Summer Weather in Johannesburg Gauteng, South AfricaDaily high temperatures are around 77°F, rarely falling below 67°F or exceeding 85°F. The highest daily average high temperature is 78°F on January 1. Daily low temperatures are around 58°F, rarely falling below 51°F or exceeding 63°F. The highest daily average low temperature is 59°F on January 22. For reference, on January 1, the hottest day of the year, temperatures in Johannesburg typically range from 59°F to 78°F, while on July 4, the coldest day of the year, they range from 36°F to 61°F. The figure below shows you a compact characterization of the hourly average summer 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. Campo Quijano, Argentina (5,694 miles away) is the far-away foreign place with temperatures most similar to Johannesburg (view comparison). CloudsThe summer in Johannesburg experiences rapidly decreasing cloud cover, with the percentage of time that the sky is overcast or mostly cloudy decreasing from 37% to 24%. The clearest day of the summer is February 25, with clear, mostly clear, or partly cloudy conditions 76% of the time. For reference, on November 24, the cloudiest day of the year, the chance of overcast or mostly cloudy conditions is 38%, while on July 20, the clearest day of the year, the chance of clear, mostly clear, or partly cloudy skies is 92%. PrecipitationA wet day is one with at least 0.04 inches of liquid or liquid-equivalent precipitation. In Johannesburg, the chance of a wet day over the course of the summer is very rapidly decreasing, starting the season at 51% and ending it at 38%. For reference, the year's highest daily chance of a wet day is 55% on December 16, and its lowest chance is 1% on July 7. 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 summer in Johannesburg is decreasing, starting the season at 3.6 inches, when it rarely exceeds 6.3 inches or falls below 1.9 inches, and ending the season at 2.9 inches, when it rarely exceeds 5.3 inches or falls below 1.0 inches. The highest average 31-day accumulation is 3.9 inches on January 17. SunOver the course of the summer in Johannesburg, the length of the day is rapidly decreasing. From the start to the end of the season, the length of the day decreases by 1 hour, 1 minute, implying an average daily decrease of 41 seconds, and weekly decrease of 4 minutes, 50 seconds. The shortest day of the summer is February 28, with 12 hours, 38 minutes of daylight and the longest day is December 21, with 13 hours, 47 minutes of daylight. The earliest sunrise of the summer in Johannesburg is 5:07 AM on December 1 and the latest sunrise is 54 minutes later at 6:00 AM on February 28. The latest sunset is 7:05 PM on January 11 and the earliest sunset is 26 minutes earlier at 6:39 PM on February 28. Daylight saving time is not observed in Johannesburg during 2024. For reference, on December 21, the longest day of the year, the Sun rises at 5:12 AM and sets 13 hours, 47 minutes later, at 6:59 PM, while on June 20, the shortest day of the year, it rises at 6:54 AM and sets 10 hours, 30 minutes later, at 5:24 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 summer 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 Johannesburg is essentially constant during the summer, remaining within 1% of 1% throughout. The highest chance of a muggy day during the summer is 2% on February 23. For reference, on February 23, the muggiest day of the year, there are muggy conditions 2% of the time, while on April 12, the least muggy day of the year, there are muggy conditions 0% of the time. 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 Johannesburg is decreasing during the summer, decreasing from 8.0 miles per hour to 6.5 miles per hour over the course of the season. For reference, on September 24, the windiest day of the year, the daily average wind speed is 9.7 miles per hour, while on March 30, the calmest day of the year, the daily average wind speed is 6.4 miles per hour. The wind direction in Johannesburg during the summer is predominantly out of the north from December 1 to February 10 and the east from February 10 to February 28. 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 Johannesburg typically lasts for 9.9 months (301 days), from around August 4 to around June 2, rarely starting after September 5, or ending before May 11. The summer in Johannesburg is reliably fully within the growing 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 Johannesburg are very rapidly increasing during the summer, increasing by 1,552°F, from 1,524°F to 3,076°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 Johannesburg is essentially constant during the summer, remaining within 0.4 kWh of 7.3 kWh throughout. The highest average daily incident shortwave solar energy during the summer is 7.7 kWh on December 29. TopographyFor the purposes of this report, the geographical coordinates of Johannesburg are -26.202 deg latitude, 28.044 deg longitude, and 5,797 ft elevation. The topography within 2 miles of Johannesburg contains only modest variations in elevation, with a maximum elevation change of 440 feet and an average elevation above sea level of 5,705 feet. Within 10 miles contains only modest variations in elevation (1,230 feet). Within 50 miles contains very significant variations in elevation (2,851 feet). The area within 2 miles of Johannesburg is covered by artificial surfaces (99%), within 10 miles by artificial surfaces (76%) and grassland (17%), and within 50 miles by grassland (44%) and cropland (30%). Data SourcesThis report illustrates the typical weather in Johannesburg, 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 are 3 weather stations near enough to contribute to our estimation of the temperature and dew point in Johannesburg. For each station, the records are corrected for the elevation difference between that station and Johannesburg 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 Johannesburg is computed as the weighted average of the individual contributions from each station, with weights proportional to the inverse of the distance between Johannesburg 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 Johannesburg 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. 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. |