The letters Waw و and Yaa ي are also called Leen letters because they are flexible letters. They blend with the vowel sound from the previous letter, allowing two vowel sounds.
waw leen Soft was
When a letter having Fat’hah is followed by letter Waw the vowel sound starts off as an ‘a’ sound and ends as a ‘u’ sound (rhymes with Cow). it produces "ow" sound ("au" some cases). This is called waw Leen or “soft waw”