The form Yahwoh is as much of an assumption as other proposed pronunciations.
The form Yahweh is how Latin would pronounce IOVE or the Roman name for Jupiter (Deus Pater, God Father). And btw the Latin form for Joshua/Jehoshua is IOSUE. (Notice the Hebrew ending AH changing to E in both).
The form Jehovah in some of our Bibles is an Anglicization of YHWH as is Judah/Jehudah for YHWDH. (Take off the D in there and what are you left with? YHWH Jehuah).