker winds, this greatly reduced coastal upwelling and allowed much warmer water that was offshore and to the south to move inshore and to the north. Coastal radar observations indicate very weak and even northward surface currents in the region of strong warming during this period. CTD measurements made during the SWFSC’s salmon trawl survey on the Tomales Bay and Pigeon Point survey lines indicated that the warm water extended to depths of 20 to 30 meters. The trawl survey also reported unusual encounters with ocean sunfish (Mola mola) inshore and sea nettles (Chrysaora fuscescens) farther north than they are typically encountered.

Figure 2: Daily average SST at a location near the outer Monterey Bay Buoy (46236) (from OISST.v2).

Figure 2

Figure 3: Observed 8-day average surface wind stress centered on the afternoon of July 20. Note the absence of vectors in the nearshore region of central California, and the broad region of poorly organized winds to the southwest.

Figure 3

More typical northwesterly winds and moderate coastal upwelling returned to the region on the afternoon of July 23 and persisted for 2 days (Figures 4 and 5), but in the past few days winds were relatively weak again. Observed ocean temperatures at the outer canyon of Monterey Bay (Buoy 46236) declined more than 2 °C from its peak on the afternoon of July 23 to mid-day July 25, but then increased again the next 3 days. At the time of this writing (July 28), nearshore SSTs remain from 2 to 3 °C above average along most of Central, Southern, and Baja California.

Figure 4: Daily geostrophic wind stress at 36N, 122W, for June and July 2014. Note the extended period of very weak wind stress from July 15-22. Figure from http://upwell.pfeg.noaa.gov

Figure 4

Figure 5: Daily Bakun Upwelling Index at 36N, 122W, for June and July 2014. Note the extended period of very weak upwelling from July 15-22, and the return of upwelling July 23-24. Figure from http://upwell.pfeg.noaa.gov

Figure 5

Learn more:

Unusual summertime warming off California Coast (September, 2014)

Contact: Nate Mantua (SWFSC Fisheries Ecology Division, Landscape Ecology Team)

July 29, 2014