Seattle broke the record for July 1, hitting 89 degrees. The previous record had stood at 87, set in 1995.
"That is not exceptionally hot, given the range of temperatures we see in the summer, but it's how early it is in the summer," said KING 5 Meteorologist Jeff Renner.
The temperature reached 93 in Winlock, 92 in Graham and 91 in Mercer Island.
An excessive heat warning was in effect until 11pm Monday for the central part of Puget Sound (Kitsap, King, Snohomish and Pierce counties), with a heat advisory covering the remainder of the interior of Western Washington.
Road sensor temperatures from the Department of Transportation recorded temperatures of 118 degrees on Interstate 5 at SR 524 and 115 degrees on I-5 at 144th.
Cooler ocean air will begin moving in on Tuesday, bringing cooler temperatures.
"Expect maximum temperatures in the upper 70s to mid 80s, warmest inland," said Renner.
The Fourth of July holiday will bring more morning clouds, then become partly to mostly sunny with highs in the mid to upper 70's. Very similar conditions are likely Friday.
The next 90 days, Western Washington is likely to have about average temperatures, said Renner.
"Eastern Washington, especially over the Rockies, likely warmer than average," he said.
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Snohomish County has a free life jacket program to help keep people safe on the water. There are closets set up at 10 county lakes and four fire departments with several life jackets for anyone to borrow for free.
"The main thing you want to make sure, is that they fit correctly," said Shawneri Guzman with Safe Kids Snohomish County. "All of the writing inside isn't just a tag. It has information."
Eight people have drowned in Snohomish County since January 1. But wearing a life jacket doesn't make you 100 percent safe in the water.
"These are not babysitters. Nothing replaces supervision," said Guzman.
Read more about how to make water safety a priority during hot weather.
Authorities also are advising people to protect themselves from heat-related illnesses and not to leave children or pets in cars. Pet safety information
Also, make sure that you have enough water for you as well as anyone with you. Staying hydrated will help you avoid heat stroke. CDC heat stress information