Tromsø has rain forecast for each of the next three days: 3.5 mm today, 3 mm tomorrow and just over 6 mm on Thursday. Highs stay between 11 and 13 °C, which is mild for the Arctic in late September. Mild does not mean dry. On the fjord-side trails this steady drizzle works through a softshell within the hour. Take a waterproof shell and keep a dry layer in the pack for the way down.
Rain jackets ↗