weather in Tuscany...Sept-Oct

Yes, of course especially in early Sep but late Oct can be very nice. Inbetween ??? Who knows??

I've only been to Tuscany twice, once in late Sept and once in early Oct. Both times the weather was ideal. It was warm but not hot, think upper 70's low 80's during the day, 50's-60's at night. I certainly don't remember humidity being an issue, actually it was quite dry, never had any rain on either trip. That's only my experience so take it for what it's worth. Weather is so hard to predict even using the historical averages won't guarantee you good weather. I have read lots of posters on this forum stating that they think Sept-Oct is the best time of year to go to Italy in general and Tuscany in particular.

Even in the heart of summer it never gets as humid as the weather back East (including Virginia). There are days in summer when it's a bit more humid, but generally Mediterranean weather is fairly dry.
It's hard to predict the weather so far ahead.
Generally early September can be hot as in August, but no guarantee. Some years it gets cooler earlier and rain is possible.
October is generally not hot, just warm during the day, but cool at night and early morning. Rain is likely in October, particularly the second half of the month. The second half of October and the first of November is the rainiest time of the year (on average). The great floods of the river Arno of 1844, 1944 and 1966 happened on Nov 3, Nov 2 and Nov 4, respectively.
As I said it's hard to predict, some years the weather stays warm all month with not too much rain, some other year October is rainy all the time and very cool.