Average Weather in September in Porto Portugal
In Porto, the month of September is characterized by gradually falling daily high temperatures, with daily highs decreasing by 4°F, from 75°F to 72°F over the course of the month, and rarely exceeding 84°F or dropping below 65°F.
Daily low temperatures decrease by 3°F, from 59°F to 56°F, rarely falling below 50°F or exceeding 64°F.
For reference, on July 29, the hottest day of the year, temperatures in Porto typically range from 60°F to 77°F, while on January 24, the coldest day of the year, they range from 44°F to 57°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 Porto experiences increasing cloud cover, with the percentage of time that the sky is overcast or mostly cloudy increasing from 30% to 41%.
The clearest day of the month is September 1, with clear, mostly clear, or partly cloudy conditions 70% of the time.
For reference, on December 16, the cloudiest day of the year, the chance of overcast or mostly cloudy conditions is 57%, while on July 21, the clearest day of the year, the chance of clear, mostly clear, or partly cloudy skies is 85%.
Cloud Cover Categories in September
A wet day is one with at least 0.04 inches of liquid or liquid-equivalent precipitation. In Porto, the chance of a wet day over the course of September is very rapidly increasing, starting the month at 11% and ending it at 26%.
For reference, the year's highest daily chance of a wet day is 38% on October 29, and its lowest chance is 5% on July 24.
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 Porto is very rapidly increasing, starting the month at 1.1 inches, when it rarely exceeds 2.7 inches or falls below 0.1 inches, and ending the month at 3.3 inches, when it rarely exceeds 6.3 inches or falls below 0.6 inches.
Average Monthly Rainfall in September
Over the course of September in Porto, 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, 18 minutes, implying an average daily decrease of 2 minutes, 42 seconds, and weekly decrease of 18 minutes, 52 seconds.
The shortest day of the month is September 30, with 11 hours, 48 minutes of daylight and the longest day is September 1, with 13 hours, 6 minutes of daylight.
Hours of Daylight and Twilight in September
The earliest sunrise of the month in Porto is 7:01 AM on September 1 and the latest sunrise is 29 minutes later at 7:30 AM on September 30.
The latest sunset is 8:06 PM on September 1 and the earliest sunset is 49 minutes earlier at 7:17 PM on September 30.
Daylight saving time is observed in Porto 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 6:01 AM and sets 15 hours, 9 minutes later, at 9:10 PM, while on December 21, the shortest day of the year, it rises at 7:56 AM and sets 9 hours, 12 minutes later, at 5:08 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 Porto is gradually decreasing during September, falling from 7% to 3% over the course of the month.
For reference, on August 14, 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
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 Porto is essentially constant during September, remaining within 0.1 miles per hour of 3.2 miles per hour throughout.
For reference, on December 27, the windiest day of the year, the daily average wind speed is 4.3 miles per hour, while on September 13, the calmest day of the year, the daily average wind speed is 3.1 miles per hour.
The lowest daily average wind speed during September is 3.1 miles per hour on September 13.
Average Wind Speed in September
Wind Direction in September
Porto 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 Porto is essentially constant during September, remaining around 64°F throughout.
Average Water Temperature 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 Porto is rapidly decreasing during September, falling by 1.8 kWh, from 6.1 kWh to 4.3 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 Porto are 41.150 deg latitude, -8.611 deg longitude, and 272 ft elevation.
The topography within 2 miles of Porto contains significant variations in elevation, with a maximum elevation change of 571 feet and an average elevation above sea level of 272 feet. Within 10 miles contains significant variations in elevation (1,247 feet). Within 50 miles contains very significant variations in elevation (4,695 feet).
The area within 2 miles of Porto is covered by artificial surfaces (90%), within 10 miles by artificial surfaces (31%) and water (28%), and within 50 miles by water (41%) and trees (27%).
This report illustrates the typical weather in Porto 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 2 weather stations near enough to contribute to our estimation of the temperature and dew point in Porto.
For each station, the records are corrected for the elevation difference between that station and Porto 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 Porto is computed as the weighted average of the individual contributions from each station, with weights proportional to the inverse of the distance between Porto and a given station.
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.