WA has no state income tax.  You say you are doing volunteer work--do you mean you are not being paid at all?  If you have no income in the state (what state?) you are volunteering in, then you do not need to file a state return there either.  Provide some more information--why are you worried about what state to say you live in?  If you just need to know what to put on your federal return for your address--use the address where you want to receive mail from the IRS.

Have you had any income during 2019?

DO I NEED TO FILE A TAX RETURN?

https://www.irs.gov/help/ita/do-i-need-to-file-a-tax-return

I am a church missionary and live in the State of Hawaii.  I pay for all my expenses here but I plan to return to my permanent home of record in Washington State.  I am just asking the question about how long I have lived in the State for the year of 2019.  I assume it is all year, since I don't plan to change my home of record and I rent here in Hawaii.  

Then you say you have lived in Hawaii for the year of 2019.  The question still--what income are you even entering on any tax return if you are a volunteer?  What are you trying to put on a tax return?