Thursday will be a hot and humid day with a chance of thunderstorms in the afternoon and evening.

With high levels of ozone expected today, the National Weather Service has issued an Air Quality Alert for southern Fairfield, New Haven, Middlesex and New London counties from 11 a.m. to 11 p.m.

High ozone levels can increase the likelihood of respiratory symptoms and breathing discomfort in active children and adults with respiratory disease, such as asthma. The highest levels of ozone are expected in Greenwich, Westport, Stratford, New Haven, Madison and Groton. For the lastest ozone readings, click here.

Thursday’s high temperature will be in the upper 80s.

On Friday and the weekend, high temperatures will be about 10 degrees cooler.

Dry, cooler and less humid air will be ushered in for the weekend,with temperatures several degrees below normal.

The forecast

Today: A 40 percent chance of showers and thunderstorms, mainly after 2 p.m. Mostly sunny, with a high near 88. West wind 5 to 7 mph.

Tonight: Scattered showers and thunderstorms. Mostly cloudy, with a low around 65. West wind around 6 mph becoming north after midnight. Chance of precipitation is 50 perce

Friday: A 20 percent chance of showers before 10 a.m. Partly sunny, with a high near 79. Northwest wind around 6 mph.

Friday Night: Partly cloudy, with a low around 57. North wind 5 to 7 mph.

Saturday: Mostly sunny, with a high near 75. North wind 5 to 8 mph.

Saturday Night: Partly cloudy, with a low around 59.

Sunday: A 30 percent chance of showers after 1 p.m. Mostly sunny, with a high near 73.

Sunday Night: Mostly cloudy, with a low around 57.