Parts of the eastern United States began sweltering through a forecast three-day heat wave on Tuesday with the mercury topping 100 F (38 C) in some areas and New York City electricity demand setting a new record.

The heat wave moved across the country from California, which suffered more than two weeks of triple-digit temperatures that killed at least 136 people and caused power failures.

Temperatures hit or hovered near 100 degrees Fahrenheit in New York, Philadelphia and Washington, with hotter weather forecast for Wednesday. Detroit, St. Louis and Chicago were sweating it out in equally stifling temperatures.

The National Weather Service issued excessive heat warnings and said the heat index -- how hot it feels when the humidity is combined with the air temperature -- was due to hit 115 F (46 C) in New York on Wednesday.

The National Weather Service said more than 50 temperature records had been set in the central and western United States in the past two weeks.

Meteorologists are analyzing data to determine if July 2006 has surpassed July 1936 to become the hottest on record.

New York City has opened hundreds of air-conditioned "cooling centers" and extended hours at public swimming pools, while urging the public not to open fire hydrants.

Electricity grid operators did not expect to have to impose rolling blackouts, aimed at preventing uncontrolled outages, due to any lack of generating capacity.

However, in some regions, power distribution cables could fail, like those that recently left 25,000 Con Edison customers in New York without power for up to a week.

ConEd said late on Tuesday it had set a new record for peak electricity usage, reaching 13,103 megawatts at 5 p.m., which topped the previous record of 13,059 MW set on July 27, 2005.

In 2003, the worst blackout in North American history left up to 50 million people in Ontario, Canada, and eight U.S. states in the dark.

Commonwealth Edison reported about 10,000 scattered outages on Tuesday across its Illinois territory, including 2,700 customers on the south side of Chicago, who lost power Monday when an underground cable failed, spokesman Tom Stevens said.

In El Paso, Texas, heavy rains temporarily broke the region's drought and turned streets into raging rivers that uprooted trees and carried away cars.

PHOTO CAPTION

Chicago Cubs fan shields himself from the sun in Chicako Saturday, July 29, 2006. (AP)

Reuters