Automatic 2-month Extension of time to file and pay-Working overseas

[Art]

Taxpayer, US citizen and CA resident is currently working in Africa from Jan-Jun of this year and wants to file an extension to file and pay his federal taxes. The instructions in Pub 54 state that to qualify you must be living outside of the US on the due date of your return so he would seem to qualify. He is expected to owe about $15,000 and does not meet any of the normal exceptions for avoiding underpayment penalties (paying amount equal to last years tax or 90% of current year)
Question: Because he qualifies for this special extension will the normal underpayment penalties and interest still apply? Even if he manages to pay the full $15,000 by June 15, 2019?

[TaxGuyBill]

Yes, the normal underpayment of estimated tax penalty (which is basically interest on what should have been paid) will still apply. Just a reminder, the IRS announced a special provision for this year that changes the "90% of current year" to "80%".

If the tax is not paid by April 15th, interest on the amount due starts to apply.