May - September. These summer months are the best time to go to Svalbard. This is the warmest time to visit, and most suited to some of the outdoor activities you can enjoy such as snowmobile tours, skiing, dog sledding, hiking, and boat tours.
https://www.naturalworldsafaris.com/polar-regions/svalbard/when-to-go
Climate and daylight in Svalbard. Climate. Svalbard has an Arctic climate tempered by the warm North Atlantic Current, with average summer temperatures ranging from 4 to 6 °C (39.2 to 42.8 °F) and average winter temperatures ranging from −12 to −16 °C (10.4 and 3.2 °F).
http://svalbard.nordicvisitor.com/travel-guide/climate-and-daylight/
Svalbard Airport observation station. Svalbard Airport station (Svalbard) is located 28 m.a.s.l. It is the closest official weather station, 3.9 km away from Longyearbyen. The station was established in October 1964. The station measures precipitation, temperature, snow depths and wind.
https://www.yr.no/place/Norway/Svalbard/Longyearbyen/statistics.html
More importantly, it is the best time to see polar bears! It is not uncommon to have periods of fog during this time and weather in Svalbard can change very quickly. This is also the period of the Midnight Sun phenomenon, when the sun doesn't dip below the horizon, resulting in constant daylight.
https://www.naturalworldsafaris.com/polar-regions/svalbard/when-to-go
Climate of Svalbard. The climate of Svalbard is principally a result of its latitude, which is between 74° and 81° north. Average July temperatures range from 3 and 7 °C (37.4 and 44.6 °F) , and in January temperatures are normally between −13 and −20 °C (8.6 and −4.0 °F).
https://en.wikipedia.org/wiki/Climate_of_Svalbard
Average Weather in August in Longyearbyen Svalbard & Jan Mayen. In Longyearbyen, the month of August is characterized by falling daily high temperatures, with daily highs decreasing by 5°F, from 47°F to 41°F over the course of the month, and rarely exceeding 52°F or dropping below 36°F.
https://weatherspark.com/m/80119/8/Average-Weather-in-August-in-Longyearbyen-Svalbard-&amp;-Jan-Mayen
The best time to see wildlife in Svalbard is during the months of May to early September. There are also 11 species of whales in the region, which are found in the summer months, and during the winter they find it difficult to surface and take air, heading south instead.
https://www.naturalworldsafaris.com/polar-regions/svalbard/when-to-go
For more, detailed information: the Guidebook Spitsbergen-Svalbard. The average annual temperature in Isfjord is -7,5°C, which is warm considering the latitude of 78°N, a consequence of the influence of the West Spitsbergen Current (Gulf stream). The climate is accordingly high arctic with a strong maritime component.
https://www.spitsbergen-svalbard.com/spitsbergen-information/climate.html
Average Hourly Temperature in August. The average hourly temperature, color coded into bands: frigid < 15°F < freezing < 32°F < chilly < 45°F < cold < 55°F < cool < 65°F < comfortable < 75°F < warm < 85°F < hot < 95°F < sweltering. The shaded overlays indicate night and civil twilight.
https://weatherspark.com/m/80119/8/Average-Weather-in-August-in-Longyearbyen-Svalbard-&amp;-Jan-Mayen
climate and daylight. Climate and daylight in Svalbard. Svalbard has an Arctic climate tempered by the warm North Atlantic Current, with average summer temperatures ranging from 4 to 6 °C (39.2 to 42.8 °F) and average winter temperatures ranging from −12 to −16 °C (10.4 and 3.2 °F).
http://svalbard.nordicvisitor.com/travel-guide/climate-and-daylight/
temperature in svalbard in august
In Longyearbyen, the month of August is characterized by falling daily high temperatures, with daily highs decreasing by 5 degrees Fahrenheit, from 47 degrees Fahrenheit to 41 degrees Fahrenheit over the course of the month, and rarely exceeding 52°F or dropping below 36 degrees Fahrenheit.   Temperature in Svalbard in august, 5 degree Fahrenheit, from 47 degree Fahrenheit to 41 degree Fahrenheit over the course of the month, and rarely exceeding 52 degree Fahrenheit or dropping below 36 degree Fahrenheit.