The hottest month in Sumatra is October when the average maximum temperature is 33°, average temperature is 28° and average minimum temperature is 22°.
The coolest month in Sumatra is September when the average maximum temperature is 33°, average temperature is 28° and average minimum temperature is 22°.
The longest days in Sumatra are in January, with an average of 12.3 hours of daylight per day. May has the shortest days with an average of 12 hours of daylight per day.
The sunniest days in Sumatra are in August which has the most hours of sunshine per day with an average of 9.5 hours of sunshine per day, making it a sunny month with few clouds. December has the least sunshine with an average of 6.4 hours of sunshine per day, making it a quite sunny month with some cloud cover.
The ultraviolet index is the highest in March when it reaches 15.7 and lowest in June when it reaches 11.3.
An ultraviolet index reading above 11 indicates an extreme risk of harm from unprotected sun exposure. Unprotected skin risks burning in less than 10 minutes. Take all precautions because unprotected skin and eyes can burn in minutes. Tanning will be safest before 10am and after 4pm but only with a good application of sun screen. For those with sensitive skin stay in the shade and wear protective clothing, a wide-brimmed hat, and UV-blocking sunglasses. Generously apply broad spectrum SPF 30+ sunscreen every 2 hours, even on cloudy days. Watch out for relections from water that may increase ultraviolet exposure.
The warmest sea water temperatures in Sumatra are found in April when they peak at 30° and lowest in January when they dip to 28°.
The sea is excellent for swimming all year round as the water temperature is very warm and ideal for relaxing and swimming for the whole day.
The wettest month in Sumatra is November with 88.7cm of rain and December has the most days of rain with 25.8 days with some rain, a very wet time to visit the beach.
The driest month in Sumatra is September with 2.7cm of rain and the least days of rain with 6.2 days with some rain, a dry time to visit the beach.
The most humid month in Sumatra is May with a dew point (an indicator of humidity) of 26° which is very uncomfortable and fairly oppressive unless you are on a beach. At night you would most likely require airconditioning.
The least humid month in Sumatra is September with a dew point of 23° which is very humid and quite uncomfortable for most unless you are on a beach. At night you would most likely require a fan.
The most windy month in Sumatra is September when the average maximum windspeed is 27kmh and the average wind speed is 8kmh.
The least windy month in Sumatra is November when the average maximum windspeed is 16kmh and the average wind speed is 3kmh.