Climate in Sumatra

Average daytime and nighttime temperatures

All climate diagrams on this site result from the collected data from 33 measuring weather stations in Sumatra.
Weather stations at an altitude above 780m have not been included.
All data correspond to the average monthly values of the last 20 years.

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Sumatra is one of the coldest regions in Indonesia with an average daily high temperature of only 32 degrees. High humidity and hot temperatures make the weather pleasant at times but also tropical humid. It is warm to hot all year round, inviting bathing at average water temperatures of 29 degrees. Due to less rain, the best time for traveling is in February. Most precipitation falls from November to December.
Overview: Climate in Indonesia
Daylengths and sun positions in Indonesia
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Sunshine hours per day
The number of hours of sunshine refers to the time when the sun is actually visible. That is, without any obstruction of visibility by clouds, fog or mountains. With 6 hours per day, July is the sunniest month in archipelago Sumatra. In December, the sun shines the least.
Rain days per month
A rain day is a day on which at least 0.1 mm precipitation (=0.1 liter) per square meter falls. This can be rain, snow, hail or even dew. So it does not have to rain the whole day. With 18 rain days, November offers the most rain days, while February has the fewest.
Precipitation amount in mm/day
The amount of precipitation is measured in millimeters per square meter. Thus, at two mm/day, two liters of water fall on one square meter within 24 hours. With only 5.4 mm, the least amount of rain falls in July. November, on the other hand, has the most rain.
Water temperatures in °C
Water temperature depends not only on solar radiation within the same region, but also on ocean currents. For example, depending on the season, cold or warm water masses are moved from other areas. The warmest water temperatures in Sumatra are in June, when the water is 29 °C.
Relative humidity in %
Warm air can absorb more moisture than cold air. The relative humidity indicates how much moisture can be physically contained in the air. At high humidity, a person feels uncomfortable and perceives this as oppressive. In general, a relative humidity of 40-60% feels pleasant. With humidity averaging 86%, November is the most uncomfortable. In February, on the other hand, it is easier to endure.
Absolute humidity in g/m³
In warm months, there is also a higher absolute humidity almost everywhere. At a temperature of 25°C, air can absorb up to 23 grams of water per cubic meter. At 20°C, it is only 17.3 grams. A relative humidity of 40% at 25°C thus corresponds to an absolute humidity of 9.2 grams of water. From a proportion of approx. 13.5 grams, humans perceive the air as muggy. This limit is exceeded throughout the year in Sumatra.
The "Humidex" (humidity index) is an index of well-being in warmer areas, calculated from the air temperature, relative humidity and dew point. The index corresponds approximately to the temperature felt. At high temperatures, the body transports heat away by sweating. At high humidity, the ambient air can only absorb a small amount of sweat and thus one feels uncomfortable. An index of 20-29 is considered comfortable. Up to 39, people perceive the air as slightly uncomfortable, and above 40, as very uncomfortable. Values above 45 are dangerous in the long run and often lead to heat stroke.
Climate charts for other archipelagos in Indonesia

Map of Sumatra

Most important cities in the archipelago »Sumatra«

Alone 6 major cities with over 500,000 inhabitants are located here. The archipelago has a west-east extension of about 1440 km and over 1260 km from north to south.

It consists of the nine provinces Aceh, Bangka-Belitung, Bengkulu, Jambi, Lampung, North Sumatra, Riau, South Sumatra and West Sumatra.

CityPopulationGeo position
Medan2,435,2523° 34' 60"N98° 40' 0"E
Palembang1,662,8932° 55' 0"S104° 44' 45"E
Bandarlampung923,9705° 25' 32"S105° 15' 29"E
Padang876,8800° 56' 57"S100° 21' 15"E
Pekanbaru703,9560° 31' 60"N101° 27' 0"E
Jambi City586,9301° 36' 0"S103° 37' 0"E
Percut311,0633° 37' 31"N98° 51' 50"E
Bengkulu308,5443° 48' 2"S102° 15' 56"E
Binjai246,1543° 36' 0"N98° 29' 7"E
Banda Aceh223,4465° 33' 28"N95° 19' 20"E
Pematangsiantar209,6142° 57' 34"N99° 4' 7"E
Sunggal157,9143° 34' 35"N98° 36' 54"E
Perbaungan157,1743° 34' 4"N98° 57' 22"E
Metro149,5265° 6' 47"S105° 18' 24"E
Lubuklinggau148,2433° 17' 40"S102° 51' 41"E
Dumai143,7601° 40' 2"N101° 26' 35"E
Tanjungbalai142,5062° 58' 0"N99° 47' 60"E
Baturaja134,7594° 7' 44"S104° 10' 1"E
Kisaran129,9112° 59' 4"N99° 36' 57"E
Pangkalpinang125,9332° 7' 45"S106° 6' 50"E
Payakumbuh121,5720° 12' 57"S100° 38' 0"E
Tebingtinggi117,5303° 19' 43"N99° 9' 45"E
Prabumulih103,4703° 26' 4"S104° 13' 50"E
Rantauprapat103,0092° 6' 0"N99° 49' 60"E
Belawan102,7073° 46' 32"N98° 40' 60"E
Padangsidempuan100,5611° 22' 46"N99° 16' 17"E
Bukittinggi98,7460° 18' 33"S100° 22' 14"E
Sungai Penuh95,9132° 3' 22"S101° 23' 29"E
Pariaman92,1830° 37' 8"S100° 7' 12"E
Lhokseumawe88,9745° 10' 48"N97° 9' 3"E

Data basis: German Weather Service, individual values averaged and supplemented by own elements. Data on cities and inhabitants:, United Nations Statistics Division and own research.
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