Ugaritic, for example, is essentially an abjad but has syllabic letters for  These are the only times that vowels are indicated.
jˌuːɡɑːɹɹˈɪɾɪk, fɔːɹ ɛɡzˈæmpəl, ɪz ᵻsˈɛnʃəli ɐn ɐbdʒˈæd bˌʌt hɐz sɪlˈæbɪk lˈɛɾɚz fɔːɹ ðiːz ɑːɹ ðɪ ˈoʊnli tˈaɪmz ðæt vˈaʊəlz ɑːɹ ˈɪndᵻkˌeɪɾᵻd.