Have that air-conditioner ready for the weekend?

A looming heat wave that could last at least five days will bring the hottest temperatures of 2008 for the Philadelphia region and could even threaten records.

And it's not just the heat, it's the humidity, too.

Today and tomorrow, the high will be around 80, but then the heat will hit.

Saturday's predicted high is 97, just a degree shy of the 98 set during the historic heat wave of 1925.

That year, in a span of six days, the temperature hit 100 twice and 98 three times - setting records that still stand.

Sunday could also challege the record 95 set in 1999.

Monday calls for mid-90s heat, followed by highs in the low 90s for Tuesday and Wednesday.

Humidity will be a problem, too, with dew points expected to be at or above 65 - the number to remember for major mugginess.

The heat index - another measure of discomfort - "will easily make it into the upper 90s and possibly even reach 100 degrees ... or higher, making it uncomfortable for anyone to be outdoors," the National Weather Service warns about Saturday and Sunday.

Even the overnight lows are expected to be in the 70s from Saturday through Wednesday.

The heat will be a major departure from recent weather.

No day in May has even hit 85 yet, as measured at Philadelphia International Airport.

The warmest temperature so far this year was the 87 reached April 19.

For more forecast information, go to http://go.philly.com/weather.

Contact staff writer Peter Mucha at 215-854-4342 or pmucha@phillynews.com.