Winters in Iwanuma are cold and unpredictable, with temperatures fluctuating wildly between sub-zero lows and mild highs. Spring brings gradual warming, with March marking a significant increase in average temperature, while April sees temperatures rise further, but still experiencing occasional chilly mornings. Summer is hot and humid, with July and August often reaching scorching highs above 35°C. Autumn is mild to warm, with September being the hottest month of the season, followed by a gentle cooling trend into October.