...and more
In terms of precipitation, rainfall in Surabaya ranges from 0.4 - 11.0 inches per month. January is typically the wettest month, when rainfall can reach 11.0 in. August is typically the driest time to visit Surabaya when rainfall is around 0.4 in.
If weather is an important factor for your trip to Surabaya, use this chart to help with planning. For those seeking warmer temperatures, October is the ideal time of year to visit, when temperatures reach an average of 84.2 F. Travelers looking to avoid the cold should look outside of January, when temperatures are typically at their lowest (around 80.6 F).