It's the showing of finishing of the plants bud cycle and should be expected .
You want your plant to eat it's leaves at the end of your grow like that . Just make sure you get rid of the unhealthy ones as your plants have plenty of leaf to finsih with . If the leaves are older and dying , get rid of them so all your growth goes to yeild and healthy leaves , rather than old leaves the plant has used up already .
My grow at the end , you've seen the color or my leaves towards the end near harvest time , even after giving my plants Nitrogen to the end , guano and worm castings , still ate their leaves - yellowed at finish time .
It's a good thing and is for flavor reasons I let my plants eat their leaves , as long as it's this far along in stage in budding . Otherwise it would be due to nutrients loss and fixed with guano added . Nitrogen issue .
It's normal for your plant to do this . Just keep the plants clean of old decaying leaves , so you don't get any rot on your nice buds .
I had a friend who had a perfect grow but let everything get old leaf wise , die, then mold set into the leaves , then his buds before he finally harvested and lost most of his crop.
I didn't say anything to him about the way he grew until later, as it was none of my business , until he asked me to help save his crop . Then I told him what the problem was , but it was to late for most of his crop . He told me next time to tell him but I make a point of NOT telling people how to grow, only sharing what I've learned from my own mistakes . He's not good at listening to others . Now he listens but it's to late for that grow .
Get rid of the old leaves would be my adivce . Looking great !
From what I see with our weather , we'll have a early winter , but our weather can't seem to make up it's mind :) So you never know , but the plant above is finsihing out nicely and you can always keep your eye on the weather and wait as long as you can before you harvest . You'll know when that is in your area . Can't wait to see your harvested buds :)