You always pack so you can dress in layers. The weather can get into the low 80's it can also be in the 50's. Ketchikan is a rain forest so count on rain. You may need everything from shorts to jackets depending on what you consider cold. Take some summer clothes and take some warm clothes. The weather can also change quickly in Alaska.
Just left Ketchikan on May 7th. for 1 week I wore jeans/t-shirt/denim shirt as a jacket - from 5 a.m. being outdoors until after 9 in the evening.
I've spent 3 summers there - and have worn everything from ski wear in August to tank tops and shorts.
Just like the Boy Scouts-be prepared! A sweat shirt or Polar Fleece jacket covered by waterproof rain wear is sufficient. Sturdy walking shoes, preferably waterproof - are necessary. This year, people in Ketchikan are preparing for more warmth than is usual.