Average Weather in September in La Unión Mexico
Daily high temperatures are around 89°F, rarely falling below 85°F or exceeding 93°F. The lowest daily average high temperature is 89°F on September 13.
Daily low temperatures are around 74°F, rarely falling below 71°F or exceeding 76°F.
For reference, on May 28, the hottest day of the year, temperatures in La Unión typically range from 72°F to 91°F, while on January 23, the coldest day of the year, they range from 64°F to 87°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
Thiès Nones, Senegal (5,582 miles away); Mingoyo, Tanzania (9,811 miles); and Ambilobe, Madagascar (10,483 miles) are the far-away foreign places with temperatures most similar to La Unión (view comparison).
The month of September in La Unión experiences gradually decreasing cloud cover, with the percentage of time that the sky is overcast or mostly cloudy decreasing from 91% to 87%. The highest chance of overcast or mostly cloudy conditions is 91% on September 3.
The clearest day of the month is September 30, with clear, mostly clear, or partly cloudy conditions 13% of the time.
For reference, on September 3, the cloudiest day of the year, the chance of overcast or mostly cloudy conditions is 91%, while on February 29, the clearest day of the year, the chance of clear, mostly clear, or partly cloudy skies is 70%.
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. In La Unión, the chance of a wet day over the course of September is very rapidly decreasing, starting the month at 63% and ending it at 47%.
For reference, the year's highest daily chance of a wet day is 65% on September 13, and its lowest chance is 0% on April 4.
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 La Unión is rapidly decreasing, starting the month at 7.3 inches, when it rarely exceeds 13.3 inches or falls below 3.1 inches, and ending the month at 5.4 inches, when it rarely exceeds 9.6 inches or falls below 1.9 inches.
The highest average 31-day accumulation is 7.4 inches on September 5.
Average Monthly Rainfall in September
Over the course of September in La Unión, the length of the day is gradually decreasing. From the start to the end of the month, the length of the day decreases by 29 minutes, implying an average daily decrease of 1 minute, 0 seconds, and weekly decrease of 7 minutes, 0 seconds.
The shortest day of the month is September 30, with 11 hours, 59 minutes of daylight and the longest day is September 1, with 12 hours, 28 minutes of daylight.
Hours of Daylight and Twilight in September
The earliest sunrise of the month in La Unión is 7:33 AM on September 1 and the latest sunrise is 4 minutes later at 7:37 AM on September 30.
The latest sunset is 8:00 PM on September 1 and the earliest sunset is 25 minutes earlier at 7:36 PM on September 30.
Daylight saving time is observed in La Unión during 2020, but it neither starts nor ends during September, so the entire month is in daylight saving time.
For reference, on June 20, the longest day of the year, the Sun rises at 7:12 AM and sets 13 hours, 13 minutes later, at 8:25 PM, while on December 21, the shortest day of the year, it rises at 7:14 AM and sets 11 hours, 3 minutes later, at 6:17 PM.
Sunrise & Sunset with Twilight and Daylight Saving Time 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 La Unión is essentially constant during September, remaining around 100% throughout.
For reference, on August 14, the muggiest day of the year, there are muggy conditions 100% of the time, while on March 7, the least muggy day of the year, there are muggy conditions 68% 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 in La Unión is essentially constant during September, remaining within 0.3 miles per hour of 6.0 miles per hour throughout.
For reference, on May 21, the windiest day of the year, the daily average wind speed is 7.2 miles per hour, while on November 29, the calmest day of the year, the daily average wind speed is 5.0 miles per hour.
The highest daily average wind speed during September is 6.2 miles per hour on September 12.
Average Wind Speed in September
The hourly average wind direction in La Unión throughout September is predominantly from the south, with a peak proportion of 46% on September 14.
Wind Direction in September
La Unión 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 La Unión is essentially constant during September, remaining around 85°F throughout.
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).
Temperatures in La Unión 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.
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 in La Unión are rapidly increasing during September, increasing by 868°F, from 6,851°F to 7,718°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 in La Unión is essentially constant during September, remaining within 0.1 kWh of 4.5 kWh throughout.
Average Daily Incident Shortwave Solar Energy in September
For the purposes of this report, the geographical coordinates of La Unión are 17.986 deg latitude, -101.807 deg longitude, and 364 ft elevation.
The topography within 2 miles of La Unión contains very significant variations in elevation, with a maximum elevation change of 1,260 feet and an average elevation above sea level of 341 feet. Within 10 miles contains very significant variations in elevation (3,494 feet). Within 50 miles also contains extreme variations in elevation (8,911 feet).
The area within 2 miles of La Unión is covered by cropland (56%) and trees (43%), within 10 miles by trees (45%) and cropland (39%), and within 50 miles by trees (39%) and water (35%).
This report illustrates the typical weather in La Unión 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 is only a single weather station, Ixtapa-Zihuatanejo International Airport, in our network suitable to be used as a proxy for the historical temperature and dew point records of La Unión.
At a distance of 56 kilometers from La Unión, 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 La Unión 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.
All 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 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.