Average Weather in September at Seward Airport Alaska, United States
Daily high temperatures decrease by 9°F, from 59°F to 50°F, rarely falling below 46°F or exceeding 66°F.
Daily low temperatures decrease by 7°F, from 47°F to 40°F, rarely falling below 33°F or exceeding 51°F.
For reference, on July 30, the hottest day of the year, temperatures at Seward Airport typically range from 51°F to 62°F, while on January 20, the coldest day of the year, they range from 22°F to 31°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
frigid 15°F freezing 32°F very cold 45°F cold 55°F cool 65°F comfortable 75°F warm 85°F hot 95°F sweltering
The month of September at Seward Airport experiences essentially constant cloud cover, with the percentage of time that the sky is overcast or mostly cloudy remaining about 68% throughout the month. The highest chance of overcast or mostly cloudy conditions is 69% on September 19.
The clearest day of the month is September 1, with clear, mostly clear, or partly cloudy conditions 33% of the time.
For reference, on December 19, the cloudiest day of the year, the chance of overcast or mostly cloudy conditions is 72%, while on March 16, the clearest day of the year, the chance of clear, mostly clear, or partly cloudy skies is 38%.
Cloud Cover Categories in September
0% clear 20% mostly clear 40% partly cloudy 60% mostly cloudy 80% overcast 100%
A wet day is one with at least 0.04 inches of liquid or liquid-equivalent precipitation. At Seward Airport, the chance of a wet day over the course of September is rapidly increasing, starting the month at 50% and ending it at 57%.
For reference, the year's highest daily chance of a wet day is 57% on September 24, and its lowest chance is 38% on June 24.
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 at Seward Airport is rapidly increasing, starting the month at 8.3 inches, when it rarely exceeds 13.8 inches or falls below 3.7 inches, and ending the month at 9.8 inches, when it rarely exceeds 14.7 inches or falls below 5.1 inches.
The highest average 31-day accumulation is 9.9 inches on September 23.
Average Monthly Rainfall in September
Over the course of September at Seward Airport, 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, 37 minutes, implying an average daily decrease of 5 minutes, 25 seconds, and weekly decrease of 37 minutes, 54 seconds.
The shortest day of the month is September 30, with 11 hours, 32 minutes of daylight and the longest day is September 1, with 14 hours, 9 minutes of daylight.
Hours of Daylight and Twilight in September
The earliest sunrise of the month at Seward Airport is 6:52 AM on September 1 and the latest sunrise is 1 hour, 9 minutes later at 8:00 AM on September 30.
The latest sunset is 9:01 PM on September 1 and the earliest sunset is 1 hour, 28 minutes earlier at 7:32 PM on September 30.
Daylight saving time is observed at Seward Airport during 2019, but it neither starts nor ends during September, so the entire month is in daylight saving time.
For reference, on June 21, the longest day of the year, the Sun rises at 4:31 AM and sets 18 hours, 55 minutes later, at 11:27 PM, while on December 22, the shortest day of the year, it rises at 10:01 AM and sets 5 hours, 50 minutes later, at 3:51 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 at Seward Airport is essentially constant during September, remaining around 0% throughout.
For reference, on July 29, the muggiest day of the year, there are muggy conditions 0% of the time, while on January 1, the least muggy day of the year, there are muggy conditions 0% of the time.
Humidity Comfort Levels in September
dry 55°F comfortable 60°F humid 65°F muggy 70°F oppressive 75°F miserable
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 at Seward Airport is increasing during September, increasing from 7.1 miles per hour to 8.7 miles per hour over the course of the month.
For reference, on January 8, the windiest day of the year, the daily average wind speed is 10.8 miles per hour, while on July 6, the calmest day of the year, the daily average wind speed is 5.5 miles per hour.
Average Wind Speed in September
Wind Direction in September
Seward Airport 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 at Seward Airport is decreasing during September, falling by 4°F, from 54°F to 51°F, over the course of the month.
Average Water Temperature in September
Definitions 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 at Seward Airport typically lasts for 5.0 months (153 days), from around May 6 to around October 6, rarely starting before April 14 or after May 25, and rarely ending before September 17 or after October 24.
The month of September at Seward Airport is more likely than not fully within the growing season, with the chance that a given day is in the growing season rapidly decreasing from 99% to 67% over the course of the month.
Time Spent in Various Temperature Bands and the Growing Season in September
frigid 15°F freezing 32°F very cold 45°F cold 55°F cool 65°F comfortable 75°F warm 85°F hot 95°F sweltering
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 at Seward Airport are gradually increasing during September, increasing by 47°F, from 441°F to 489°F, over the course of the month.
Growing Degree Days 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 at Seward Airport is decreasing during September, falling by 1.3 kWh, from 3.1 kWh to 1.8 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 Seward Airport are 60.134 deg latitude, -149.423 deg longitude, and 210 ft elevation.
The topography within 2 miles of Seward Airport contains large variations in elevation, with a maximum elevation change of 2,858 feet and an average elevation above sea level of 266 feet. Within 10 miles contains large variations in elevation (5,614 feet). Within 50 miles also contains extreme variations in elevation (6,598 feet).
The area within 2 miles of Seward Airport is covered by trees (42%), water (29%), and shrubs (11%), within 10 miles by trees (23%) and snow and glaciers (21%), and within 50 miles by water (32%) and snow and glaciers (21%).
This report illustrates the typical weather at Seward Airport 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
Seward Airport 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.
In the case of missing or erroneous measurements from this station, we fall back on records from nearby stations, adjusted according to typical seasonal and diurnal intra-station differences. For a given day of the year and hour of the day, the fallback station is selected to minimize the prediction error over the years for which there are measurements for both stations.
The stations on which we may fall back include but are not limited to Portage, Portage Glacier; Whittier Airport; Bryant Army Heliport; Merrill Field Airport; Lake Hood Seaplane Base; Elmendorf Air Force Base; Anchorage International Airport; and Birchwood Airport.
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.
The 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.