Avoiding Penalty After A Roth Conversion Late In 2019

My wife has a Traditional IRA that we want to convert to a Roth IRA before the end of calendar year 2019. Obviously, we will not be able to submit quarterly income tax payments to the IRS for calendar year 2019 because there are only 2 quarterly payment dates remaining. Is there a way that we can avoid an Income Tax Penalty for our income tax for 2019 due to this Roth IRA Conversion? If we have 10% withheld for the conversion (like we do for our annual RMD), that will be an amount a little over our Total Tax Owed for 2018 (Safe Harbor Rule). Any suggestions on how to avoid a penalty for this Roth Conversion? Thank you.