San Francisco Ocean Water Hits 64 Degrees, Highest in Three Years Amid Broader Pacific Warming

San Francisco's ocean waters recorded a temperature of 64 degrees Fahrenheit on Sunday, marking the highest reading in three years. This unusual warmth, announced via a tweet from Tom Loverro, highlights a significant deviation from typical Northern California coastal conditions and contrasts sharply with the warmer summer ocean temperatures experienced on the U.S. Eastern Seaboard.

Historically, San Francisco Bay's average summer water temperatures typically range between 58 to 61 degrees Fahrenheit in August and September. The 64-degree measurement represents a notable increase above these averages, drawing attention to a broader marine heatwave affecting the Northeast Pacific.

Scientists attribute such elevated temperatures to phenomena like marine heatwaves and the weakening of the North Pacific High-pressure system, which normally drives winds that cool the ocean through evaporation and mixing. El Niño conditions can also contribute by reducing the upwelling of cold, nutrient-rich deep water along the California coast. This current heatwave is reportedly the fourth-largest in the northeast Pacific since 1982.

Warmer ocean temperatures pose significant threats to marine ecosystems. They can trigger harmful algal blooms, such as those producing domoic acid, which have led to illness and mortality in marine mammals like sea lions and dolphins. Such blooms can also force closures of commercial fisheries, including the lucrative Dungeness crab season, and compel marine species to alter their migratory patterns in search of cooler waters, disrupting established food webs.

The observed warmth in San Francisco stands in stark contrast to the expectations of many California natives, who are often surprised by the significantly warmer ocean temperatures found on the Eastern Seaboard. As Tom Loverro stated in his tweet:

“It’s funny because many CA natives are blown away when you tell them how warm the ocean is in the summer on the Eastern seaboard. They expect it to be colder than that!”

East Coast waters, influenced by currents like the Gulf Stream, commonly reach temperatures in the 70s or even 80s Fahrenheit during summer months, providing a stark thermal difference across the continental U.S. This persistent warmth on the East Coast is a key differentiator from the generally cooler Pacific waters off California.