"How is the afternoon Rehema?"
Translation:Habari za mchana Rehema?
They both essentially mean the same thing. Za and ya are both prepositions meaning of.
Habari za/ya asubuhi is literally translates into "What news of the morning?" but means "How is the morning".
A dictionary states:
-a is the invariable element, which combined with a prefix forms the various prepositions wa, ya, za, cha, la, pa, kwa, ??iwa. In meaning these all correspond generally to the English 'of,' and (with the noun following) to the Genitive Case in the classical languages, and include all such adjec- tival relations as ' belonging to, pro- ceeding from, consisting of, of the class or kind of, relating to, qualified by,'
Wikipedia says that ya is used with noun classes 4, 6, and 9. Za is used with noun class 10.
Yes, I probably do have some incorrect info. I am native English and I don't know much Swahili. I'd rather be partly wrong with confidence than correct with a lot of "I think" and "I may be wrong" and other unsure statements where the reader would probably ignore everything I say because they don't know if they can trust me.