Other facts from our historical weather data: Which months have the greatest rainfall in Onitsha? Most rainfall (rainy season) is seen in May, June, July, August, September and October. Does Onitsha have a dry season? Yes, the months of January and December are very dry. Which is the hottest month in Onitsha? February has an average maximum temperature of 37°C (99°F) and is the hottest month of the year. Which is the coolest month in Onitsha? The coolest month is August with an average maximum temperature of 30°C (86°F). Which is the wettest month in Onitsha? September tops the wettest month list with 227mm (8.9 in) of rainfall. Which is the driest month in Onitsha? December is the driest month with 10mm (0.4 in) of precipitation. No idea where to travel to this year? We have a tool that recommends destinations based on your ideal conditions. Find out where to go with our weather planner.