| Month | High | Low | Rain | Wet days | Score |
|---|---|---|---|---|---|
| January | 10.3° | — | 49.8mm | 7.6 | 54 |
| February | 12° | — | 86mm | 9 | 56 |
| March | 15.9° | — | 115.4mm | 10.6 | 66 |
| April | 20.9° | — | 162.2mm | 9.7 | 81 |
| May | 25.8° | — | 180.4mm | 9.2 | 82 |
| June | 28.3° | — | 298.7mm | 13.3 | 68 |
| July | 31.9° | — | 386mm | 13.4 | 54 |
| August | 33.1° | — | 299.4mm | 12.2 | 51 |
| September | 29.5° | — | 176mm | 11.3 | 67 |
| October | 24.5° | — | 107.9mm | 6.6 | 87 |
| November | 18.5° | — | 80.2mm | 7.6 | 80 |
| December | 12.5° | — | 60.8mm | 8.4 | 59 |
January in Karatsu averages a daily high of 10.3°C. Expect roughly 7.6 wet days totalling 49.8mm. Demanding conditions — pack for it and plan indoor options.
February in Karatsu averages a daily high of 12°C. Expect roughly 9 wet days totalling 86mm. Generally workable, with some weather to plan around.
March in Karatsu averages a daily high of 15.9°C. Expect roughly 10.6 wet days totalling 115.4mm. Generally workable, with some weather to plan around.
April in Karatsu averages a daily high of 20.9°C. Expect roughly 9.7 wet days totalling 162.2mm. Comfortable conditions for being outdoors all day.
May in Karatsu averages a daily high of 25.8°C. Expect roughly 9.2 wet days totalling 180.4mm. Comfortable conditions for being outdoors all day.
June in Karatsu averages a daily high of 28.3°C. Expect roughly 13.3 wet days totalling 298.7mm. Generally workable, with some weather to plan around.
July in Karatsu averages a daily high of 31.9°C. Expect roughly 13.4 wet days totalling 386mm. Demanding conditions — pack for it and plan indoor options.
August in Karatsu averages a daily high of 33.1°C. Expect roughly 12.2 wet days totalling 299.4mm. Demanding conditions — pack for it and plan indoor options.
September in Karatsu averages a daily high of 29.5°C. Expect roughly 11.3 wet days totalling 176mm. Generally workable, with some weather to plan around.
October in Karatsu averages a daily high of 24.5°C. Expect roughly 6.6 wet days totalling 107.9mm. Comfortable conditions for being outdoors all day.
November in Karatsu averages a daily high of 18.5°C. Expect roughly 7.6 wet days totalling 80.2mm. Comfortable conditions for being outdoors all day.
December in Karatsu averages a daily high of 12.5°C. Expect roughly 8.4 wet days totalling 60.8mm. Generally workable, with some weather to plan around.
Each month scores out of 100. It starts at 100 and loses points for daytime highs outside a 20–27°C band, for wet days, and for nights below 2°C. Nothing else is weighted in — no crowd data, no prices, no opinion. Karatsu peaks at 87.
Based on 30 years of records, April–May scores highest for comfort in Karatsu, balancing daytime temperature against rainfall.
August is the warmest, averaging a daily high of 33.1°C.
July is the wettest, averaging 386mm of rain across roughly 13.4 wet days.
January is the coolest month, with average daily highs around 10.3°C.