Average Weather in September in San Marcos California, United States
Daily high temperatures decrease by 3°F, from 80°F to 77°F, rarely falling below 70°F or exceeding 88°F.
Daily low temperatures decrease by 4°F, from 64°F to 61°F, rarely falling below 55°F or exceeding 69°F.
For reference, on August 24, the hottest day of the year, temperatures in San Marcos typically range from 65°F to 81°F, while on December 27, the coldest day of the year, they range from 45°F to 64°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
Rabat, Morocco (5,969 miles away); Cape Town, South Africa (9,910 miles); and Kruisfontein, South Africa (10,267 miles) are the far-away foreign places with temperatures most similar to San Marcos (view comparison).
The month of September in San Marcos experiences essentially constant cloud cover, with the percentage of time that the sky is overcast or mostly cloudy remaining about 11% throughout the month. The lowest chance of overcast or mostly cloudy conditions is 10% on September 7.
The clearest day of the month is September 7, with clear, mostly clear, or partly cloudy conditions 90% of the time.
For reference, on February 20, the cloudiest day of the year, the chance of overcast or mostly cloudy conditions is 43%, while on September 7, the clearest day of the year, the chance of clear, mostly clear, or partly cloudy skies is 90%.
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 San Marcos, the chance of a wet day over the course of September is essentially constant, remaining around 4% throughout.
For reference, the year's highest daily chance of a wet day is 21% on February 22, and its lowest chance is 1% on June 26.
Probability of Precipitation in September
The average sliding 31-day rainfall during September in San Marcos is essentially constant, remaining about 0.2 inches throughout, and rarely exceeding 1.2 inches or falling below -0.0 inches.
Average Monthly Rainfall in September
Over the course of September in San Marcos, the length of the day is decreasing. From the start to the end of the month, the length of the day decreases by 58 minutes, implying an average daily decrease of 2 minutes, 1 second, and weekly decrease of 14 minutes, 6 seconds.
The shortest day of the month is September 30, with 11 hours, 52 minutes of daylight and the longest day is September 1, with 12 hours, 50 minutes of daylight.
Hours of Daylight and Twilight in September
The earliest sunrise of the month in San Marcos is 6:23 AM on September 1 and the latest sunrise is 19 minutes later at 6:42 AM on September 30.
The latest sunset is 7:13 PM on September 1 and the earliest sunset is 39 minutes earlier at 6:34 PM on September 30.
Daylight saving time is observed in San Marcos during 2018, 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 5:40 AM and sets 14 hours, 21 minutes later, at 8:00 PM, while on December 21, the shortest day of the year, it rises at 6:48 AM and sets 9 hours, 58 minutes later, at 4:45 PM.
Sunrise & Sunset with Twilight in September
The chance that a given day will be muggy in San Marcos is gradually decreasing during September, falling from 7% to 3% over the course of the month.
For reference, on August 27, the muggiest day of the year, there are muggy conditions 7% of the time, while on November 3, 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
The average hourly wind speed in San Marcos is essentially constant during September, remaining within 0.1 miles per hour of 5.5 miles per hour throughout.
For reference, on April 11, the windiest day of the year, the daily average wind speed is 7.4 miles per hour, while on September 8, the calmest day of the year, the daily average wind speed is 5.4 miles per hour.
The lowest daily average wind speed during September is 5.4 miles per hour on September 9.
Average Wind Speed in September
Wind Direction in September
San Marcos 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 San Marcos is essentially constant during September, remaining within 1°F of 69°F throughout.
Average Water Temperature in September
Temperatures in San Marcos 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
The average accumulated growing degree days in San Marcos are rapidly increasing during September, increasing by 571°F, from 3,015°F to 3,586°F, over the course of the month.
Growing Degree Days in September
The average daily incident shortwave solar energy in San Marcos is decreasing during September, falling by 1.1 kWh, from 7.0 kWh to 5.8 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 San Marcos are 33.143 deg latitude, -117.166 deg longitude, and 705 ft elevation.
The topography within 2 miles of San Marcos contains significant variations in elevation, with a maximum elevation change of 778 feet and an average elevation above sea level of 685 feet. Within 10 miles contains significant variations in elevation (2,077 feet). Within 50 miles contains large variations in elevation (8,258 feet).
The area within 2 miles of San Marcos is covered by artificial surfaces (71%) and shrubs (28%), within 10 miles by artificial surfaces (43%) and shrubs (39%), and within 50 miles by shrubs (44%) and water (33%).
This report illustrates the typical weather in San Marcos 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 4 weather stations near enough to contribute to our estimation of the temperature and dew point in San Marcos.
For each station, the records are corrected for the elevation difference between that station and San Marcos 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 San Marcos is computed as the weighted average of the individual contributions from each station, with weights proportional to the inverse of the distance between San Marcos and a given station.
The stations contributing to this reconstruction are: McClellan–Palomar Airport (58%, 11 kilometers, west); Ramona Airport (19%, 26 kilometers, southeast); Miramar Marine Corps Air Station (20%, 31 kilometers, south); and Palm Springs International Airport (3.7%, 97 kilometers, northeast).
Time zones for aiports and weather stations are provided by AskGeo.com .