San Diego record October heat and possible historic El Niño, Digi Mart USA News (San Diego): Record temperatures, heavy rain and extreme ocean conditions made October a historic month for San Diego. These phenomena may offer a preview of what is expected this winter: a possible historic El Niño event.
October 2026 began with extraordinary temperatures. The first week was the hottest start to October ever recorded in San Diego.
On October 3, temperatures reached 105°F at San Diego International Airport, the fifth-hottest day recorded there since record-keeping began in 1939.
The city also recorded several consecutive days above 100°F, which has happened only four times in its history. In addition, for the first time in October, San Diego experienced five consecutive days with temperatures of 90°F or higher.
At the end of the month, San Diego officially recorded its hottest October on record, with an average high temperature of 81.5 degrees. Perhaps even more surprising, the hottest October on record was also the sixth-wettest in the city’s history.
The city received 1.68 inches of rain, more than three times the October average of just half an inch. Measurable precipitation fell on seven different days, and the month ended with the second-wettest Halloween in San Diego’s history.
The combination of extremes is unusual for a city that typically experiences some of its driest and warmest weather in early autumn.
Records were not limited to temperature and precipitation. On October 29, La Jolla recorded the highest coastal water level in its history, reaching nearly eight feet above the station’s reference level.
The water rose enough that some San Diego coastal communities flooded.
The unusually high water level was caused by a combination of high tides and elevated sea levels. Part of the reason, according to the report, is that ocean water was unusually warm.
Warm water expands, raising sea level. Another factor is large underwater waves, known as Kelvin waves, that travel across the Pacific from the equator and move up the west coast.
These waves can raise sea level in coastal areas by six inches to one foot as they travel north along the shore. They are also closely linked to the development of a very strong El Niño event.
Another unusual effect of the warming ocean was visible to beachgoers. October also brought the clearest ocean water in more than a decade, with underwater visibility of 30 to 40 feet in some places.
Scientists at the Scripps Institution of Oceanography told NBC 7 that this clarity was mainly due to a scarcity of plankton in the water.
Normally, cold water rises from the deep ocean and carries nutrients that support plankton growth. However, unusually warm ocean conditions can inhibit this upwelling process, reducing the amount of nutrients and plankton near the surface.
The result is clear water that may look beautiful but could also signal changes in the marine ecosystem.
From the hottest October on record to unusually intense rain, record coastal water levels and significant changes beneath the ocean surface, San Diego experienced an extraordinary month of extreme phenomena.
Attention now turns to the winter. A potentially strong El Niño event is developing in the Pacific Ocean, with the possibility of becoming the strongest ever recorded.
Not all of October’s extreme events can be directly attributed to El Niño. However, during El Niño years the chances of above-normal rainy seasons increase.
In fact, four of the last five strong or very strong El Niño seasons recorded above-average precipitation in San Diego.
October has ended, but with a possible historic El Niño event on the horizon, it may only be the beginning of an extraordinary season for San Diego.
