Climate and Average Weather Year Round in San Juan Puerto Rico
The climate in San Juan is hot, oppressive, windy, and partly cloudy. Over the course of the year, the temperature typically varies from 72°F to 89°F and is rarely below 69°F or above 91°F.
Based on the beach/pool score, the best time of year to visit San Juan for hot-weather activities is from early December to mid April.
Average Temperature in San Juan
The temperature in San Juan varies so little throughout the year that it is not entirely meaningful to discuss hot and cold seasons.
The figure below shows you a compact characterization of the entire year of hourly average temperatures. The horizontal axis is the day of the year, the vertical axis is the hour of the day, and the color is the average temperature for that hour and day.
Mombasa, Kenya (7,348 miles away) is the far-away foreign place with temperatures most similar to San Juan (view comparison).
In San Juan, the average percentage of the sky covered by clouds experiences extreme seasonal variation over the course of the year.
The clearer part of the year in San Juan begins around November 16 and lasts for 5.4 months, ending around April 30.
The clearest month of the year in San Juan is January, during which on average the sky is clear, mostly clear, or partly cloudy 81% of the time.
The cloudier part of the year begins around April 30 and lasts for 6.6 months, ending around November 16.
The cloudiest month of the year in San Juan is June, during which on average the sky is overcast or mostly cloudy 68% of the time.
A wet day is one with at least 0.04 inches of liquid or liquid-equivalent precipitation. The chance of wet days in San Juan varies significantly throughout the year.
The wetter season lasts 7.3 months, from April 24 to December 2, with a greater than 35% chance of a given day being a wet day. The month with the most wet days in San Juan is September, with an average of 14.8 days with at least 0.04 inches of precipitation.
The drier season lasts 4.7 months, from December 2 to April 24. The month with the fewest wet days in San Juan is January, with an average of 6.6 days with at least 0.04 inches of precipitation.
Among wet days, we distinguish between those that experience rain alone, snow alone, or a mixture of the two. The month with the most days of rain alone in San Juan is September, with an average of 14.8 days. Based on this categorization, the most common form of precipitation throughout the year is rain alone, with a peak probability of 50% on September 26.
To show variation within the months and not just the monthly totals, we show the rainfall accumulated over a sliding 31-day period centered around each day of the year. San Juan experiences significant seasonal variation in monthly rainfall.
Rain falls throughout the year in San Juan. The month with the most rain in San Juan is September, with an average rainfall of 4.7 inches.
The month with the least rain in San Juan is January, with an average rainfall of 1.3 inches.
The length of the day in San Juan varies over the course of the year. In 2023, the shortest day is December 21, with 11 hours, 1 minute of daylight; the longest day is June 21, with 13 hours, 14 minutes of daylight.
The earliest sunrise is at 5:47 AM on June 5, and the latest sunrise is 1 hour, 13 minutes later at 6:59 AM on January 19. The earliest sunset is at 5:46 PM on November 25, and the latest sunset is 1 hour, 19 minutes later at 7:05 PM on July 5.
Daylight saving time (DST) is not observed in San Juan during 2023.
The figure below presents a compact representation of the sun's elevation (the angle of the sun above the horizon) and azimuth (its compass bearing) for every hour of every day in the reporting period. The horizontal axis is the day of the year and the vertical axis is the hour of the day. For a given day and hour of that day, the background color indicates the azimuth of the sun at that moment. The black isolines are contours of constant solar elevation.
The figure below presents a compact representation of key lunar data for 2023. The horizontal axis is the day, the vertical axis is the hour of the day, and the colored areas indicate when the moon is above the horizon. The vertical gray bars (new Moons) and blue bars (full Moons) indicate key Moon phases.
We base the humidity comfort level on the dew point, as it determines whether perspiration will evaporate from the skin, thereby cooling the body. Lower dew points feel drier and higher dew points feel more humid. Unlike temperature, which typically varies significantly between night and day, dew point tends to change more slowly, so while the temperature may drop at night, a muggy day is typically followed by a muggy night.
