The climate of Los Órganos: 45 years of sea and air data

Published 31 October 2026

The data and their limits

Water temperature comes from NOAA's OISST v2.1, which blends satellites, ships, buoys and Argo floats into a global 0.25° grid with daily data since 1 September 1981^1,2. We use the cell nearest Los Órganos that is sea, centred at 4.125° S and 81.125° W: a square about 28 km across whose centre is about 6 km from the town. It is the mean temperature of that square, not of a dive site.

Air, rain and wind come from NASA POWER, which takes them from the MERRA-2 reanalysis on a grid of ½° of latitude by ⅝° of longitude, about 55 by 70 km^3,4. A reanalysis is a weather model corrected with observations⁴, and its cell mixes sea, beach and dry land: it describes the area, it is not a weather station. So we read its rain as an order of magnitude and to compare years with each other, not to the millimetre.

For El Niño we use two NOAA indices. Niño 1+2 is the sea temperature in the box from 0° to 10° S and 90° to 80° W, off Ecuador and northern Peru, computed from OISST as the difference from the 1991–2020 mean^5,6. The ONI is the three-month mean of the Niño 3.4 region in the central Pacific, NOAA's historical index for El Niño and La Niña; since 2026 its official monitoring uses the RONI, a relative version of the same index⁷.

Everything is measured at the surface. Below it the water cools with depth, and the layer where it changes fast is called the thermocline⁸: when diving you can meet water colder than these figures. The typical year is computed over 1991–2020, the 30-year period of the World Meteorological Organization's most recent climatological normals⁹.

The water's typical year

In 1991–2020, the sea surface off Los Órganos averaged 22.8 °C over the year¹. The warmest month is February, at 24.9 °C on average (March, almost the same), and the coldest August, at 21.2 °C¹.

A month is not the same every year. In eight Februarys out of ten, the month's mean fell between 23.9 and 26.0 °C; in eight Augusts out of ten, between 19.9 and 22.1 °C¹. In August, the surface was below 20 °C on 20 % of the days of 1991–2020; from January to March, almost never¹.

The warmest day on record was 23 March 1998, at 30.0 °C, during the 1997–98 El Niño; the coldest, 29 July 2012, at 16.8 °C¹.

The air follows the sea. Its mean runs from 20.9 °C in August to 25.1 °C in February, and the mean daily maximum in February is 26.8 °C³.

Rain and wind

It rains little and almost only in summer. In 1991–2020 an average of 249 mm fell per year, and 86 % of it from January to April³. The wettest month is March³.

The mean is misleading, because a few very wet years push it up. In March the mean rain is 90 mm, but the median is 43 mm: half of all Marchs got less than that³. The December-to-April season of a typical year (the 1991–2020 median) adds up to 122 mm³.

The wind blows from the south-southwest and is lightest in March, at 3.6 m/s on average (13 km/h), and strongest in October, at 6.6 m/s (24 km/h), 10 m above the ground³. From June to November the monthly mean is above 6 m/s³.

Is the sea getting warmer?

To measure the trend we removed the seasonal cycle (each month minus its 1991–2020 mean), averaged each complete year and used two methods that one extreme year cannot drag along: Sen's slope and the Mann–Kendall test^10,11. Because a warm year tends to follow another, the test is corrected for that autocorrelation¹².

Surface water temperature changed by +0.30 °C per decade between 1982 and 2025 (95 % interval: +0.13 to +0.47; p = 0.003)¹. The trend is statistically significant. Over the 44 years of the record that is about 1.3 °C.

Air temperature in the POWER cell changed by +0.15 °C per decade between 1981 and 2025 (95 % interval: 0.00 to +0.28; p = 0.048)³. It is statistically significant, but only just: the interval nearly reaches zero. Annual rain changed by +31 mm per decade between 1981 and 2025 (95 % interval: −3 to +56; p = 0.068)³. It is not statistically significant: these data cannot rule out no change at all.

A 44-year trend in a cell by the coast is not a projection. El Niño moves more in a single year than the trend moves in a decade: the monthly water anomaly reached +5.6 °C in June 1983 and fell to −3.1 °C in March 1986¹.

