Stifling, humid and downright oppressive, sultry is an adjective that has everything to do with sweltering heat and a definite need for a tall glass of iced tea.
You know how movies about the Old South always show people wilting in the shade of their front porches, mopping their damp brows? Well that's because of the sultry summer weather. A sultry atmosphere is a thick, almost swampy feeling. And all that heavy heat can certainly get passions stirring — "a sultry look" is one that happens to express steamy desire.