If the subtle brush of Obito's chakra hadn't alerted him, then the tapping most certainly did. Standing at the sink of his kitchenette in loose fatigues and robe, Yamato peered over his shoulder and reached for a nearby cloth to dry his hands.

"..Obito?"

In all honestly, by the knock, he'd expected Kakashi; Obito rarely offered the courtesy of announcing his presence and doing so now, ticked off several tick boxes in Yamato's head as to what type of visit it would be.
The cloth was dropped to the low table in front of his couch as he stepped closer to the window, nodding for the other man to come in and offering a warm smile.

"Come in and close the window, it's freezing out."