100 ozs is around 3 liters = 6 lbs, which is a full load of water for most people. Water needs vary somewhat for each individual so think about how you compare with "average" hikers you might know. I'm reluctant to advise you to bring less water, but you'll probably do just fine with 2 liters between the Portal and Trail Camp. It's usually enough and you have a few things working for you, it will be cooler that average in October and you'll probably be hiking up to Trail Camp at night and early morning. And of course it's downhill on the way back when it's the warmest part of the day. The key stretch is the summit bid going up from Trail Camp and then back down to refill. Three liters is about right for that round trip, in my opinion. Be sure to drink a good amount at the Portal before you hit the trail and camel up again when you're refilling at Trail Camp each time. Have a great adventure!
