TheOldHippie is correct that some modern research tends toward a 3-syllable pronunciation for YHWH. The article written by George Wesley Buchanan, Professor Emeritus, Wesley Theological Seminary, in Biblical Archaeology Review, April 1995, comes to mind.
Many scholarly works also admit, as does the prestigious Anchor Bible Dictionary, that the pronunciation "Yahweh" is just a supposition, not a fact.
It is not true, as some suggest, that the Hebrew letters YHWH can be pronounced just any old way. Ancient Hebrew, like Modern Israeli Hebrew, was written without vowels, but certain combinations of letters had a standard way of being pronounced and understood. And for those who would deny that Modern Israeli Hebrew is NOT written without vowels, I suggest that you pull up the website of the Israeli newspaper Ha'aretz ( http://www.haaretz.co.il), which is printed in unvowelled Hebrew, which is easily read and understood by modern Jews.
The point is that when Hebrew was and is a living language, vowels are not needed to get at the correct pronunciation of words.
The medieval Hebrew scholar Maimonides in his Moreh Nevukim, or "Guide to the Perplexed," stated that anciently, the Divine Name was pronounced "as it was spelled." No vowels were necessary, since the letters H and W, as medial (not final) letters, would serve as "vowels" and would have to be pronounced in a certain way.
With that bit of wisdom, we come to a 3-syllable pronunciation for YHWH.
It is strange that those who would pronounce or interpret "Jesus" as coming from "Yehoshua" from the first part of the Divine Name, i.e., the YH-, have problems with Yehowah. If you accept "Yehoshua," then "Yehowah" is from the exact same pattern.
Also, the name "Jehovah" has nothing to do with "hovah" ("destruction"), since the two terms come from two completely different Hebrew roots. Those who make such a connection are arguing from an ignorance of the Hebrew language. The name "Jehovah" (Yehowah) is from "Hayah" (more anciently, "Hawah"), meaning "to be; to exist." The Hebrew Bible itself makes this connection at Exodus 3:14, 15.
It is further incorrect to say that the Name does not appear in New Testament, since Revelation 19 has Yah, the short form of YHWH, in the expression "Hallelu-Yah!"