Average Weather in September in Reykjavík Iceland
In Reykjavík, the month of September is characterized by falling daily high temperatures, with daily highs decreasing by 6°F, from 54°F to 48°F over the course of the month, and rarely exceeding 58°F or dropping below 41°F.
Daily low temperatures decrease by 6°F, from 45°F to 40°F, rarely falling below 32°F or exceeding 51°F.
For reference, on July 31, the hottest day of the year, temperatures in Reykjavík typically range from 49°F to 57°F, while on January 24, the coldest day of the year, they range from 28°F to 36°F.
Average High and Low Temperature in September
The figure below shows you a compact characterization of the hourly average temperatures for the quarter of the year centered on September. 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.
Average Hourly Temperature in September
The month of September in Reykjavík experiences essentially constant cloud cover, with the percentage of time that the sky is overcast or mostly cloudy remaining about 65% throughout the month.
The clearest day of the month is September 27, with clear, mostly clear, or partly cloudy conditions 36% of the time.
For reference, on January 21, the cloudiest day of the year, the chance of overcast or mostly cloudy conditions is 78%, while on May 21, the clearest day of the year, the chance of clear, mostly clear, or partly cloudy skies is 43%.
Cloud Cover Categories in September
A wet day is one with at least 0.04 inches of liquid or liquid-equivalent precipitation. In Reykjavík, the chance of a wet day over the course of September is gradually increasing, starting the month at 44% and ending it at 46%.
For reference, the year's highest daily chance of a wet day is 55% on February 26, and its lowest chance is 29% on July 7.
Probability of Precipitation in September
To show variation within the month and not just the monthly total, we show the rainfall accumulated over a sliding 31-day period centered around each day.
The average sliding 31-day rainfall during September in Reykjavík is increasing, starting the month at 4.1 inches, when it rarely exceeds 6.3 inches or falls below 2.0 inches, and ending the month at 4.6 inches, when it rarely exceeds 7.1 inches or falls below 2.4 inches.
The highest average 31-day accumulation is 4.6 inches on September 28.
Average Monthly Rainfall in September
Over the course of September in Reykjavík, the length of the day is very rapidly decreasing. From the start to the end of the month, the length of the day decreases by 3 hours, 7 minutes, implying an average daily decrease of 6 minutes, 26 seconds, and weekly decrease of 45 minutes, 5 seconds.
The shortest day of the month is September 30, with 11 hours, 25 minutes of daylight and the longest day is September 1, with 14 hours, 32 minutes of daylight.
Hours of Daylight and Twilight in September
The earliest sunrise of the month in Reykjavík is 6:10 AM on September 1 and the latest sunrise is 1 hour, 24 minutes later at 7:33 AM on September 30.
The latest sunset is 8:42 PM on September 1 and the earliest sunset is 1 hour, 43 minutes earlier at 6:59 PM on September 30.
Daylight saving time is not observed in Reykjavík during 2017.
For reference, on June 21, the longest day of the year, the Sun rises at 2:55 AM and sets 21 hours, 9 minutes later, at 12:03 AM, while on December 21, the shortest day of the year, it rises at 11:22 AM and sets 4 hours, 7 minutes later, at 3:29 PM.
Sunrise & Sunset with Twilight in September
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.
The chance that a given day will be muggy in Reykjavík is essentially constant during September, remaining around 0% throughout.
Humidity Comfort Levels in September
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 Reykjavík is gradually increasing during September, increasing from 5.2 miles per hour to 6.1 miles per hour over the course of the month.
For reference, on January 7, the windiest day of the year, the daily average wind speed is 8.7 miles per hour, while on July 21, the calmest day of the year, the daily average wind speed is 4.3 miles per hour.
Average Wind Speed in September
Wind Direction in September
Reykjavík 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 surface water temperature in Reykjavík is gradually decreasing during September, falling by 3°F, from 51°F to 48°F, over the course of the month.
Average Water Temperature in September
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 in Reykjavík is decreasing during September, falling by 1.4 kWh, from 2.9 kWh to 1.5 kWh, over the course of the month.
Average Daily Incident Shortwave Solar Energy in September
For the purposes of this report, the geographical coordinates of Reykjavík are 64.135 deg latitude, -21.895 deg longitude, and 3 ft elevation.
The topography within 2 miles of Reykjavík contains only modest variations in elevation, with a maximum elevation change of 203 feet and an average elevation above sea level of 57 feet. Within 10 miles contains only modest variations in elevation (2,851 feet). Within 50 miles contains large variations in elevation (4,426 feet).
The area within 2 miles of Reykjavík is covered by artificial surfaces (83%), within 10 miles by water (39%) and shrubs (30%), and within 50 miles by water (53%) and shrubs (23%).
This report illustrates the typical weather in Reykjavík year round, 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 Reykjavík.
For each station, the records are corrected for the elevation difference between that station and Reykjavík 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 Reykjavík is computed as the weighted average of the individual contributions from each station, with weights proportional to the inverse of the distance between Reykjavík and a given station.
All data relating to the Sun's position (e.g., sunrise and sunset) are computed using astronomical formulas from the book, Astronomical Tables of the Sun, Moon and Planets , 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 aiports and weather stations are provided by AskGeo.com .
Maps are © Esri, with data from National Geographic, Esri, DeLorme, NAVTEQ, UNEP-WCMC, USGS, NASA, ESA, METI, NRCAN, GEBCO, NOAA, and iPC.