Landlord/Tenant Book Index - California Department of Consumer Affairs
You must give the landlord the same amount of notice as there are days between rent payments.193 This means that if you pay rent monthly, you must give the landlord written notice at least 30 days before you move.
Theres no way you'll get around paying September because of the short notice and your not positive of the date for settlement. However, should you decide to give only two weeks notice and if the LL rents the unit out during that month, they have to prorate and refund for the days after the new tenant signed the lease. Rent can not be collected on the same unit twice.
Why can't you give your 30 day notice now to begin September 1st, so your security deposit will be refunded.
The rents paid for the month, but you can leave anytime during the month.
Theres also the possibility you can negotiate if the LL is willing to begin your termination notice the day after receipt, so if you did this now, that would take you to the middle of September. The refund of the security deposit will make up for the loss in rent and if the unit is rented out anytime after your move out, if the LL hasn't prorated your rent for that month (he doesn't have to) he owes you a refund for the days after the new tenant signs their lease. Just throwing out suggestions.