If you're hoping to get lost in the rain on your romantic getaway, take a look at these details about year-round temperatures in Monrovia: The hottest months are usually January and April, with an average temperature of 27°C, while the coldest months are August and September, with an average of 25°C. The rainiest months in Monrovia are September, June, August and July, with each month seeing an average of 608 mm of rainfall.