Spring Weather in San Juan PeruDaily high temperatures are around 64°F, rarely falling below 59°F or exceeding 69°F. The highest daily average high temperature is 66°F on November 16. Daily low temperatures are around 38°F, rarely falling below 33°F or exceeding 44°F. For reference, on November 12, the hottest day of the year, temperatures in San Juan typically range from 40°F to 66°F, while on July 10, the coldest day of the year, they range from 34°F to 60°F. The figure below shows you a compact characterization of the hourly average spring temperatures. The horizontal axis is the day, the vertical axis is the hour of the day, and the color is the average temperature for that hour and day. La Ciudad, Mexico (3,403 miles away) is the far-away foreign place with temperatures most similar to San Juan (view comparison). CloudsThe spring in San Juan experiences very rapidly increasing cloud cover, with the percentage of time that the sky is overcast or mostly cloudy increasing from 32% to 68%. The clearest day of the spring is September 1, with clear, mostly clear, or partly cloudy conditions 68% of the time. For reference, on February 21, the cloudiest day of the year, the chance of overcast or mostly cloudy conditions is 83%, while on August 3, the clearest day of the year, the chance of clear, mostly clear, or partly cloudy skies is 72%. PrecipitationA wet day is one with at least 0.04 inches of liquid or liquid-equivalent precipitation. In San Juan, the chance of a wet day over the course of the spring is very rapidly increasing, starting the season at 1% and ending it at 13%. For reference, the year's highest daily chance of a wet day is 20% on January 27, and its lowest chance is 1% on June 5. RainfallTo show variation within the season and not just the monthly totals, we show the rainfall accumulated over a sliding 31-day period centered around each day. The average sliding 31-day rainfall during the spring in San Juan is increasing, starting the season at 0.1 inches, when it rarely exceeds 0.3 inches, and ending the season at 0.7 inches, when it rarely exceeds 1.9 inches. SunOver the course of the spring in San Juan, the length of the day is rapidly increasing. From the start to the end of the season, the length of the day increases by 1 hour, 6 minutes, implying an average daily increase of 44 seconds, and weekly increase of 5 minutes, 6 seconds. The shortest day of the spring is September 1, with 11 hours, 50 minutes of daylight and the longest day is November 30, with 12 hours, 56 minutes of daylight. The latest sunrise of the spring in San Juan is 6:01 AM on September 1 and the earliest sunrise is 44 minutes earlier at 5:17 AM on November 21. The earliest sunset is 5:51 PM on September 1 and the latest sunset is 22 minutes later at 6:13 PM on November 30. Daylight saving time is not observed in San Juan during 2024. For reference, on December 21, the longest day of the year, the Sun rises at 5:25 AM and sets 13 hours, 0 minutes later, at 6:25 PM, while on June 20, the shortest day of the year, it rises at 6:20 AM and sets 11 hours, 16 minutes later, at 5:36 PM. 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. MoonThe figure below presents a compact representation of key lunar data for the spring of 2024. 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. The label associated with each bar indicates the date and time that the phase is obtained, and the companion time labels indicate the rise and set times of the Moon for the nearest time interval in which the moon is above the horizon. HumidityWe 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. The chance that a given day will be muggy in San Juan is essentially constant during the spring, remaining around 0% throughout. WindThis 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 is gradually decreasing during the spring, decreasing from 7.0 miles per hour to 6.2 miles per hour over the course of the season. For reference, on July 30, the windiest day of the year, the daily average wind speed is 7.2 miles per hour, while on March 28, the calmest day of the year, the daily average wind speed is 5.6 miles per hour. The wind direction in San Juan during the spring is predominantly out of the north from September 1 to October 15, the west from October 15 to October 27, and the east from October 27 to November 30. Growing SeasonDefinitions 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). The growing season in San Juan typically lasts for 5.9 months (177 days), from around October 25 to around April 20, rarely starting before August 19 or after December 19, and rarely ending before February 22 or after June 3. The spring in San Juan is very likely fully outside of the growing season, with the chance that a given day is in the growing season very rapidly increasing from 20% to 80% over the course of the season. 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. The average accumulated growing degree days in San Juan are increasing during the spring, increasing by 340°F, from 160°F to 500°F, over the course of the season. Solar EnergyThis 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 in San Juan is gradually increasing during the spring, rising by 0.5 kWh, from 6.8 kWh to 7.3 kWh, over the course of the season. The highest average daily incident shortwave solar energy during the spring is 7.4 kWh on November 12. TopographyFor the purposes of this report, the geographical coordinates of San Juan are -14.650 deg latitude, -74.200 deg longitude, and 10,764 ft elevation. The topography within 2 miles of San Juan contains extreme variations in elevation, with a maximum elevation change of 4,423 feet and an average elevation above sea level of 10,879 feet. Within 10 miles also contains extreme variations in elevation (7,904 feet). Within 50 miles also contains extreme variations in elevation (15,758 feet). The area within 2 miles of San Juan is covered by shrubs (65%) and cropland (15%), within 10 miles by shrubs (42%) and grassland (16%), and within 50 miles by shrubs (28%) and bare soil (26%). Data SourcesThis 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 PointThere is only a single weather station, San Juan Airport, in our network suitable to be used as a proxy for the historical temperature and dew point records of San Juan. At a distance of 132 kilometers from San Juan, closer than our threshold of 150 kilometers, this station is deemed sufficiently nearby to be relied upon as our primary source for temperature and dew point records. The station records are corrected for the elevation difference between the 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. Please note that the station records themselves may additionally have been back-filled using other nearby stations or the MERRA-2 reanalysis. Other DataAll 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. DisclaimerThe 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. Please review our full terms contained on our Terms of Service page. |