...and more
In terms of precipitation, rainfall in Sumatra ranges from 3.1 - 10.6 inches per month. October is typically the wettest month, when rainfall can reach 10.6 in. February is typically the driest time to visit Sumatra when rainfall is around 3.1 in.
If weather is an important factor for your trip to Sumatra, use this chart to help with planning. For those seeking warmer temperatures, February is the ideal time of year to visit, when temperatures reach an average of 80.6 F. Travelers looking to avoid the cold should look outside of January, when temperatures are typically at their lowest (around 78.8 F).