This report describes the typical weather at the Amsterdam Airport Schiphol (Amsterdam, The Netherlands) weather station over the course of an average September. It is based on the historical records from 1974 to 2012. Earlier records are either unavailable or unreliable.
Amsterdam has a mild humid temperate climate with warm summers and no dry season. The area within 25 mi of this station is covered by croplands (62%), oceans and seas (27%), and built-up areas (8%).
The month of September is characterized by falling daily high temperatures, with daily highs decreasing from 68°F to 62°F over the course of the month, exceeding 75°F or dropping below 56°F only one day in ten.
Over the course of September, the length of the day is rapidly decreasing. From the start to the end of the month, the length of the day decreases by 1:55 hours, implying an average day-over-day decrease of 3.8 minutes.
The shortest day of the month is September 30 with 11:39 hours of daylight; the longest day is September 1 with 13:34 hours of daylight.
The earliest sunrise is at 6:53am on September 1; the latest sunset is at 8:27pm on September 1; the latest sunrise is at 7:41am on September 30; the earliest sunset is at 7:19pm on September 30.
Daylight savings time is observed in 2012 but it neither starts nor ends in September, so the entire month is in daylight time.
The median cloud cover ranges from 60% (partly cloudy) to 70% (partly cloudy). The trend is for the sky to be becoming cloudier with the median cloud cover increasing by 10% from the start to the end of the month.
On September 15, a representative day, the sky is clear or mostly clear 36% of the time, partly cloudy 20% of the time, and mostly cloudy or overcast 40% of the time.
The average probability that some form of precipitation will be observed in a given day is 66%, with little variation over the course of the month.
Throughout September, the most common forms of precipitation are moderate rain, thunderstorms, and light rain.
Moderate rain is the most severe precipitation observed during 66% of those days with precipitation. It is most likely around September 25, when it is observed during 45% of all days.
Thunderstorms are the most severe precipitation observed during 16% of those days with precipitation. They are most likely around September 2, when it is observed during 11% of all days.
Light rain is the most severe precipitation observed during 11% of those days with precipitation. It is most likely around September 16, when it is observed during 8% 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 62% (mildly humid) to 97% (very humid) over the course of a typical September, rarely dropping below 50% (comfortable) and reaching as high as 100% (very humid).
The air is driest around September 1, at which time the relative humidity drops below 69% (mildly humid) three days out of four; it is most humid around September 30, rising above 94% (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 47°F (dry) to 59°F (comfortable) and is rarely below 41°F (dry) or above 64°F (mildy humid).
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 3 mph to 16 mph (light air to moderate breeze), rarely exceeding 25 mph (strong breeze).
The highest average wind speed of 10 mph (gentle breeze) occurs around September 30, at which time the average daily maximum wind speed is 16 mph (moderate breeze).
The lowest average wind speed of 10 mph (gentle breeze) occurs around September 1, at which time the average daily maximum wind speed is 15 mph (moderate breeze).