SOUTHERN CALIFORNIA - Well Los Angeles and Orange County are in such close proximity so they will have similar weather patterns. But Los Angeles gets hotter in the summer and more rain in the winter compared to San Diego. So Costal Orange County would be the best in the local area, Inland Orange County gets much hotter compared to the coastal portion.
BAJA CALIFORNIA - Tijuana is just south of San Diego in the Mexican state of Baja California. They share similar weather patterns. 70 miles south is another major city, Ensenada. Ensenada has very nice weather too.
HONOLULU, HAWAII - I went to Maui, one of the Hawaiian islands, a couple years ago. This reminded me of the nice weather. On wikipedia, it says Honolulu's averages temperature is generally in the low 80's. And they actually have similar rain fall patterns through out the year.
ROME, ITALY - On woldclimate.com, it had top picks. I choose ROME and selected the LATINA area of ROME. IT has similar weather except it gets a little more hot in the summer and liltle cooler in the winter. So it doesn't hold a similar temperature all year round like San Diego but it is comparable.
The whole thing people are saying about thing on the same longitude doesn't work. Go 200 miles east of San Diego and your in burning desert. Go a little further and you in Phoenix, Arizona which is very hot. Go to the east coast and your in Southern Humid Weather. Weather along the coast is mainly effected by the ocean and wind from around the world.