Map from Google - Fukuoka

The climate of Fukuoka, a Japanese city located on the north coast of Kyushu, the southernmost of the major Japanese islands, is temperate humid, with quite mild winters and hot, moist, and rainy summers. Like the rest of Japan, the city is affected by the monsoon circulation: in winter the northwest cold currents will prevail, while in summer they will be replaced by the hot and humid currents of tropical origin.
The city is located at a low latitude (we are at the 33rd parallel), but close enough to the Asian continent to be received in winter by cold air masses, able to lower the temperature.
In the winter the sky is often cloudy, as is common in the Japanese western side; there are fairly mild periods, with highs above 10 °C (50 °F), alternating with cold periods, with wind and rain, highs around 5/7 °C (41/45 °F) or less, and possible falls of sleet or snow. Snowfalls, however, are generally light, as are nocturnal frosts.
Summers are hot and humid; there can be periods of good weather, with maximum temperatures around 35 °C (95 °F), tropical nights and high humidity, but also periods of bad weather, due to the summer monsoon. August is the hottest month, both for the thermal inertia of the sea, and for the lower frequency of periods of bad weather.
Here are the average temperatures.
Average temperatures - Fukuoka
FukuokaJanFebMarAprMayJunJulAugSepOctNovDec
FukuokaJFMAMJJASOND
Min (°C)44711162024252115106
Max (°C)101114202427313228231813
Min (°F)393945526168757770595043
Max (°F)505257687581889082736455

The rains are abundant, as they amount to 1,600 millimetres (63 inches) per year; winter is the driest season, but only in quantity; the rainiest months are June and July, ie the first period of the rainy season (called Baiu), which in southern Japan is particularly marked. In August there is a certain decrease in the frequency of the rains: on average, among the summer months, it is the hottest, as well as the driest and sunniest. In the southwest of Japan, autumn is a decent season, and already in October it typically does not rain much.
Here is the average precipitation.
Average precipitation - Fukuoka
FukuokaJanFebMarAprMayJunJulAugSepOctNovDecYear
FukuokaJFMAMJJASONDY
Prec. (mm)70701151151452552801701807585601610
Prec. (in)2.82.84.54.55.710116.77.133.32.463.4
Days11101311111212101171010129

In the latter part of summer and in early autumn, from August to October (though more likely in August and September), Fukuoka may be affected by typhoons, the tropical cyclones of Southeast Asia.
The cherry blossoming in Fukuoka occurs around 28/29 March.
The amount of sunshine in Fukuoka is never very good, however, you can see two peaks, one in spring (April-May), and the other in August, after the Baiu rains, with 6/6.5 hours of sunshine per day. Also in October, after the summer rains, the sunshine amount increases a little.

Fukuoka

The sea in Fukuoka in winter is cold but not impossible for the more daring; it is warm enough for swimming, with a temperature of 23 °C (73 °F) or more, from July to October, and it gets pleasantly warm in August.
Sea temperature - Fukuoka
FukuokaJanFebMarAprMayJunJulAugSepOctNovDec
FukuokaJFMAMJJASOND
Sea (°C)171616182022252726242219
Sea (°F)636161646872778179757266