The temperature could even reach 27 C in some parts of the country, according to one model, but the warmth may be short-lived - just a day or two.
The National Weather Service said that summer this year will be more showery than previous years. Those who have planned their vacation in this week should consider themselves lucky - the upcoming week will be the warmest glimpse of summer for a long time, a forecaster said.
July started with a grey tone following the current temperature pattern of 9-18 C - with some places in 20-21 C - until Friday when the clouds clear and the temperature soars to 24 degrees Celsius.
Water temperatures will also start increasing after the second week of July when the sudden heat peak has had enough of an effect on the bay areas, forecasters say.