Rafting down the Li River on the way to Yangshuo in southwest China. Photo by Jemielniak.
Asia is a huge area with varied climates but here are some idea of what you can expect in some popular tourist zones in September-October. Generally monsoon rains are slackening off and heat level is becoming acceptable though humidity may be oppressive. Not generally a good time for tourism in Asia.
October is likely to be cooler, drier and less humid.
China: Autumn is spreading across this vast country, with drier, pleasant weather moving down from the north though the south is still sticky and getting substantial rain. Beijing normally experiences temperatures of 16°C–26°C (61°F–79°F), with 8 days of rain in the month while Shanghai will be hotter and wetter. October should be an improvement.
Indonesia: At last! A place with favourable weather conditions, in the first half of the month anyway. Temperatures can reach the low 30C’s (mid 80F’s).
Tibet: Good season, still warm, not much rain, autumn colours spreading. Excellent for trekking.
Nepal: Best weather towards the end of the month with blue skies and temperatures in the mid 20C’s (high 60F’s). Excellent for trekking.