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Average Weather in September in San Juan Bautista California, United States

In San Juan Bautista, the month of September is characterized by essentially constant daily high temperatures, with daily highs around 78°F throughout the month, rarely exceeding 88°F or dropping below 69°F. The highest daily average high temperature is 78°F on September 11.

Daily low temperatures decrease by 2°F, from 54°F to 52°F, rarely falling below 46°F or exceeding 58°F.

For reference, on September 10, the hottest day of the year, temperatures in San Juan Bautista typically range from 54°F to 78°F, while on January 3, the coldest day of the year, they range from 39°F to 60°F.

Average High and Low Temperature in September

The daily average high (red line) and low (blue line) temperature, with 25th to 75th and 10th to 90th percentile bands. The thin dotted lines are the corresponding average perceived temperatures.

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

Average Hourly Temperature in September in San Juan Bautista12 AM4 AM8 AM12 PM4 PM8 PM12 AM18152229112233445566778899101011111212131314141515161617171818191920202121222223232424252526262727282829293030AugOctcoldcoolcomfortablewarm
The average hourly temperature, color coded into bands: frigid < 15°F < freezing < 32°F < chilly < 45°F < cold < 55°F < cool < 65°F < comfortable < 75°F < warm < 85°F < hot < 95°F < sweltering. The shaded overlays indicate night and civil twilight.

Clouds

The month of September in San Juan Bautista experiences gradually increasing cloud cover, with the percentage of time that the sky is overcast or mostly cloudy increasing from 9% to 16%.

The clearest day of the month is September 1, with clear, mostly clear, or partly cloudy conditions 91% of the time.

For reference, on February 16, the cloudiest day of the year, the chance of overcast or mostly cloudy conditions is 53%, while on July 29, the clearest day of the year, the chance of clear, mostly clear, or partly cloudy skies is 92%.

Cloud Cover in September

The percentage of time spent in each cloud cover band, categorized by the percentage of the sky covered by clouds: clear < 20% < mostly clear < 40% < partly cloudy < 60% < mostly cloudy < 80% < overcast.

Precipitation

A wet day is one with at least 0.04 inches of liquid or liquid-equivalent precipitation. In San Juan Bautista, the chance of a wet day over the course of September is gradually increasing, starting the month at 1% and ending it at 4%.

For reference, the year's highest daily chance of a wet day is 30% on February 21, and its lowest chance is 0% on July 22.

Probability of Precipitation in September

The percentage of days in which various types of precipitation are observed, excluding trace quantities: rain alone, snow alone, and mixed (both rain and snow fell in the same day).

Rainfall

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 San Juan Bautista is gradually increasing, starting the month at 0.1 inches, when it rarely exceeds 0.2 inches or falls below -0.0 inches, and ending the month at 0.4 inches, when it rarely exceeds 1.2 inches or falls below -0.0 inches.

Average Monthly Rainfall in September

The average rainfall (solid line) accumulated over the course of a sliding 31-day period centered on the day in question, with 25th to 75th and 10th to 90th percentile bands. The thin dotted line is the corresponding average liquid-equivalent snowfall.

Sun

Over the course of September in San Juan Bautista, the length of the day is rapidly decreasing. From the start to the end of the month, the length of the day decreases by 1 hour, 7 minutes, implying an average daily decrease of 2 minutes, 19 seconds, and weekly decrease of 16 minutes, 11 seconds.

The shortest day of the month is September 30, with 11 hours, 49 minutes of daylight and the longest day is September 1, with 12 hours, 57 minutes of daylight.

Hours of Daylight and Twilight in September

The number of hours during which the Sun is visible (black line). From bottom (most yellow) to top (most gray), the color bands indicate: full daylight, twilight (civil, nautical, and astronomical), and full night.

The earliest sunrise of the month in San Juan Bautista is 6:37 AM on September 1 and the latest sunrise is 24 minutes later at 7:00 AM on September 30.

The latest sunset is 7:33 PM on September 1 and the earliest sunset is 44 minutes earlier at 6:50 PM on September 30.

