Wednesday is a flip-flop and tropical-shirt summer-kind-of-day across Long Island, the National Weather Service said.

Daily highs reached from the low to upper 80s across Nassau and Suffolk counties, with light winds starting from the west then shifting southwest from 9 to 14 mph.

By 11 a.m. it was already 80 degrees at Long Island MacArthur Airport, making it the warmest day of the year so far.

News 12 Long Island meteorologist Rich Hoffman said Wednesday starts a stretch of warm days that include above-normal temperatures into the weekend.

He said temps in western Nassau could be a bit warmer Wednesday, while it could be markedly cooler — in the 70s — at the beaches.

The service’s Upton office said the state Department of Environmental Conservation has issued an air quality alert for Long Island, in effect until 11 p.m. Wednesday. The alert is also effective from 11 a.m. to 11 p.m. Thursday.

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The alert means outdoor air quality levels can have adverse health effects for those with respiratory issues, including asthma. The alerts are triggered when the Air Quality Index is above 100.

Hoffman also said to expect a high ultraviolet radiation index, so have the sunscreen handy.

Skies continue to be clear overnight and into Thursday morning, Hoffman said. Some fog may develop but should give way to clear morning conditions. Overnight lows are expected in the 60s.

Thursday also is mostly sunny and warm, with highs near 83 degrees.

Again, western Nassau could get slightly warmer temperatures with the South Shore a bit cooler, Hoffman said.

Friday and Saturday also look to be mostly sunny, but the extended Memorial Day weekend could see morning showers on Sunday and Monday, Hoffman said.