If YHWH pronounced Yahweh is like the hiphil imperfect of the root HWH
(where the final H is a mater for an original Y rather than the real
voiced H found in roots like GBH "be high"), then what would the
shortened jussive form of this be? I think it would be YFHW. (yahu).
(YAH:WEH is shortened to YAH:W: as regularly with final H verbs; but
then as usual these forms become disyllabic by analogy with segolate
nouns, so YAH:W: becomes YFHW. with stress on first syllable by analogy
with &FXW. (saHu) "swimming" for &AX:W:)
This helps in explaining why Yahweh becomes -yahu with penultimate
stress when used as a suffix and therefore shortened.