La Jolla water temperature by month: what five years of observations show

Which La Jolla temperature are we analyzing?

This article uses the water-temperature series for NOAA station 9410230, La Jolla. The figures summarize the site's archived hourly observations for the five completed calendar years 2021–2025. They describe a particular instrument location; they do not establish the temperature of every cove, shallow surf zone or offshore depth around La Jolla.

La Jolla also has a separate scientific record maintained by Scripps. Its Shore Stations program measures surface and near-bottom water at Scripps Pier, with surface observations extending back to 1916. The program's station description distinguishes these two depths. We have not merged that daily research series with NOAA's hourly series, even though both are valuable ways to understand the local ocean.

Monthly averages and the range around them

The table pools qualifying hourly observations for each calendar month across 2021–2025. The middle range runs from the 10th to the 90th percentile: roughly the central 80% of those historical hourly values. It is neither the full minimum-to-maximum range nor an uncertainty interval around the mean. All five years qualify for every month here.

February has the lowest mean, 14.590°C to three decimals, narrowly below January's 14.622°C. Both display as 58.3°F after conversion and rounding. August has the highest mean, 20.019°C, producing a February-to-August difference of about 9.8°F (5.4°C). These are differences between pooled monthly means, rather than the annual temperature range of an individual year.

Sample counts also need a calendar interpretation. February has 3,382 observations here, compared with January's 3,714, primarily because February is shorter. Across these five years, including leap-year February 2024, there are 3,384 possible February hours. The two missing hours do not make February a poorly sampled month. Comparing coverage against possible hours is more informative than comparing raw monthly counts alone.

Source: Water Temperature Live analysis of NOAA CO-OPS station 9410230 hourly observations. UTC calendar months; each qualifying station-month-year requires at least 70% hourly coverage. Values rounded to one decimal after conversion; sample counts are unrounded.

The summer average hides the most useful detail

August's historical middle range is 7.3°C wide; February's is 1.9°C wide. That makes August's interval almost four times as wide in this dataset. A reading near 61°F and one near 73°F can therefore both fall inside August's historical middle range. Calling the month simply '68-degree water' removes information that matters when comparing a particular day with the recent seasonal background.

The table cannot tell us how much of that width comes from differences between years, changes within individual months or variation through the day. Those effects are pooled together. It also cannot identify the cause of a cold spell. NOAA's explanation of upwelling describes one relevant mechanism: displacement of surface water can bring colder subsurface water upward. Establishing that mechanism for a specific La Jolla event would require additional wind and ocean observations.

September stays close to August in this record

September's mean is 67.2°F, only about 0.8°F below August's 68.0°F. October then falls to 64.6°F, and November to 62.5°F. The observed seasonal pattern therefore does not end abruptly when the calendar turns from August to September. For a seasonal comparison, September belongs much closer to the summer peak than to the winter minimum.

This ordering describes the five-year aggregate, not a promise about any future September. The percentile intervals overlap substantially. A cold September episode can still be cooler than a warm October episode, and neither observation would overturn the average pattern. For a particular visit, the timestamped reading on the La Jolla conditions page answers a different, more immediate question.

Use the baseline as context, and keep the measurement identity

The most useful comparison is a recent observation against the range for the same calendar month and station. A value outside that range deserves attention as an unusually warm or cool reading relative to this reference period. It does not automatically indicate a faulty sensor: by construction, observations occur beyond the 10th and 90th percentiles.

Sampling methods matter when consulting another source. Scripps documents daily manual surface collection at approximately 0.5 meter, with a separate near-bottom procedure at the pier, in its field methods. Differences between a daily sample, an hourly instrument series and a satellite surface analysis should be investigated rather than averaged away. Our site methodology explains how current observations and seasonal context are labeled.