"Today is pretty."
Translation:Nani kēia lā.
From the dictionary: Uʻi: "nvs[used as noun and as stative verb] Youthful, youthfully stalwart, heroic, handsome, pretty, beautiful, vigorous; youthful vigor and beauty, youthful hero..." Nani: "1. nvs beauty, glory, splendor; beautiful, pretty, glorious, splendid..." Uʻi seems better for describing a human, nani for describing other things. You wouldnʻt use uʻi to describe the weather. I welcome any clarifications from someone more knowledgeable than me.