Cities such as Vancouver (British Columbia), Seattle (Washington) and Portland (Oregon) get a lot of rain. “The wet coast” was cited in the book Canada: This Land of Ours (1976). The term was poplalrized by Tom Parkin in his book, Wet Coast Words: A Dictionary of British Columbia Words and Phrases (1989). “Wet Coast” almost always refers to British Columbia and seldom refers to Seattle or Portland, but an extension of the “wet coast” term could occur.
 
A similar “wet”-for-“west” nickname is “Northwet” (Pacific Northwest + wet).
 
 
Google Books
Canada:
This Land of Ours
By William H. Wiley; et al.
Toronto: Ginn
1976
Pg. 107:
The wet coast
The coast of British Columbia has abundant rainfall. In fact, some parts of it have too much.
   
OCLC WorldCat record
Wet coast words : a dictionary of British Columbia words and phrases
Author: Tom Parkin
Publisher: Victoria, B.C., Canada : Orca Book Publishers, ©1989.
Edition/Format:   Book : English
 
Google Books
Bush Basics:
A Common Sense Guide to Backwoods Adventure
By Glen Stedham
Victoria, BC; Custer, WA: Orca Book Publishers
1997
Pg. 15:
BAD WEATHER TIPS
Much of my hiking is done on the west coast of British Columbia, sometimes called the “wet coast,” with rain, high humidity, clouds, and limited sunshine.
   
Google Books
The Toddler’s Busy Book
By Trish Kuffner
Minnetonka, MN: Meadowbrook Press
1999
Pg. ?:
The west coast of British Columbia, where we live, is often called “the wet coast.”
 
5 September 2003, Rocky Mountain News (Denver, CO):
Associated Press
The city that critics like to call Raincouver, a.k.a. the Wet Coast, a.k.a. the umbrella capital of the universe—Vancouver, British Columbia—is suffering drought.
 
Google Books
The Penguin Book of Canadian Jokes
By John Robert Colombo
Toronto: Penguin
2001
Pg. 433:
It hardly ever rains in British Columbia. But when it does, they call it precipitation. Wags refer to the West Coast as “the Wet Coast.”
 
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Vancouver (Insight City Guide)
By Cathy Muscat, Discovery Channel (Firm)
Singapore: APA Publications (HK); Long Island City, NY: Distribution, Langenscheidt Publishers, Inc.
2007
Pg. 53:
British Columbia has been dubbed the “Wet Coast”.
 
Winnipeg (Manitoba) Free Press
THE VIEW FROM THE WEST
Come join the parties on Wet Coast
By: Marilyn Baker
Posted: 01/21/2011 1:00 AM
I have a moral dilemma. I want to join the Liberal party of B.C. before the cut-off for the leadership vote on Feb. 26. If I do, my membership gives me the right to vote on which of several candidates will become the leader of the party, and ergo, the premier of the province of British Columbia until 2013.