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