Then no, I mean...they are going to stop you don't you think? Even a perfect stranger would stop you if you warned them you are going to take your life.
The only thing I can think of is a way to send them a message after you are in the location you want to be and tell them it's getting ready to happen
I had to listen to a guy blow his brains out on a voicemail message to his girlfriend...25 years ago and I remember it clear as day.
You said that your dad is going to have a hard time. If you are set on self deliverance regardless of what your parents feel, you shouldn't warn them, chances are they will find a way to stop you.
I mean no disrespectful, but I'm guessing your fairly young? I spent most of my life trying to make my family care that I've been suicidal for most of my life. Did two stints in the hospital. They never changed, never acted like they give a shit, until I moved away last year and have just recently contacted them and begged for some help... no help, told I was sick and needed medication. So I warned them and it makes no difference.
You really need to evaluate your relationships and try to imagine what it might be like for them.
I know that sucks when no one cares about your pain and what you need, but maybe they really have no idea how badly your hurting, sometimes, we as parents...forget our children need something only we can give them.
I say, give them a chance to react to your warning, and you'll know how to move forward.