Over 90 million Americans on alert due to extreme heat

On Wednesday, heat warnings were issued for 21 states from Washington to Florida, with more than 90 million people on alert for extreme weather conditions.

Due to the dry conditions and persistent heat, several forest fires also broke out in the west on Tuesday.

In the West, the dangerous heat has only just begun, but on Tuesday a 10-year-old boy was killed while hiking in Phoenix.

This sustained heat could go down in the record books and be one of the worst in 18 years for parts of California.

A heat warning has been issued for coastal cities such as Los Angeles and San Francisco. Temperatures there could rise to almost 32 degrees on Wednesday. Inland, temperatures could rise to as much as 43 degrees.

Dozens of record temperatures are expected in the West over the next week, even as far away as Seattle and Portland, Oregon.

In the South and the Mississippi Valley, the combination of heat and humidity could push the heat index above 43 degrees.