Karatsu's climate is marked by a gradual warming trend throughout the year, with cold winters giving way to mild springs and hot summers. The winter months, January and February, bring frosty temperatures ranging from -4°C to 20°C, while spring arrives in March with temperatures rising to an average of 13°C. As summer sets in, June and July are the warmest months, with highs reaching up to 35°C and 36°C respectively. Autumn brings a welcome respite from the heat, with September's average temperature still relatively high at 25°C, before cooling down to more moderate levels by November. The winter chill returns in December, with temperatures dipping back to around -3°C.