Weather in Onitsha

Onitsha is in Nigeria at 6.1°N. The 2001–2020 NASA POWER daily record describes a monsoon climate with a sharp wet-dry split. March is the warmest month (average 27.2°C, high 30.5°C) and January is the coolest (average 24.6°C, low 19.7°C).

Rain is the monsoon runs from April to October, inside an annual total of 1705 mm. The wettest month is September at 315 mm; the driest is January at 12 mm. On this site the months that score closest to a 22°C day, lighter rain, and moderate humidity are December, January, and February.

When the score favours a visit

The three months with the highest comfort score are December, January, and February: December (25.0°C average, 15 mm, 75% humidity); January (24.6°C average, 12 mm, 72% humidity); February (26.4°C average, 29 mm, 79% humidity). Those months sit across the year end, so they are listed in season order rather than January-to-December. The score rewards averages near 22°C, lower rainfall, and humidity near 60%. It is a climate score, not a festival or price calendar.

If you want the monsoon itself — fewer crowds, greener landscape, heavier rain — aim at April–October instead of the score.

How warm Onitsha gets

The heat peaks in March, when the typical afternoon is 30.5°C. The opposite pole is January, when mornings average 19.7°C.

Across the year the mean afternoon high is 29.3°C. If you want the smallest day–night shock, look at months where the high and low sit close together; March nights still hold 23.8°C.

Rainfall pattern

The monsoon in Onitsha starts in April and ends in October (April, May, June, July, August, September, and October). September is the core of it at 315 mm. January is the other extreme, with 12 mm.

Humidity peaks near 90%. That usually lines up with the wetter months rather than the hottest ones.

The calendar in Onitsha

The year bottoms out in January. Plan for 19.7°C at night and 29.6°C in the afternoon. Peak heat arrives in March: 30.5°C by day, 23.8°C at night, and 85% humidity. April is when the monsoon typically starts in Onitsha: highs near 30.3°C, and rainfall jumps to 123 mm (21 rainy days). June stands apart from the months beside it: 28.6°C / 23.1°C and 227 mm.

September is the wettest month — 315 mm and 29 rainy days, with 90% humidity. By October the monsoon is ending. Onitsha still sees about 210 mm, but the next month is usually leaner. November stands apart from the months beside it: 29.5°C / 22.7°C and 73 mm. December: 29.6°C high, 20.4°C low, 15 mm rain, 75% humidity.

Onitsha and other cities in Nigeria

Benin City is about 130 km away: Onitsha is about as warm as Benin City at the hot peak and a similar annual rainfall (1726 mm in Benin City). Benin City’s wettest month is September (301 mm) versus September here.

Port Harcourt is about 155 km away: Onitsha is about as warm as Port Harcourt at the hot peak and 615 mm drier over the year than Port Harcourt. Port Harcourt’s wettest month is September (397 mm) versus September here.

Abuja is about 333 km away: Onitsha is 2.1°C cooler than Abuja in its hottest month and 521 mm wetter over the year than Abuja. Abuja’s wettest month is August (253 mm) versus September here.