How does one translate the probable future tense? "He must have forgotten his appointments." or "He must have missed the plane." or "James must already be in London."

Speculating about a past probability /possibility?
Use that auxiliary verb + perfect tense

1. He must have forgotten his appointments.
     Li dwe te bliye randevou li yo.

2. He must have missed his flight.
     Li dwe te manke vòl la.

3. James must be in London by now.
    James dwe nan Lond kounye a.

4. The juice spilled because you must have not closed the bottle properly.
     Ji a koule paske ou dwe pa't byen  fèmen boutèy la.

5. She missed the concert because she must have been ill.
    Li pa't nan konsè a paske li dwe te malad.

Haitian Creole ↔ English Reference, Look up Haitian Creole and English Words