This report describes the typical weather at the Tromsø Airport (Tromsø, Norway) 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.
Tromsø has a humid subarctic continental climate with cool summers and no dry season. The area within 25 mi of this station is covered by tundra (47%), oceans and seas (36%), and forests (14%).
The month of September is characterized by falling daily high temperatures, with daily highs decreasing from 54°F to 46°F over the course of the month, exceeding 61°F or dropping below 39°F only one day in ten.
Over the course of September, the length of the day is very rapidly decreasing. From the start to the end of the month, the length of the day decreases by 4:07 hours, implying an average day-over-day decrease of 8.2 minutes.
The shortest day of the month is September 30 with 11:12 hours of daylight; the longest day is September 1 with 15:19 hours of daylight.
The earliest sunrise is at 5:03am on September 1; the latest sunset is at 8:23pm on September 1; the latest sunrise is at 6:57am on September 30; the earliest sunset is at 6:09pm 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 is 88% (mostly cloudy) and does not vary substantially over the course of the month.
On September 15, a representative day, the sky is clear or mostly clear 17% of the time, partly cloudy 20% of the time, and mostly cloudy or overcast 57% of the time.
The probability that precipitation will be observed at this location varies throughout the month. Precipitation is most likely around September 30, occurring in 77% of days. Precipitation is least likely around September 1, occurring in 71% 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 64% of those days with precipitation. It is most likely around September 15, when it is observed during 49% of all days.
Light rain is the most severe precipitation observed during 18% of those days with precipitation. It is most likely around September 4, when it is observed during 15% of all days.
The likelihood of snow falling is highest around September 30, occurring in 18% of days.
Either snow rarely accumulates at this location in September or snow depth measurements are unavailable or unreliable.
The relative humidity typically ranges from 64% (mildly humid) to 94% (very humid) over the course of a typical September, rarely dropping below 50% (mildly humid) and reaching as high as 100% (very humid).
The air is driest around September 4, at which time the relative humidity drops below 72% (humid) three days out of four; it is most humid around September 9, rising above 92% (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 32°F (dry) to 46°F (dry) and is rarely below 24°F (dry) or above 52°F (very comfortable).
Over the course of September typical wind speeds vary from 0 mph to 15 mph (calm to moderate breeze), rarely exceeding 24 mph (strong breeze).
The highest average wind speed of 8 mph (gentle breeze) occurs around September 30, at which time the average daily maximum wind speed is 15 mph (moderate breeze).
The lowest average wind speed of 6 mph (light breeze) occurs around September 4, at which time the average daily maximum wind speed is 13 mph (moderate breeze).