Climate and Average Weather Year Round at Tristan Da Cunha St. HelenaAt Tristan Da Cunha, the summers are short, comfortable, windy, and mostly cloudy and the winters are long, cool, wet, extremely windy, and partly cloudy. Over the course of the year, the temperature typically varies from 51°F to 71°F and is rarely below 47°F or above 76°F. Based on the tourism score, the best time of year to visit Tristan Da Cunha for warm-weather activities is from late December to late March. Average Temperature at Tristan Da CunhaThe warm season lasts for 2.8 months, from December 30 to March 25, with an average daily high temperature above 69°F. The hottest month of the year at Tristan Da Cunha is February, with an average high of 71°F and low of 62°F. The cool season lasts for 4.1 months, from June 14 to October 18, with an average daily high temperature below 61°F. The coldest month of the year at Tristan Da Cunha is August, with an average low of 52°F and high of 58°F.
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. Santa Lucía, Spain (4,498 miles away) is the far-away foreign place with temperatures most similar to Tristan Da Cunha (view comparison). CloudsAt Tristan Da Cunha, the average percentage of the sky covered by clouds experiences mild seasonal variation over the course of the year. The clearer part of the year at Tristan Da Cunha begins around January 15 and lasts for 1.7 months, ending around March 6. The clearest month of the year at Tristan Da Cunha is February, during which on average the sky is clear, mostly clear, or partly cloudy 48% of the time. The cloudier part of the year begins around March 6 and lasts for 10 months, ending around January 15. The cloudiest month of the year at Tristan Da Cunha is June, during which on average the sky is overcast or mostly cloudy 62% of the time.
PrecipitationA wet day is one with at least 0.04 inches of liquid or liquid-equivalent precipitation. The chance of wet days at Tristan Da Cunha varies throughout the year. The wetter season lasts 8.3 months, from March 29 to December 5, with a greater than 34% chance of a given day being a wet day. The month with the most wet days at Tristan Da Cunha is June, with an average of 12.4 days with at least 0.04 inches of precipitation. The drier season lasts 3.7 months, from December 5 to March 29. The month with the fewest wet days at Tristan Da Cunha is February, with an average of 7.4 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 at Tristan Da Cunha is June, with an average of 12.4 days. Based on this categorization, the most common form of precipitation throughout the year is rain alone, with a peak probability of 44% on June 6.
RainfallTo 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. Tristan Da Cunha experiences significant seasonal variation in monthly rainfall. Rain falls throughout the year at Tristan Da Cunha. The month with the most rain at Tristan Da Cunha is June, with an average rainfall of 4.7 inches. The month with the least rain at Tristan Da Cunha is February, with an average rainfall of 2.4 inches.
SunThe length of the day at Tristan Da Cunha varies significantly over the course of the year. In 2024, the shortest day is June 20, with 9 hours, 37 minutes of daylight; the longest day is December 21, with 14 hours, 43 minutes of daylight.
The earliest sunrise is at 5:22 AM on December 6, and the latest sunrise is 2 hours, 41 minutes later at 8:03 AM on June 28. The earliest sunset is at 5:38 PM on June 12, and the latest sunset is 2 hours, 34 minutes later at 8:12 PM on January 5. Daylight saving time (DST) is not observed at Tristan Da Cunha during 2024. 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 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. 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. Tristan Da Cunha experiences some seasonal variation in the perceived humidity. The muggier period of the year lasts for 3.3 months, from January 3 to April 11, during which time the comfort level is muggy, oppressive, or miserable at least 5% of the time. The month with the most muggy days at Tristan Da Cunha is March, with 5.0 days that are muggy or worse. The least muggy day of the year is August 24, when muggy conditions are essentially unheard of.
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 at Tristan Da Cunha experiences significant seasonal variation over the course of the year. The windier part of the year lasts for 5.6 months, from April 21 to October 10, with average wind speeds of more than 17.0 miles per hour. The windiest month of the year at Tristan Da Cunha is July, with an average hourly wind speed of 19.9 miles per hour. The calmer time of year lasts for 6.4 months, from October 10 to April 21. The calmest month of the year at Tristan Da Cunha is February, with an average hourly wind speed of 14.2 miles per hour.
The predominant average hourly wind direction at Tristan Da Cunha is from the west throughout the year. Water TemperatureTristan Da Cunha 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 3.1 months, from January 14 to April 16, with an average temperature above 64°F. The month of the year at Tristan Da Cunha with the warmest water is February, with an average temperature of 66°F. The time of year with cooler water lasts for 4.0 months, from July 2 to November 1, with an average temperature below 58°F. The month of the year at Tristan Da Cunha with the coolest water is September, with an average temperature of 56°F.
Best Time of Year to VisitTo characterize how pleasant the weather is at Tristan Da Cunha 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 Tristan Da Cunha for general outdoor tourist activities is from late December to late March, with a peak score in the second week of February. Tourism Score at Tristan Da CunhaThe 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 Tristan Da Cunha for hot-weather activities is from mid January to late February, with a peak score in the second week of February. Beach/Pool Score at Tristan Da CunhaMethodologyFor 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. 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). Temperatures at Tristan Da Cunha 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. 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 experiences extreme seasonal variation over the course of the year. The brighter period of the year lasts for 3.4 months, from November 8 to February 19, with an average daily incident shortwave energy per square meter above 5.8 kWh. The brightest month of the year at Tristan Da Cunha is December, with an average of 6.7 kWh. The darker period of the year lasts for 3.8 months, from April 27 to August 20, with an average daily incident shortwave energy per square meter below 2.8 kWh. The darkest month of the year at Tristan Da Cunha is June, with an average of 1.8 kWh.
TopographyFor the purposes of this report, the geographical coordinates of Tristan Da Cunha are -37.050 deg latitude, -12.317 deg longitude, and 0 ft elevation. The topography within 2 miles of Tristan Da Cunha contains large variations in elevation, with a maximum elevation change of 2,231 feet and an average elevation above sea level of 48 feet. Within 10 miles contains large variations in elevation (6,647 feet). Within 50 miles also contains extreme variations in elevation (6,647 feet). The area within 2 miles of Tristan Da Cunha is covered by water (100%), within 10 miles by water (100%), and within 50 miles by water (100%). Data SourcesThis report illustrates the typical weather at Tristan Da Cunha, based on a statistical analysis of historical hourly weather reports and model reconstructions from January 1, 1980 to December 31, 2016. Temperature and Dew PointTristan Da Cunha has a weather station that reported reliably enough during the analysis period that we have included it in our network. When available, historical temperature and dew point measurements are taken directly from this weather station. These records are obtained from NOAA's Integrated Surface Hourly data set, falling back on ICAO METAR records as required. There are no other weather stations in our network within 200 kilometers of this location. Consequently, in the case of missing or erroneous measurements from this station, we fall back on NASA's MERRA-2 modern-era reanalysis , adjusted according to typical seasonal and diurnal differences between this station and the wide-area MERRA-2 reconstructed values.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. |