It will be fine, the key with pressure washing is to keep the nozzle as far away from the surface as you can, although with an 1800 PSI pressure washer you will have a hard time damaging wood unless you put the nozzle right on the surface, or use the narrow angle jet-type nozzle which don't have much for anything except extremely durable materials like steel. If you have never used a pressure washer I would recommend testing out the various nozzles and distances on a piece of scrap wood so you can get a good idea of how easily it might damage something.

Honestly, I live in the northeast where it gets extremely humid and I've been pressure washing yearly for two decades, I can't say I've ever permanently damaged anything, but you obviously want to be careful with anything that's painted (although a proper exterior paint, applied correctly, should be able to be pressure washed without stripping it) or finer decorative materials.

Also, my personal suggestion for an electric pressure washer having been through many crappy ones is anything by AR Blue, inexpensive but the parts that matter are good. The one I have now ended up running for multiple hours overnight while dry (a lesson to never leave them plugged in...) and it was so hot I thought for sure the pump would have failed, and was surprised the thing didn't short circuit or catch fire, but it's been years and I am still using it with no problems.