Average Weather In September For Cape Town, South Africa

Location

This report describes the typical weather at the Cape Town International Airport (Cape Town, South Africa) weather station over the course of an average September. It is based on the historical records from 1994 to 2012. Earlier records are either unavailable or unreliable.

Cape Town has a mediterranean climate with dry warm summers and mild winters. The area within 25 mi of this station is covered by oceans and seas (40%), grasslands (33%), croplands (17%), built-up areas (6%), and forests (5%).

Temperature

The month of September is characterized by gradually rising daily high temperatures, with daily highs increasing from 64°F to 68°F over the course of the month, exceeding 76°F or dropping below 59°F only one day in ten.

Daily High and Low Temperature in September

The daily average low (blue) and high (red) temperature with percentile bands (inner band from 25th to 75th percentile, outer band from 10th to 90th percentile).
Daily low temperatures are around 49°F, falling below 42°F or exceeding 56°F only one day in ten.

Fraction of Time Spent in Various Temperature Bands in September

The average fraction of time spent in various temperature bands: frigid (below 15°F), freezing (15°F to 32°F), cold (32°F to 50°F), cool (50°F to 65°F), comfortable (65°F to 75°F), warm (75°F to 85°F), hot (85°F to 100°F) and sweltering (above 100°F).

Sun

Over the course of September, the length of the day is increasing. From the start to the end of the month, the length of the day increases by 1:00 hours, implying an average day-over-day increase of 2.0 minutes.

The shortest day of the month is September 1 with 11:24 hours of daylight; the longest day is September 30 with 12:24 hours of daylight.

Daily Hours of Daylight and Twilight in September

The number of hours during which the Sun is visible (black line), with various degrees of daylight, twilight, and night, indicated by the color bands. From bottom (most yellow) to top (most gray): full daylight, solar twilight (Sun is visible but less than 6° from the horizon), civil twilight (Sun is not visible but is less than 6° below the horizon), nautical twilight (Sun is between 6° and 12° below the horizon), astronomical twilight (Sun is between 12° and 18° below the horizon), and full night.

The earliest sunrise is at 6:24am on September 30; the latest sunset is at 6:48pm on September 30; the latest sunrise is at 7:04am on September 1; the earliest sunset is at 6:28pm on September 1.

Daylight savings time (DST) is not observed in 2012.

Daily Sunrise & Sunset with Twilight in September

The solar day over the course of the year 2012 . From bottom to top, the black lines are the previous solar midnight, sunrise, solar noon, sunset, and the next solar midnight. The day, twilights (solar, civil, nautical, and astronomical), and night are indicated by the color bands from yellow to gray.

Clouds

The median cloud cover ranges from 43% (partly cloudy) to 53% (partly cloudy). The trend is for the sky to be clearing with the median cloud cover decreasing by 10% from the start to the end of the month.

Median Cloud Cover in September

The median daily cloud cover (black line) with percentile bands (inner band from 40th to 60th percentile, outer band from 25th to 75th percentile).

On September 30, the clearest day of the month, the sky is clear, mostly clear, or partly cloudy 59% of the time, and overcast or mostly cloudy 29% of the time.

On September 1, the cloudiest day of the month, the sky is overcast, mostly cloudy, or partly cloudy 47% of the time, and clear or mostly clear 40% of the time.

Cloud Cover Types in September

The fraction of time spent in each of the five sky cover categories. From top (most blue) to bottom (most gray), the categories are clear, mostly clear, partly cloudy, mostly cloudy, and overcast. Pink indicates missing data. Outside of the United States clear skies are often reported ambiguously, leading them to be lumped in with the missing data.

Precipitation

The probability that precipitation will be observed at this location varies throughout the month. Precipitation is most likely around September 1, occurring in 41% of days. Precipitation is least likely around September 30, occurring in 35% of days.

Probability of Precipitation at Some Point in the Day in September

The fraction of days in which various types of precipitation are observed. If more than one type of precipitation is reported in a given day, the more severe precipitation is counted. For example, if light rain is observed in the same day as a thunderstorm, that day counts towards the thunderstorm totals. The order of severity is from the top down in this graph, with the most severe at the bottom.

Throughout September, the most common forms of precipitation are moderate rain and light rain.

Moderate rain is the most severe precipitation observed during 51% of those days with precipitation. It is most likely around September 1, when it is observed during 22% of all days.

Light rain is the most severe precipitation observed during 41% of those days with precipitation. It is most likely around September 9, when it is observed during 17% of all days.

Types of Precipitation Throughout September

Relative frequency of various types of precipitation over the course of a typical September.

Snow

Either snow is exceptionally unlikely to fall at this location in September or this station does not reliably report precipitation types.

Humidity

The relative humidity typically ranges from 49% (comfortable) to 96% (very humid) over the course of a typical September, rarely dropping below 34% (comfortable) and reaching as high as 100% (very humid).

The air is driest around September 29, at which time the relative humidity drops below 57% (mildly humid) three days out of four; it is most humid around September 1, rising above 93% (very humid) three days out of four.

Relative Humidity in September

The average daily high (blue) and low (brown) relative humidity with percentile bands (inner bands from 25th to 75th percentile, outer bands from 10th to 90th percentile).

Dew Point

Dew point is often a better measure of how comfortable a person will find the weather than relative humidity because it more directly relates to whether perspiration will evaporate from the skin, thereby cooling the body. Lower dew points feel drier and higher dew points feel more humid.

Over the course of a typical September, the dew point typically varies from 43°F (dry) to 54°F (very comfortable) and is rarely below 37°F (dry) or above 58°F (comfortable).

The time of the month between September 1 and September 30 is the most comfortable, with dew points that are neither too dry nor too muggy.

Dew Point in September

The daily average low (blue) and high (red) dew point with percentile bands (inner band from 25th to 75th percentile, outer band from 10th to 90th percentile).

Wind

Over the course of September typical wind speeds vary from 2 mph to 19 mph (light air to fresh breeze), rarely exceeding 27 mph (strong breeze).

The highest average wind speed of 11 mph (gentle breeze) occurs around September 30, at which time the average daily maximum wind speed is 19 mph (fresh breeze).

The lowest average wind speed of 10 mph (gentle breeze) occurs around September 2, at which time the average daily maximum wind speed is 18 mph (fresh breeze).

Wind Speed in September

The average daily minimum (red), maximum (green), and average (black) wind speed with percentile bands (inner band from 25th to 75th percentile, outer band from 10th to 90th percentile).
The wind is most often out of the south (32% of the time), north west (14% of the time), north (13% of the time), and south west (12% of the time). The wind is least often out of the east (2% of the time), north east (5% of the time), and west (5% of the time).

Wind Directions in September

The fraction of time spent with the wind blowing from the various directions over the entire year. Values do not sum to 100% because the wind direction is undefined when the wind speed is zero.

Fraction of Time Spent with Various Wind Directions in September

The fraction of time spent with the wind blowing from the various directions on a daily basis. Stacked values do not always sum to 100% because the wind direction is undefined when the wind speed is zero.