April to early May and October to early November are generally transitional or changeover months separating monsoons. The mean annual rainfall is 2360 mm. December is generally the wettest month of the year with an average monthly rainfall of 280 mm, while July is the month with lowest average monthly rainfall of 160 mm. The Northeast monsoon winds are generally cooler and more constant in direction and bring spells of wet weather which may persist for several days at a time. The wet spells are more frequent during the first three months of the North-east monsoon season.
Dry spells occur during the later part of each monsoon season.
These squalls consists of gusty winds occasionally strong, often accompanied by heavy rain and thunder with drops in temperature, but the more intense features of the storm seldom last for more than one hour. The highest recorded wind speed during a Sumatra is 114 kilometres per hour. During the changeover months of April and October, winds are light and variable in direction. Afternoon or evening thunderstorms and conventional showers are more frequent.