San Juan weather in May
In May, San Juan has daytime highs averaging 30 °C, nights around 23 °C, with 16 wet days, and a sea temperature of 27 °C. Figures are 1991–2020 climate normals.
- 30.4°C Average high
- 23.4°C Average low
- 16days Wet days
- 108mm Rainfall
- 27.2°C Sea temperature
- 13h Daylight
Daily temperatures through May
How May develops
Averages for the first, middle and last part of the month, from daily 1991–2020 normals. Chance of rain is the share of years in which that calendar day recorded more than 1 mm.
| Days | Avg high | Avg low | Chance of rain |
|---|---|---|---|
| 1–10 May | 30.0 °C | 22.9 °C | 52 % |
| 11–20 May | 30.3 °C | 23.4 °C | 53 % |
| 21–31 May | 30.7 °C | 23.8 °C | 52 % |
What to expect
| Measure | Typical May | Share of the month |
|---|---|---|
| Days above 25 °C | 31 of 31 | 100 % |
| Days above 30 °C | 19 of 31 | 60 % |
| Days below 0 °C | 0 of 31 | 0 % |
| Days with more than 1 mm rain | 16 of 31 | 52 % |
Conditions in May
| Measure | Average |
|---|---|
| Mean temperature | 26 °C |
| Record high (1991–2020) | 35 °C |
| Record low (1991–2020) | 20 °C |
| Relative humidity | 79 % |
| Wind speed | 19 km/h |
| Cloud cover | 60 % |
May compared with the months around it
| Month | Avg high | Rainfall | Cloud |
|---|---|---|---|
| March | 29.3 °C | 41 mm | 39 % |
| April | 29.9 °C | 73 mm | 44 % |
| May | 30.4 °C | 108 mm | 60 % |
| June | 31.2 °C | 62 mm | 58 % |
| July | 31.4 °C | 68 mm | 54 % |
See all twelve months for San Juan
- May is the 5th warmest month here.
- It is the 10th driest month of the year.
- It ranks 11th for least cloud cover.
- Days last about 13 hours from sunrise to sunset.
- It rains on 16 of 31 days — 52 % of the month.
- Nights are about 7.0 °C cooler than the middle of the day.
- The hottest May day on record since 1991 reached 35 °C, 4.7 °C above the usual daytime high.
- Beach score: 70 / 100 — see how this is calculated.
QuestionsMay in San Juan, answered
How warm is San Juan in May?
Daily highs average 30 °C and nights fall to about 23 °C, a spread of 7.0 °C between afternoon and dawn. That makes May the 6th warmest month of the year here.
Does it rain much in San Juan in May?
May averages 108 mm of rain, spread over about 16 of the 31 days — 52 % of the month. Cloud cover averages 60 % of the sky.
Is the sea warm enough to swim in May?
The sea averages 27 °C off San Juan in May. Most people find water below 20 °C bracing and above 25 °C comfortable for a long swim; this figure is a monthly surface average, so a sheltered bay on a still afternoon can be warmer.
How long are the days in May?
San Juan averages 13 hours between sunrise and sunset in May. Day length is computed from latitude and date, so it is exact rather than modelled — but it says nothing about how much of that time is sunny.
Data sources and method
- ERA5 / ERA5-Land reanalysis — Copernicus Climate Change Service (C3S), ECMWF. Copernicus Licence
- Open-Meteo — Open-Meteo.com. CC BY 4.0
- NOAA OISST v2.1 — NOAA Physical Sciences Laboratory. Public domain
- GeoNames — GeoNames.org. CC BY 4.0
- Normal period
- 1991–2020
- Dataset version
- era5-1991-2020-scores1.1
- Last processed
Measured values come from ERA5 reanalysis and are reproduced unchanged. Calculated by us: daylight hours, beach and comfort scores, monthly rankings, threshold day counts, chance of a wet day by date, ten-day averages within the month. Full formulas are on the methodology page.
Contains modified Copernicus Climate Change Service information 2026. Neither the European Commission nor ECMWF is responsible for any use that may be made of the Copernicus information or data it contains.