San Juan weather in December
In December, San Juan has daytime highs averaging 28 °C, nights around 22 °C, with 13 wet days, and a sea temperature of 27 °C. Figures are 1991–2020 climate normals.
- 28.1°C Average high
- 22.1°C Average low
- 13days Wet days
- 49mm Rainfall
- 27.3°C Sea temperature
- 11h Daylight
Daily temperatures through December
How December 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 December | 28.2 °C | 22.4 °C | 44 % |
| 11–20 December | 28.1 °C | 22.1 °C | 38 % |
| 21–31 December | 28.0 °C | 21.9 °C | 40 % |
- Rain is most likely over days 1–10 of December (44 % of days) and least likely over days 11–20 (38 %).
What to expect
| Measure | Typical December | Share of the month |
|---|---|---|
| Days above 25 °C | 31 of 31 | 99 % |
| Days above 30 °C | 2.3 of 31 | 7 % |
| Days below 0 °C | 0 of 31 | 0 % |
| Days with more than 1 mm rain | 13 of 31 | 41 % |
Conditions in December
| Measure | Average |
|---|---|
| Mean temperature | 25 °C |
| Record high (1991–2020) | 32 °C |
| Record low (1991–2020) | 18 °C |
| Relative humidity | 82 % |
| Wind speed | 20 km/h |
| Cloud cover | 41 % |
Where San Juan ranks in December
| Ranking | Position | Value |
|---|---|---|
| The warmest places in North America in December | 27th of 50 | 28 °C |
December compared with the months around it
| Month | Avg high | Rainfall | Cloud |
|---|---|---|---|
| January | 27.9 °C | 43 mm | 38 % |
| February | 28.5 °C | 31 mm | 36 % |
| October | 30.3 °C | 113 mm | 58 % |
| November | 28.9 °C | 105 mm | 52 % |
| December | 28.1 °C | 49 mm | 41 % |
See all twelve months for San Juan
- December is the 11th warmest month here.
- It is the 4th driest month of the year.
- It ranks 4th for least cloud cover.
- Days last about 11 hours from sunrise to sunset.
- It rains on 13 of 31 days — 41 % of the month.
- Nights are about 6.0 °C cooler than the middle of the day.
- The hottest December day on record since 1991 reached 32 °C, 3.7 °C above the usual daytime high.
- Beach score: 78 / 100 — see how this is calculated.
QuestionsDecember in San Juan, answered
How warm is San Juan in December?
Daily highs average 28 °C and nights fall to about 22 °C, a spread of 6.0 °C between afternoon and dawn. That makes December the 10th warmest month of the year here.
Does it rain much in San Juan in December?
December averages 49 mm of rain, spread over about 13 of the 31 days — 41 % of the month. Cloud cover averages 41 % of the sky.
Is the sea warm enough to swim in December?
The sea averages 27 °C off San Juan in December. 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 December?
San Juan averages 11 hours between sunrise and sunset in December. 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.