Although Yahwah is a close variation, the mistake is establishing a pronunciation by using Strong’s 1933 as well as 1961, although 1933 is related in meaning (existence) it is however a different word. The Hebrew of 1961, hay-yod-hay, is not the same as the 1933 cognate, hay-wa-hay. The first is pronounced hayah, the second hawah. The error is in fusing these two different words to make Yahwah without any linguistic basis or evidence to do so.
Another argument for the “ah” ending is that if the sound of the first hay is “ah,” the second hay must be the same sound. The same letter often takes on a different sound when appearing twice in the same word. For example, the “a” in always is not the same sound at the beginning of the word as it is at the end. Just because words are related in their roots is no justification for manufacturing a word or name by combining variations and should be disregarded as poor scholarship. The Berlitz Hebrew Self-Teacher on page 73 reveals: “There are, however, four letters which can be used as vowels. h and a may have the vowel sound of ah or eh, w that of oo or oh, and y of ee or eh.”
The Greek shows that the last syllable is pronounced with a short “e” sound: ee-ah-oo-eh. The name Yahweh is shown on various Greek transcriptions, such as ιαβε, dating from the first centuries CE.