“While inclining to view the pronunciation "Yah.weh" as the more correct way, we have retained the form "Jehovah" because of people's familiarity with it since the 14th century.” (The Kingdom Interlinear Translation of the Greek Scriptures, 1969, p. 23).
Confirmation from Jewish scholarship:
“JEHOVAH is a mispronunciation of the Hebrew YHWH the name of God. This pronunciation is grammatically impossible. The form ‘Jehovah’ is a philological impossibility.” (The Jewish Encyclopedia)