If you’re looking forward to lots of outings with your partner, check out these details about year-round temperatures in Ong Lang: The hottest months are usually May and April with an average temp of 83°F, while the coldest months are January and December with an average of 81°F. The rainiest months in Ong Lang are September, July, October, and August, with each month seeing an average of 13 inches of rainfall.