Notice what The Jewish Encyclopedia of 1901, Volume 12, page 119, states.
It thus becomes possible to determine with a fair degree of certainty the historical pronunciation of the Tetragrammaton, the results agreeing with the statement of Ex. iii. 14, in which YHWH terms Himself hyha. "I will be", a phrase which is immediately proceeded by the fuller term "I will be that I will be," or, as in the English versions, "I am" and "I am that I am." The name hwhy is accordingly derived from the root hwh (=hyh), and is regarded as an imperfect. This passage is decisive for the pronunciation "Yahweh"; for the etymology was undoubtedly based on the known word.
The Encyclopedia Judaica, Volume 7, page 680, further states this fact.
The true pronunciation of the name YHWH was never lost. Several early Greek writers of the Christian Church testify that the name was pronounced "Yahweh". This is confirmed, at least for the vowel of the first syllable of the name, by the shorter form Yah, which is sometimes used in poetry (e.g., Ex. 15:2) and the -yahu or -yah that serves as the final syllable in very many Hebrew names.