The rainy season is fairly ghastly and you can expect to be wet most of the time. Luckily, it only lasts six to eight weeks. The climate is generally quite livable in Miyazaki. For those of you coming from that soggy island off the west coast of continental Europe and similar climates, it will seem pretty good. As a generalization, in the summer it's hot and sticky, in the winter it's cold and fairly dry.
Autumn is long, warm and dry and spring is changeable.
Just let common sense prevail in your estimation of the geographical variations in the climate, i.e., the mountains get colder sooner. From a female standpoint, I have one remark in regards to the hot weather. For those females going to more rural towns, I suggest exercising discretion in choosing summer garments. Yes, it's hot. Yes, it's humid.