On a seperate note, you might want reconsider jeans. The heat, and especially the humidity, will make denim and heavyweight fabrics less than comfortable. I say this as someone who has spent a day no more than three feet from a toliet after insisting on wearing my "coolest" jeans to the neighborhood house tour (as much time indoors as out) and becoming overheated. If you are unaccustomed to what a difference high humidity makes at 90 degrees, please seriously look into travel websites and their clothing recommendations. D.C. was under a heat advisory just last week, and while we may luck out in July, I wouldn't count on it.  I doubt you want spend money on clothes shopping or cab rides because you are not prepared for the climate