Average Weather in September in La Mesa California, United States
Daily high temperatures decrease by 3°F, from 83°F to 79°F, rarely falling below 71°F or exceeding 91°F.
Daily low temperatures decrease by 4°F, from 65°F to 60°F, rarely falling below 55°F or exceeding 69°F.
For reference, on August 24, the hottest day of the year, temperatures in La Mesa typically range from 65°F to 83°F, while on December 27, the coldest day of the year, they range from 44°F to 66°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 La Mesa 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 9% on September 10.
The clearest day of the month is September 10, with clear, mostly clear, or partly cloudy conditions 91% of the time.
For reference, on February 20, the cloudiest day of the year, the chance of overcast or mostly cloudy conditions is 44%, while on September 10, the clearest day of the year, the chance of clear, mostly clear, or partly cloudy skies is 91%.
Cloud Cover Categories in September
A wet day is one with at least 0.04 inches of liquid or liquid-equivalent precipitation. In La Mesa, the chance of a wet day over the course of September is essentially constant, remaining around 3% throughout.
For reference, the year's highest daily chance of a wet day is 21% on February 22, and its lowest chance is 0% on June 27.
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 Mesa is essentially constant, remaining about 0.2 inches throughout, and rarely exceeding 0.9 inches.
Average Monthly Rainfall in September
Over the course of September in La Mesa, 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 1 minute, 59 seconds, and weekly decrease of 13 minutes, 54 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 La Mesa is 6:22 AM on September 1 and the latest sunrise is 19 minutes later at 6:41 AM on September 30.
The latest sunset is 7:12 PM on September 1 and the earliest sunset is 39 minutes earlier at 6:33 PM on September 30.
Daylight saving time is observed in La Mesa 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, 19 minutes later, at 7:59 PM, while on December 21, the shortest day of the year, it rises at 6:46 AM and sets 9 hours, 60 minutes later, at 4:46 PM.
Sunrise & Sunset with Twilight in September
The chance that a given day will be muggy in La Mesa is decreasing during September, falling from 8% to 3% over the course of the month.
For reference, on August 24, the muggiest day of the year, there are muggy conditions 9% of the time, while on December 4, the least muggy day of the year, there are muggy conditions 0% of the time.
Humidity Comfort Levels in September
The average hourly wind speed in La Mesa is essentially constant during September, remaining within 0.1 miles per hour of 5.9 miles per hour throughout.
For reference, on December 30, the windiest day of the year, the daily average wind speed is 8.1 miles per hour, while on September 9, the calmest day of the year, the daily average wind speed is 5.8 miles per hour.
The lowest daily average wind speed during September is 5.8 miles per hour on September 9.
Average Wind Speed in September
Wind Direction in September
La Mesa 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 Mesa is essentially constant during September, remaining within 1°F of 69°F throughout.
Average Water Temperature in September
Temperatures in La Mesa 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 La Mesa are rapidly increasing during September, increasing by 594°F, from 3,154°F to 3,748°F, over the course of the month.
Growing Degree Days in September
The average daily incident shortwave solar energy in La Mesa is decreasing during September, falling by 1.1 kWh, from 7.0 kWh to 5.9 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 La Mesa are 32.768 deg latitude, -117.023 deg longitude, and 535 ft elevation.
The topography within 2 miles of La Mesa contains significant variations in elevation, with a maximum elevation change of 650 feet and an average elevation above sea level of 545 feet. Within 10 miles contains significant variations in elevation (2,539 feet). Within 50 miles contains large variations in elevation (6,516 feet).
The area within 2 miles of La Mesa is covered by artificial surfaces (96%), within 10 miles by artificial surfaces (62%) and shrubs (24%), and within 50 miles by shrubs (42%) and water (37%).
This report illustrates the typical weather in La Mesa 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 5 weather stations near enough to contribute to our estimation of the temperature and dew point in La Mesa.
For each station, the records are corrected for the elevation difference between that station and La Mesa 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 La Mesa is computed as the weighted average of the individual contributions from each station, with weights proportional to the inverse of the distance between La Mesa and a given station.
The stations contributing to this reconstruction are: Gillespie Field (43%, 8 kilometers, northeast); Montgomery Field Airport (27%, 12 kilometers, northwest); San Diego International Airport (11%, 15 kilometers, west); Brown Field Municipal Airport (11%, 22 kilometers, south); and Ream Field (8%, 24 kilometers, south).
Time zones for aiports and weather stations are provided by AskGeo.com .