Are you sure about that? Alabama doesn't allow you to reduce your state taxable income by the federal standard or itemized deduction you claim? Because if it does then those deductions are gone and you should see your state income taxes go up as well.
This is just the amount of State Tax withheld from my pay, I am not looking at state filing, deductions, etc. That amount will not change under 9-9-9. There may be some changes to my state taxes at filing time, but as I said this was just a simple up front analysis of the effect on my monthly income from a federal perspective.