Some more information on the Ugaritic yw I was able to collect today in the library of the Collège de France Institute for Semitic Studies.
1. "yw" occurs only once in the Ugaritic texts, in the very lacunary text KTU 1.1 iv:14, as part of the "Baal and the sea (ym)" myth. As translated by G. Del Olmo Lete (Madrid, Cristiandad, 1981) the text MAY mean: "And the Benevolent, Ilu, the [Gracious] answered: [I will proclaim] the name of my son Yawu. The goddess [?] [his name is Beloved of Ilu]. And he called the name of Yammu (the Sea)." (N.B. What appears between brackets is just a guess for missing words.)
2. Some think in this instance the name "yw" is a scribal error, and they emend it variously (to "ym" or to "yr" for example). Or they interpret it diversely: as a variant name for Ym, as a noun meaning, for example, "beloved" (Gray), as an interjection "oh!" (Cassuto), as a verb "let there be" (Jirku). Most contemporary scholars, however, seem to accept it as a divine name, but they doubt whether or how it may correspond with Yhwh.
3. An "optimistic" interpretation can be found in N. Wyatt's Religious Texts from Ugarit (Sheffield Academic Press, 1998, p. 48): "This is probably a [Sanskrit] loan-word (<yau<dyaus) occurring in various [Near Eastern] contexts, including, perhaps, the [Divine Name] Yahweh. The apparent sense was 'lord', or even 'god', given the equation in BM 93035 ilu = yau."
4. A "pessimistic" interpretation is this of the long article Yahweh in the Dictionary of Deities and Demons in the Bible (DDD), ed. K. Van der Toorn (Leyden, Brill, 1995), col. 1713: "Yahweh was not known in Ugarit either [the previous negative reference is Ebla]; the singular name yw (vocalisation unknown) in a damaged passage of the Baal Cycle (KTU 1.1 iv:14) cannot convincingly be interpreted as an abbreviation for Yahweh."