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 Atherton: The hottest months are usually December and November, with an average temperature of 24°C, while the coldest months are August and July, with an average of 19°C. The rainiest months in Atherton are January, February, March and December, with each month seeing an average of 229 mm of rainfall.