September Weather in São Luís Brazil
Daily high temperatures are around 90°F, rarely falling below 87°F or exceeding 92°F.
Daily low temperatures are around 78°F, rarely falling below 76°F or exceeding 80°F.
For reference, on October 22, the hottest day of the year, temperatures in São Luís typically range from 79°F to 90°F, while on April 4, the coldest day of the year, they range from 77°F to 87°F.
Average High and Low Temperature in September in São Luís
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 in São Luís
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 in São Luís experiences increasing cloud cover, with the percentage of time that the sky is overcast or mostly cloudy increasing from 35% to 46%.
The clearest day of the month is September 2, with clear, mostly clear, or partly cloudy conditions 65% of the time.
For reference, on April 13, the cloudiest day of the year, the chance of overcast or mostly cloudy conditions is 85%, while on August 11, the clearest day of the year, the chance of clear, mostly clear, or partly cloudy skies is 68%.
Cloud Cover Categories in September in São Luís
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 São Luís, the chance of a wet day over the course of September is essentially constant, remaining around 6% throughout.
For reference, the year's highest daily chance of a wet day is 86% on April 7, and its lowest chance is 4% on October 31.
Probability of Precipitation in September in São Luís
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 São Luís is essentially constant, remaining about 0.5 inches throughout, and rarely exceeding 1.0 inches.
Average Monthly Rainfall in September in São Luís
Over the course of September in São Luís, the length of the day is essentially constant. The shortest day of the month is September 1, with 12 hours, 4 minutes of daylight and the longest day is September 30, with 12 hours, 8 minutes of daylight.
Hours of Daylight and Twilight in September in São Luís
The latest sunrise of the month in São Luís is 5:55 AM on September 1 and the earliest sunrise is 12 minutes earlier at 5:43 AM on September 30.
The latest sunset is 5:58 PM on September 1 and the earliest sunset is 8 minutes earlier at 5:50 PM on September 30.
Daylight saving time is not observed in São Luís during 2021.
For reference, on December 21, the longest day of the year, the Sun rises at 5:47 AM and sets 12 hours, 16 minutes later, at 6:03 PM, while on June 21, the shortest day of the year, it rises at 5:59 AM and sets 11 hours, 59 minutes later, at 5:58 PM.
Sunrise & Sunset with Twilight in September in São Luís
The figure below presents a compact representation of key lunar data for September 2021. The horizontal axis is the day, the vertical axis is the hour of the day, and the colored areas indicate when the moon is above the horizon. The vertical gray bars (new Moons) and blue bars (full Moons) indicate key Moon phases. The label associated with each bar indicates the date and time that the phase is obtained, and the companion time labels indicate the rise and set times of the Moon for the nearest time interval in which the moon is above the horizon.
Moon Rise, Set & Phases in September in São Luís
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 São Luís is essentially constant during September, remaining around 99% throughout.
For reference, on February 21, the muggiest day of the year, there are muggy conditions 100% of the time, while on August 28, the least muggy day of the year, there are muggy conditions 99% of the time.
Humidity Comfort Levels in September in São Luís
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 São Luís is gradually increasing during September, increasing from 6.3 miles per hour to 7.0 miles per hour over the course of the month.
For reference, on October 25, the windiest day of the year, the daily average wind speed is 7.2 miles per hour, while on May 4, the calmest day of the year, the daily average wind speed is 4.3 miles per hour.
Average Wind Speed in September in São Luís
The hourly average wind direction in São Luís throughout September is predominantly from the east, with a peak proportion of 75% on September 1.
Wind Direction in September in São Luís
São Luís 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 São Luís is essentially constant during September, remaining around 81°F throughout.
Average Water Temperature in September in São Luís
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 São Luís 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 in São Luís
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 São Luís are very rapidly increasing during September, increasing by 925°F, from 1,940°F to 2,866°F, over the course of the month.
Growing Degree Days in September in São Luís
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 São Luís is essentially constant during September, remaining within 0.1 kWh of 6.6 kWh throughout.
Average Daily Incident Shortwave Solar Energy in September in São Luís
For the purposes of this report, the geographical coordinates of São Luís are -2.530 deg latitude, -44.303 deg longitude, and 95 ft elevation.
The topography within 2 miles of São Luís contains only modest variations in elevation, with a maximum elevation change of 151 feet and an average elevation above sea level of 25 feet. Within 10 miles also contains only modest variations in elevation (243 feet). Within 50 miles also contains only modest variations in elevation (440 feet).
The area within 2 miles of São Luís is covered by artificial surfaces (45%), water (35%), and shrubs (11%), within 10 miles by water (69%), and within 50 miles by water (51%) and trees (17%).
This report illustrates the typical weather in São Luís, 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, Marechal Cunha Machado International Airport, in our network suitable to be used as a proxy for the historical temperature and dew point records of São Luís.
At a distance of 10 kilometers from São Luís, 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 São Luís 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 airports 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.