San Juan experiences some seasonal variation in the perceived humidity.
The muggier period of the year lasts for 10 months, from March 26 to January 28, during which time the comfort level is muggy, oppressive, or miserable at least 86% of the time.
The month with the fewest muggy days in San Juan is February, with 23.5 days that are muggy or worse.
This section discusses the wide-area hourly average wind vector (speed and direction) at 10 meters above the ground. The wind experienced at any given location is highly dependent on local topography and other factors, and instantaneous wind speed and direction vary more widely than hourly averages.
The average hourly wind speed in San Juan experiences significant seasonal variation over the course of the year.
The windier part of the year lasts for 2.9 months, from June 4 to August 31, with average wind speeds of more than 10.9 miles per hour. The windiest month of the year in San Juan is July, with an average hourly wind speed of 12.4 miles per hour.
The calmer time of year lasts for 9.1 months, from August 31 to June 4. The calmest month of the year in San Juan is October, with an average hourly wind speed of 9.4 miles per hour.
The predominant average hourly wind direction in San Juan is from the east throughout the year.
San Juan is located near a large body of water (e.g., ocean, sea, or large lake). This section reports on the wide-area average surface temperature of that water.
The average water temperature experiences some seasonal variation over the course of the year.
The time of year with warmer water lasts for 3.3 months, from August 2 to November 12, with an average temperature above 83°F. The month of the year in San Juan with the warmest water is September, with an average temperature of 84°F.
The time of year with cooler water lasts for 3.3 months, from January 8 to April 16, with an average temperature below 80°F. The month of the year in San Juan with the coolest water is February, with an average temperature of 79°F.
Best Time of Year to Visit
To characterize how pleasant the weather is in San Juan throughout the year, we compute two travel scores.
The tourism score favors clear, rainless days with perceived temperatures between 65°F and 80°F. Based on this score, the best time of year to visit San Juan for general outdoor tourist activities is from late December to late March, with a peak score in the third week of January.
Tourism Score in San Juan
The beach/pool score favors clear, rainless days with perceived temperatures between 75°F and 90°F. Based on this score, the best time of year to visit San Juan for hot-weather activities is from early December to mid April, with a peak score in the second week of January.
Beach/Pool Score in San Juan
For each hour between 8:00 AM and 9:00 PM of each day in the analysis period (1980 to 2016), independent scores are computed for perceived temperature, cloud cover, and total precipitation. Those scores are combined into a single hourly composite score, which is then aggregated into days, averaged over all the years in the analysis period, and smoothed.
Our cloud cover score is 10 for fully clear skies, falling linearly to 9 for mostly clear skies, and to 1 for fully overcast skies.
Our precipitation score, which is based on the three-hour precipitation centered on the hour in question, is 10 for no precipitation, falling linearly to 9 for trace precipitation, and to 0 for 0.04 inches of precipitation or more.
Our tourism temperature score is 0 for perceived temperatures below 50°F, rising linearly to 9 for 65°F, to 10 for 75°F, falling linearly to 9 for 80°F, and to 1 for 90°F or hotter.
Our beach/pool temperature score is 0 for perceived temperatures below 65°F, rising linearly to 9 for 75°F, to 10 for 82°F, falling linearly to 9 for 90°F, and to 1 for 100°F or hotter.
Definitions of the growing season vary throughout the world, but for the purposes of this report, we define it as the longest continuous period of non-freezing temperatures (≥ 32°F) in the year (the calendar year in the Northern Hemisphere, or from July 1 until June 30 in the Southern Hemisphere).
Temperatures in San Juan are sufficiently warm year round that it is not entirely meaningful to discuss the growing season in these terms. We nevertheless include the chart below as an illustration of the distribution of temperatures experienced throughout the year.
Growing degree days are a measure of yearly heat accumulation used to predict plant and animal development, and defined as the integral of warmth above a base temperature, discarding any excess above a maximum temperature. In this report, we use a base of 50°F and a cap of 86°F.