El Niño rules

Month by month, the water anomaly off Los Órganos follows that of the Niño 1+2 region closely: their correlation is r = 0.76 over 537 months^1,6. With the ONI, which watches the central Pacific, it is weaker, r = 0.41⁷. The water here answers mostly to what happens off the coast; in part it is the same water, because the Los Órganos cell lies inside the Niño 1+2 box.

Rain follows El Niño too, though less closely than the water. Between 1983 and 2026, December-to-April rain rises with the Niño 1+2 anomaly of those same months (Spearman rank correlation ρ = 0.58, 44 seasons)^3,6. In Piura, warm sea near the coast during El Niño can bring very heavy rain¹³.

In 1982–83, the water anomaly reached +5.6 °C in June 1983, and the 1983 rainy season added up to 491 mm, 4.0 times the median^1,3. In 1997–98, the water anomaly reached +4.8 °C in May 1998, and the 1998 rainy season added up to 1685 mm, 13.8 times the median: the wettest season on record^1,3. Takahashi studied the extreme rains of Piura in 1997–1998 and links them to very strong El Niño conditions¹³.

2017 was a coastal El Niño: a rapid warming of the eastern Pacific early in the year, with almost no warning, which brought torrential rain to Peru and Ecuador and developed differently from central and eastern Pacific El Niños¹⁴. Here the water anomaly reached +3.2 °C in March 2017, and the 2017 rainy season added up to 760 mm, 6.2 times the median^1,3. In 2023, the water anomaly reached +4.2 °C in April 2023, and the 2023 rainy season added up to 450 mm, 3.7 times the median^1,3.

As we write, the sea is warm again. In September 2026 the cell's water anomaly was +4.7 °C and Niño 1+2's +4.7 °C, and the July–September 2026 ONI reached +2.2 °C^1,6,7. What the 2027 rainy season will bring is not in these data yet.

What it means if you come to dive

From January to April the surface water is the warmest of the year, with means from 23.5 to 24.9 °C; from July to October it is the coldest, with means from 21.2 to 21.8 °C¹. Those cold months are also the windiest³.

It can be colder below than these figures, because the water cools with depth⁸. We found no source we can cite for which wetsuit thickness goes with which temperature, so we give no table: if in doubt, ask us what we wear that month.

In an El Niño year the water can be several degrees warmer than the mean and the rain can multiply^1,3. If you travel from January to April in such a year, follow the official warnings before you set out.

How we computed it

A program of ours downloads the data, keeps them exactly as they arrive and always runs the same arithmetic on that copy. From OISST's daily data, a month's mean is computed only when all its days are present. Compared with the monthly means NOAA itself publishes for the same cell, they agree to a thousandth of a degree¹. A month's rain is the sum of its days, and its wind the mean of its days³.

The 10th and 90th percentiles are those of the 1991–2020 monthly means: eight years in ten fall between them. Trends use Sen's slope, with its 95 % interval, and the Mann–Kendall test with its variance corrected for the lag-one autocorrelation of the detrended series^10,11,12. As a check, Sen's slope over the 541 monthly anomalies gives +0.32 °C per decade¹.

Correlations with El Niño are Pearson's on monthly anomalies and, for rain, Spearman's rank correlation, because one very wet year weighs too much in a linear one. Consecutive months are not independent, so we read those correlations as a measure of likeness and give them no p-value. We recomputed the main figures another way (NOAA's monthly means and SciPy's statistical functions) and they agree.

The data run to 30 October 2026 (water) and 28 October 2026 (air, rain and wind); the arithmetic uses complete months up to September 2026.

Data credits

Sea temperature: NOAA OISST v2.1, from NOAA NCEI, served by NOAA PSL.^1,2 El Niño indices: NOAA Climate Prediction Center.^6,7

Air, rain and wind, with the acknowledgement and the data reference the POWER project asks for: The data was obtained from National Aeronautics and Space Administration (NASA) Langley Research Center's Prediction Of Worldwide Energy Resources (POWER) project funded through the NASA Earth Science Division. The data was obtained from the POWER Project's Daily 2.10.1 version on 2026/10/31.³