It's possible the temperature will hit 90 on June 18,...

It's possible the temperature will hit 90 on June 18, 2014, and many, like this lifeguard on July 18, 2013, at Dix Hills Park Swimming Pool, will need sunscreen and cooling. Credit: Jeffrey Basinger

It's another scorcher.

By midafternoon on the fifth day of a heat wave, it felt like 105 degrees Thursday at Long Island MacArthur Airport in Ronkonkoma, forecasters said. It was so hot that some commuters on their way home had to deal with roads buckling.

The heat advisory expired 8 p.m., with another issued for Friday from 11 a.m. to 8 p.m., according to the National Weather Service. A heat advisory is issued when the heat index -- which shows how hot it really feels, given the humidity level -- is expected to reach 100 or higher for two consecutive hours.

Indeed, Thursday became the fifth consecutive day with temperatures at 90 degrees or above, as MacArthur recorded 90 just before 10 a.m., with a heat index of 99. The day's high temperature there was 95 degrees around 2 p.m., short of the record for the day, 98 set in 1999. Three consecutive days of 90 or higher is officially a heat wave, the Upton-based service said.

As of late afternoon Thursday, the state transportation department reported road buckling on Route 231 southbound between Overton and Smith streets in Deer Park, and on the Long Island Expressway eastbound at Exit 67 in Yaphank. Just before 6 p.m. crews were on the sceneat both sites, said Eileen Peters, Department of Transportation spokeswoman.

That brings to five the number of bucklings on state roads since July 1, which are expected occurrences, especially "when the temperature is over 90 degrees and we have had rain within the prior week," she said.

Separately on Thursday, LIPA said it enacted its consumer peak-load reduction program, called LIPA Edge. The program, which cuts peak-load use by remotely raising thermostats of 31,000 participating LIPA customers, can cut up to 50 megawatts from the load. It's designed to stabilize the system during high demand and to cut future costs by reducing LIPA's state requirement for capacity, which is based on the peak demand.

As of 4 p.m. Thursday, LIPA had hit a peak of 5,740 megawatts, a high for the week.

Just under 1,000 customers were without power at 4 p.m. More than 20,000 customers have been affected by outages this week.

"LIPA has a sufficient supply to meet customer demand; however, these additional steps will reduce stress on the electrical system and can limit the amount of heat-related outages and restoration should they occur," John McMahon, LIPA's chief operating officer, said in a prepared statement.

Long Island also is under an air quality alert until 11 p.m. Thursday, with another issued for Friday from 11 a.m. to midnight, as determined by the state Department of Environmental Conservation.

The Long Island Water Conference urged residents Thursday to conserve water at this time, especially during peak morning hours, to improve water pressure and guarantee a sufficient supply for firefighter use. Don't scrimp, though, on drinking tap water to stay hydrated, the conference said in a news release.

As for Friday, temperatures are expected to be in the low- to mid-90s, with northwestern Nassau seeing the higher end of the range and the East End the lower, said Joey Picca, weather service meteorologist based in Upton. Heat indexes are expected to reach 102, the weather service said, but, "it's not out of the question" to see a site or two hit 105 degrees, Picca said.

The airport could see 90 degrees yet again Saturday, though that's not "a slam dunk," like Thursday's and Friday's forecasts, Morrin said. That's due to uncertainty over how fast the heat will be beaten down with the arrival of increasing clouds with showers and thunderstorms expected to develop late in the day, he said. There's also a slight risk for severe thunderstorms with heavy rain and gusty winds, the weather service said.

And, while people may think the shoreline has been mobbed, there have been "no overwhelming crowds" at state park beaches, said George Gorman, Long Island deputy regional director for state parks. Attendance has been steady and at levels expected, he said, but in such "oppressive heat" many people stay at home in air-conditioning and backyard pools.

The state Health Department advised limiting strenuous outdoor activity, particularly those most sensitive, the very young and those with respiratory problems, such as asthma and heart disease.

And while heat exhaustion and dehydration don't seem to be bringing people to his hospital, more indirect heat-related issues are, said Dr. Alan Kaplan, director of emergency medicine at Plainview Hospital. He said there has been an uptick in people coming in for treatment with underlying conditions such as diabetes and asthma, which are aggravated by heat.

With Mark Harrington, Nicholas Spangler and Gary Dymski

An earlier version of this story has an incorrect number of peak megawatts reported by LIPA. As of 4 p.m. Thursday, LIPA had hit a peak of 5,740 megawatts, a high for the week.

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