My DD was born in November and we're in Brisbane - but she was still fine in a capsule.

Our car is airconned, has dark tinted windows and we also used those stick on sun shade thingos. Also she was really only put in it just before we left the house, and straight out again when we got home and in the car in between.
This bub will be summer again and we're using a capsule as well. It gets up to mid-high 30's here in summer with killer humidity, so I think you'll be fine