Daylight saving time is observed in San Juan Bautista during 2017, 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 5:47 AM and sets 14 hours, 41 minutes later, at 8:28 PM, while on December 21, the shortest day of the year, it rises at 7:15 AM and sets 9 hours, 38 minutes later, at 4:53 PM.

Sunrise & Sunset with Twilight in September

The solar day over the course of September. From bottom to top, the black lines are the previous solar midnight, sunrise, solar noon, sunset, and the next solar midnight. The day, twilights (civil, nautical, and astronomical), and night are indicated by the color bands from yellow to gray.

Humidity

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 San Juan Bautista is essentially constant during September, remaining around 0% throughout.

For reference, on September 9, 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

Humidity Comfort Levels in September in San Juan Bautista0%10%20%30%40%50%60%70%80%90%100%18152229112233445566778899101011111212131314141515161617171818191920202121222223232424252526262727282829293030AugOctSep 110%Sep 110%Sep 10%Sep 10%Sep 300%Sep 300%Sep 210%Sep 210%comfortablecomfortabledrydryhumidhumid
The percentage of time spent at various humidity comfort levels, categorized by dew point: dry < 55°F < comfortable < 60°F < humid < 65°F < muggy < 70°F < oppressive < 75°F < miserable.

Wind

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 San Juan Bautista is essentially constant during September, remaining within 0.1 miles per hour of 3.4 miles per hour throughout.

For reference, on June 5, the windiest day of the year, the daily average wind speed is 4.4 miles per hour, while on October 21, the calmest day of the year, the daily average wind speed is 3.1 miles per hour.

Average Wind Speed in September

The average of mean hourly wind speeds (dark gray line), with 25th to 75th and 10th to 90th percentile bands.
The hourly average wind direction in San Juan Bautista throughout September is predominantly from the west, with a peak proportion of 86% on September 1.

Wind Direction in September

Wind Direction in September in San Juan Bautista0%20%40%60%80%100%18152229112233445566778899101011111212131314141515161617171818191920202121222223232424252526262727282829293030AugOctwestsouthnorth
The percentage of hours in which the mean wind direction is from each of the four cardinal wind directions (north, east, south, and west), excluding hours in which the mean wind speed is less than 1 mph. The lightly tinted areas at the boundaries are the percentage of hours spent in the implied intermediate directions (northeast, southeast, southwest, and northwest).

Water Temperature

San Juan Bautista 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 Juan Bautista is essentially constant during September, remaining around 58°F throughout.

The highest average surface water temperature during September is 59°F on September 23.

Average Water Temperature in September

The daily average water temperature (purple line), with 25th to 75th and 10th to 90th percentile bands.

Solar Energy

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 San Juan Bautista is decreasing during September, falling by 1.5 kWh, from 7.0 kWh to 5.5 kWh, over the course of the month.

Average Daily Incident Shortwave Solar Energy in September

The average daily shortwave solar energy reaching the ground per square meter (orange line), with 25th to 75th and 10th to 90th percentile bands.

Topography

For the purposes of this report, the geographical coordinates of San Juan Bautista are 36.846 deg latitude, -121.538 deg longitude, and 322 ft elevation.

The topography within 2 miles of San Juan Bautista contains very significant variations in elevation, with a maximum elevation change of 981 feet and an average elevation above sea level of 323 feet. Within 10 miles contains very significant variations in elevation (3,051 feet). Within 50 miles contains large variations in elevation (5,850 feet).

The area within 2 miles of San Juan Bautista is covered by cropland (45%) and grassland (44%), within 10 miles by grassland (45%) and cropland (23%), and within 50 miles by grassland (30%) and shrubs (20%).

Data Sources

This report illustrates the typical weather in San Juan Bautista 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 3 weather stations near enough to contribute to our estimation of the temperature and dew point in San Juan Bautista.

For each station, the records are corrected for the elevation difference between that station and San Juan Bautista 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 Juan Bautista is computed as the weighted average of the individual contributions from each station, with weights proportional to the inverse of the distance between San Juan Bautista and a given station.

The stations contributing to this reconstruction are: Hollister Municipal Airport (56%, 12 kilometers, northeast); Salinas Municipal Airport (24%, 21 kilometers, south); and Watsonville Municipal Airport (20%, 25 kilometers, northwest).

Other Data

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.