We are planning a trip to Seattle in late September/ early October. Is this time too late to visit Olympic?
After May early October is my favorite time in Olympic for many reasons. The only thing that you need to consider is that the further into that time that you get the better chance of rain especially on the the Westside. Does that mean that rain and not sunshine is a sure thing? Absolutely not. Just no way to predict. Keep in mind that access to the Hoh Rainforest may not be possible until sometime in mid October due to much needed road repair. The Quinault Rainforest should be added to your itinerary. It is also glorious that time of year.
It's a lovely time of year, except, perhaps, for the last week of October, a transition period. It is also a lot less crowded, and road construction tends to be over by October.
I am not going to guess on when the road construction will be completed. Could be, but it is a difficult project so I do not see where anyone can predict that it will be completed on schedule before they even start.
The construction is supposed to last 5 months, and it started in early May. It's a huge project, however, and the county made no attempt whatsoever to mitigate the effects on visitors to Hurricane Ridge, the most popular site in the park. As a resident of Clallam County and Port Angeles, I almost feel that the county went out of its way to stick it to the park visitors. That would be shortsighted and plain dumb, given the economic value of the park to the region, but it fits in with the backward attitudes of some of the people here. A few of them thought, and probably still think, that the World Heritage Designation of the Hoh Rain Forest was a UN plot to take over the Olympic Peninsula.
This is totally different from the big construction project along Lake Crescent. Not only is this project literally a lifesaver, but the project management has done everything possible to ease the burden on visitors and residents who need to use the road.