You might have to do something. TurboTax Online for 2016 will not be available after October 16, in spite of the extended deadlines for disaster areas. You will have to use the CD or download TurboTax software to complete your 2016 tax return after that date. If you have started your 2016 tax return in TurboTax Online, you need to download the .tax2016 file now, so that you will be able to continue working on it with the CD/download software, and not have to start over.
If you have not started your 2016 tax return, but you used TurboTax Online for your 2015 tax return, you should download the .tax2015 file so that you can use it to transfer information from 2015 when you start your 2016 tax return. You should also download the PDF of your 2015 tax return so that you can refer to it after TurboTax Online shuts down.
After October 16 you will not be able to download anything from TurboTax Online until sometime in December.
If you are already using the CD/download TurboTax software, or if you have not started your 2016 tax return, and you did not use TurboTax Online for 2015, you don't have to do anything right now.
In any case, you will not be able to e-file your 2016 tax return. You will have to print it and file it by mail.
The IRS will automatically give you the extension based on your address.
However, this only applies if you had an approved extension to October 15, 2017. If you don't have an approved extension already your taxes were due April 15 and this does not change that.
Also note, your payment was still due April 15 even if you have an extension to file, so Harvey does not change any penalties you will owe for late payment.
And as explained in the other answer, you won't be able to use Turbotax Online after October 20.