Just came back from Tokyo, the weather is cooler than HK. I just worn a coat (Autumn knit wear)or denim jacket will do for adult. I took along my goretex but of no use. Actually, just bring along a scraf will help a lot.
For little girl, I will bring along the same. "down" jacket will be a bit too much for my standard of cold and cool.
To me, the weather is great.
Have a nice trip.
If you are interested in Art/ Buildings, make an effort to National Art Centre Tokyo, it is opened only this year. The area is extremely nice, not to mentioned the building itself.
There are so many designer chairs inside for you to "sit" around and enjoy. The gallery shop inside the basement was small but nice. I bought a pair of cufflinks for my husband.