Heat wave sets in on West Coast with worst yet to come

Heat alerts have been issued for 26 states from Washington to Florida on Thursday, with more than 120 million on alert for sweltering temperatures -- especially on the West Coast.

The dangerous heat has already claimed the life of a 10-year-old boy who was hiking in Phoenix on Tuesday.

The prolonged heat could be one for the record books, and one of the worst heat waves in 18 years for parts of California.

Several wildfires also exploded in the West due to dry conditions and ongoing heat.

Among the worst of those fires is the Thompson Fire in Butte County, California, north of Sacramento, which has grown to over 3,500 acres with 7% containment.

Some 28,000 people had been evacuated due to the fire, with evacuation orders still in place Thursday for parts of Butte County.

More than 12,000 structures are threatened, and four have been destroyed, amid the fire, officials said Thursday.

Temperatures in the region are expected to be as high as 110 degrees Thursday, which "increases the chances for fire growth," Cal Fire said .

Heat alerts have been issued for Los Angeles, San Francisco, Seattle and Portland, Oregon. It is not common to get high heat this close to the coast and this far north.

Dozens of record highs are expected over the next week in the West. On Thursday, we could see daily records fall in San Angelo, Texas (projected: 104, record: 105); San Francisco (projected: 86, record: 85); and Medford, Oregon (projected: 106; record: 103).

Across the South, the heat will be combined with high humidity to make it feel like 110 to 115 degrees.

A heat advisory was also issued for Philadelphia and Washington, D.C., where the heat index could reach 100 to 107 degrees Thursday and Friday.