Jaffa is 4,000 years older than Tel Aviv and shows it. The streets are narrow, the buildings are stone, and the merchants long ago figured out that the only way to keep a flea market alive in August is to string awnings across the whole grid. From Yefet through the Pishpeshim and up to the clock tower, the awning canopy is more or less continuous.
These three pick the cool side of each lane. Avoid Yefet itself (wide, exposed) and stick to the parallel back streets — Bet Eshel and Olei Tzion get the awnings and the breeze off the port.