This section discusses the total daily incident shortwave solar energy reaching the surface of the ground over a wide area, taking full account of seasonal variations in the length of the day, the elevation of the Sun above the horizon, and absorption by clouds and other atmospheric constituents. Shortwave radiation includes visible light and ultraviolet radiation.
The average daily incident shortwave solar energy experiences some seasonal variation over the course of the year.
The brighter period of the year lasts for 1.9 months, from March 7 to May 4, with an average daily incident shortwave energy per square meter above 6.6 kWh. The brightest month of the year in San Juan is April, with an average of 7.0 kWh.
The darker period of the year lasts for 3.9 months, from September 13 to January 9, with an average daily incident shortwave energy per square meter below 5.1 kWh. The darkest month of the year in San Juan is October, with an average of 4.6 kWh.
For the purposes of this report, the geographical coordinates of San Juan are 18.466 deg latitude, -66.106 deg longitude, and 36 ft elevation.
The topography within 2 miles of San Juan contains only modest variations in elevation, with a maximum elevation change of 194 feet and an average elevation above sea level of 5 feet. Within 10 miles contains only modest variations in elevation (984 feet). Within 50 miles contains very significant variations in elevation (4,390 feet).
The area within 2 miles of San Juan is covered by water (78%) and artificial surfaces (19%), within 10 miles by water (58%) and grassland (16%), and within 50 miles by water (75%) and trees (14%).
This report illustrates the typical weather in San Juan, based on a statistical analysis of historical hourly weather reports and model reconstructions from January 1, 1980 to December 31, 2016.
Temperature and Dew Point
There are 2 weather stations near enough to contribute to our estimation of the temperature and dew point in San Juan.
For each station, the records are corrected for the elevation difference between that station and San Juan according to the International Standard Atmosphere , and by the relative change present in the MERRA-2 satellite-era reanalysis between the two locations.
The estimated value at San Juan is computed as the weighted average of the individual contributions from each station, with weights proportional to the inverse of the distance between San Juan and a given station.
The stations contributing to this reconstruction are:
To get a sense of how much these sources agree with each other, you can view a comparison of San Juan and the stations that contribute to our estimates of its temperature history and climate. Please note that each source's contribution is adjusted for elevation and the relative change present in the MERRA-2 data.
All data relating to the Sun's position (e.g., sunrise and sunset) are computed using astronomical formulas from the book, Astronomical Algorithms 2nd Edition , by Jean Meeus.
All other weather data, including cloud cover, precipitation, wind speed and direction, and solar flux, come from NASA's MERRA-2 Modern-Era Retrospective Analysis . This reanalysis combines a variety of wide-area measurements in a state-of-the-art global meteorological model to reconstruct the hourly history of weather throughout the world on a 50-kilometer grid.
Land Use data comes from the Global Land Cover SHARE database , published by the Food and Agriculture Organization of the United Nations.
Elevation data comes from the Shuttle Radar Topography Mission (SRTM) , published by NASA's Jet Propulsion Laboratory.
Names, locations, and time zones of places and some airports come from the GeoNames Geographical Database .
Time zones for airports and weather stations are provided by AskGeo.com .
Maps are © OpenStreetMap contributors.
The information on this site is provided as is, without any assurances as to its accuracy or suitability for any purpose. Weather data is prone to errors, outages, and other defects. We assume no responsibility for any decisions made on the basis of the content presented on this site.
We draw particular cautious attention to our reliance on the MERRA-2 model-based reconstructions for a number of important data series. While having the tremendous advantages of temporal and spatial completeness, these reconstructions: (1) are based on computer models that may have model-based errors, (2) are coarsely sampled on a 50 km grid and are therefore unable to reconstruct the local variations of many microclimates, and (3) have particular difficulty with the weather in some coastal areas, especially small islands.
We further caution that our travel scores are only as good as the data that underpin them, that weather conditions at any given location and time are unpredictable and variable, and that the definition of the scores reflects a particular set of preferences that may not agree with those of any particular reader.
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