Oh I'm sorry I misunderstood what you were asking for,
If you want it to sound like what you want, then I would suggest
(Tiernin) I guess you would change the sound of it and it the name would perhaps keep to its meaning, "Lordly".
The fada over the (á) sounds like; (aw) as in the english word "caw, and the (a) "...depending on the the neighboring consonants, either as in English tap or in English top, but with the lips unrounded..."(Ó Sé & Sheils, 2003, p. xi)
Ó Sé, D. and Sheils, J.(2003). Teach Yourself Irish. Hodder Education(1993) & Contemporary Books, a division of McGraw-Hill Companies(1994)