Asian tiger mosquito. The story I heard is that it hitchhiked from Asia on a ship carrying old tires that landed in Florida, and has been moving northward ever since.
It was well established in North Carolina when I lived there, and has been in the Princeton area for a number of years. Note the striped abdomen, and you're likely to note also, much to your chagrin, that the tiger mosquito is very active during the day. Native mosquitoes tend to become active only at dusk.