singapore and hongkong will be very very hot! somewhere around 28 degrees c for singapore, and i expect hongkong would be the same.
in singapore it's much more humid, so the weather can be quite unbearable at times. bring/buy a spritzer. otherwise u can make one yourself:
get a small spritzer bottle
fill it with water
add abt 2-3 drops of facial toner
hope the weather won't be too uncomfortable for u, but south east asia pretty much experiences the same weather throughout that time of the year. i think some parts in thailand may be cooler but that might be the southern parts. the norther parts are really hot in the middle of the year. i went to chiang mai in april or so, and it was about 37 degrees c!