Power supplies in the city and its suburbs on Long Island and Connecticut are some of the tightest in the nation because construction of new power plants and transmission lines has not kept pace with the region's economic and population growth.

This week, LIPA, which serves more than 1.1 million customers on Long Island, expects to have enough power available to meet the peak load of near 4,600 megawatts. On Tuesday, LIPA had about 5,400 MW of supply.

One megawatt is enough energy to power about 1,000 homes.

For the most part, the utilities serving nearly 60 million people from Maine to Virginia have enough energy to meet the demand for electricity on hot summer days when air conditioners consume about a third of all the power generated.

But, as officials at New York City's utility, Consolidated Edison Inc. , have said, the loss of a major transmission line or power plant during a heat wave could lead to short-term, localized brownouts or blackouts, especially when power supplies are tight.

Residents of metropolitan New York are expected to use the most energy this week and Thursday when meteorologists forecast temperatures would reach between 92 F and 96 F and the heat index, which combines the effect of the heat and humidity, will make it feel like more than 100 F degrees.

Despite the hot weather, the New York ISO, which operates the power grid for more than 19 million New Yorkers, does not expect any electricity demand records to be broken.

The record peak in New York is 30,963 MW set on Aug. 9, 2001, during a long heat wave.

Grid operators in New England and the Mid-Atlantic states also expect the hot, humid weather to push electric demand to near record levels this week, but not to set any new records.

Philadelphia, where the heat index has remained above 90 F all week, is expected to see high temperatures of 96 F this week and Thursday, according to AccuWeather.

It will be a little cooler in New England with Hartford, Connecticut, reaching a high of 91 F this week before slipping to a high under 90 F yesterday.

The hazy, hot and humid weather is expected to break Thursday afternoon as thunderstorms crash across the region, marking the approach of a cold front from Canada.