Algiers: Annual Weather Averages. August is the hottest month in Algiers with an average temperature of 26°C (79°F) and the coldest is January at 11°C (52°F) with the most daily sunshine hours at 11 in July. The wettest month is December with an average of 103mm of rain.ugust is the hottest month in Algiers with an average temperature of 26°C (79°F) and the coldest is January at 11°C (52°F) with the most daily sunshine hours at 11 in July.