Some articles on sapostu:

Modal Verbs in Other Languages - Hawaiian Creole English
... "have got to", haeftu "have to", baeta "had better", sapostu "am/is/are supposed to" ... can indicate past tense before the future/volitional marker gon and the modal sapostu Ai waz gon lift weits "I was gonna lift weights" Ai waz sapostu go "I was supposed to go" ...