Weather resistant (not sealed, emphasis made here just to be clear.....they have seals, but may not be great for floods and such) lenses have WR in their name. 16-55mm, 50-140mm, and the 18-135mm are it for now.
I have heard others suggest that using the other lenses in "moist" condition with careful use should be OK, and there are plenty of 3rd parties that sell lens sleeves to protect your lens. I bought my X-T1 with the 18-135mm because I wanted a weather resistant set-up....period. I like shooting in the rain and the snow. In those situations, the last ounce of lens IQ is hardly important..... and frankly, when one understands the limitations of designing an 8x zoom lens, the 18-135mm is a stud.