September Weather in Unalaska United StatesDaily high temperatures decrease by 6°F, from 55°F to 49°F, rarely falling below 45°F or exceeding 61°F. Daily low temperatures decrease by 5°F, from 48°F to 43°F, rarely falling below 39°F or exceeding 52°F. For reference, on August 13, the hottest day of the year, temperatures in Unalaska typically range from 49°F to 56°F, while on January 23, the coldest day of the year, they range from 30°F to 36°F. 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. Ólafsvík, Iceland (4,002 miles away) and Evjen, Norway (4,002 miles) are the far-away foreign places with temperatures most similar to Unalaska (view comparison). CloudsThe month of September in Unalaska experiences decreasing cloud cover, with the percentage of time that the sky is overcast or mostly cloudy decreasing from 70% to 61%. The clearest day of the month is September 29, with clear, mostly clear, or partly cloudy conditions 39% of the time. For reference, on July 16, the cloudiest day of the year, the chance of overcast or mostly cloudy conditions is 82%, while on October 13, the clearest day of the year, the chance of clear, mostly clear, or partly cloudy skies is 41%. PrecipitationA wet day is one with at least 0.04 inches of liquid or liquid-equivalent precipitation. In Unalaska, the chance of a wet day over the course of September is gradually increasing, starting the month at 37% and ending it at 40%. For reference, the year's highest daily chance of a wet day is 47% on December 16, and its lowest chance is 25% on May 4. RainfallTo 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 Unalaska is increasing, starting the month at 3.1 inches, when it rarely exceeds 4.7 inches or falls below 1.5 inches, and ending the month at 3.7 inches, when it rarely exceeds 5.9 inches or falls below 1.8 inches. SunOver the course of September in Unalaska, 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 2 hours, 3 minutes, implying an average daily decrease of 4 minutes, 15 seconds, and weekly decrease of 29 minutes, 42 seconds. The shortest day of the month is September 30, with 11 hours, 35 minutes of daylight and the longest day is September 1, with 13 hours, 38 minutes of daylight. The earliest sunrise of the month in Unalaska is 7:16 AM on September 1 and the latest sunrise is 52 minutes later at 8:07 AM on September 30. The latest sunset is 8:54 PM on September 1 and the earliest sunset is 1 hour, 11 minutes earlier at 7:42 PM on September 30. Daylight saving time is observed in Unalaska during 2024, but it neither starts nor ends during September, so the entire month is in standard time. For reference, on June 20, the longest day of the year, the Sun rises at 5:34 AM and sets 17 hours, 7 minutes later, at 10:41 PM, while on December 21, the shortest day of the year, it rises at 9:22 AM and sets 7 hours, 24 minutes later, at 4:46 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 September 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 Unalaska is essentially constant during September, 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 Unalaska is rapidly increasing during September, increasing from 14.1 miles per hour to 17.7 miles per hour over the course of the month. For reference, on November 24, the windiest day of the year, the daily average wind speed is 20.2 miles per hour, while on July 17, the calmest day of the year, the daily average wind speed is 11.2 miles per hour. The hourly average wind direction in Unalaska throughout September is predominantly from the west, with a peak proportion of 44% on September 2. Water TemperatureUnalaska 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 Unalaska is gradually decreasing during September, falling by 2°F, from 49°F to 47°F, over the course of the month. 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 Unalaska typically lasts for 6.4 months (195 days), from around April 28 to around November 9, rarely starting before April 7 or after May 19, and rarely ending before October 15 or after December 8. The month of September in Unalaska 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 Unalaska are essentially constant during September, remaining within 14°F of 142°F throughout. 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 Unalaska is gradually decreasing during September, falling by 1.0 kWh, from 3.2 kWh to 2.2 kWh, over the course of the month. TopographyFor the purposes of this report, the geographical coordinates of Unalaska are 53.874 deg latitude, -166.537 deg longitude, and 26 ft elevation. The topography within 2 miles of Unalaska contains very significant variations in elevation, with a maximum elevation change of 1,850 feet and an average elevation above sea level of 255 feet. Within 10 miles contains very significant variations in elevation (3,547 feet). Within 50 miles also contains extreme variations in elevation (5,971 feet). The area within 2 miles of Unalaska is covered by water (55%), grassland (19%), and shrubs (14%), within 10 miles by water (41%) and shrubs (24%), and within 50 miles by water (86%). Data SourcesThis report illustrates the typical weather in Unalaska, 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, Unalaska Airport, in our network suitable to be used as a proxy for the historical temperature and dew point records of Unalaska. At a distance of 2 kilometers from Unalaska, 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 Unalaska 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. |