Shall be in Kyoto-Hiroshima-Nagoya-Tokyo from 10th September to 22nd September. What will the weather be like ?

most likely nice weather, but it could be unseasonably warm or unseasonably cold.

http://www.wunderground.com/NORMS/Di...&Units=english

More likely hot than "cold." Could be as high as 30 degrees, but probably no lower than 20 (i.e., in F, from 70 to mid-80s). High humidity can still be unpleasant. We arrived in the Osaka region of Kansai last September 12th, and had some very hot and humid days (and nights) before October came.

September is also the main typhoon season, and you can expect at least one or two typhoons to hit Japan during your stay. It may not disrupt your stay too much, depending on the course the typhoon follows, but typically, they come up from Okinawa and hit the mainland somewhere between Kyushu, Shikoku and Kii Peninsula south of Osaka. If you get a direct hit, it means high wind and heavy rain for 24 hours, and seriously disrupts your travel plan, as trains etc usually stop or services are heavily curtailed. If you miss it, it may still rain heavily but disruption will be less.

Thanks for all your replies

Is it sensible to carry raincoats/umbrellas around? Coming from a tinder-dry Australia, rain would be a nice relief.

Check here for current Japan weather information.

http://www.jma.go.jp/jma/indexe.html

In twelve days on the ground you should encounter rain somewhere. If its a typhoon, umbrellas won't help, stay indoors. If its casual rain, you will see umbrellas stands popping up in all shops and on street corners everywhere from 400 yen and up.

That said El Nino has arrived here in the Pacific changing regular weather patterns to El Nino ones. You can check here for a few details. Check the English pdf version

http://www.cpc.ncep.noaa.gov/product...enso_advisory/


Aloha!

Coming from the desert known as Los Angeles and not owning any rain-gear, I bought a nice compact umbrella after I got to Tokyo a few weeks ago. Definitely needed it.