Long Island weather: Hot and humid, thunderstorms possible; Advisory for North Shore beaches

Long Island faces isolated showers and potential thunderstorms on Wednesday as humid conditions cause heat index values to rise into the upper 90s, the National Weather Service said.

Service meteorologist Bryan Ramsey said rain would be spotty and isolated Wednesday as compared to Tuesday's broader rainfall. The chance of precipitation should begin early Wednesday afternoon and last into Thursday morning.

"We are expecting some heavier downpours and maybe isolated spots of some of the stronger thunderstorms," Ramsey said. "So there's still going to be a marginal risk for some of the heavy downpours and flash flooding."

Most of the storm activity can be expected in the evening and overnight, primarily after 8 p.m., but the chances of precipitation increase after 2 a.m. according to the National Weather Service.

Moisture left behind from Tropical Storm Chantal is contributing to the thunderstorms, though the tropical storm is no longer a concern for Long Island.

The rest of the week will see highs in the 80s and a warmup over the weekend, with the chance of thunderstorms roughly each afternoon, the weather service said.

Due to heavy rainfall, Nassau County health officials closed 14 beaches to bathing as a precautionary measure, as they are prone to stormwater runoff.

The beaches include: Centre Island Sound, Ransom Beach, Soundside Beach and Stehli Beach in Bayville; Creek Club and Lattingtown Beach in Lattingtown; Laurel Hollow Beach in Laurel Hollow; Morgan Sound and Pryibil Beach in Glen Cove; North Hempstead Beach Park in Port Washington; Piping Rock Beach Club in Locust Valley; Theodore Roosevelt Beach in Oyster Bay; Sea Cliff Village Beach in Sea Cliff; and Tappen Beach in Glenwood Landing.

Similarly, Suffolk health officials issued an advisory against bathing at 28 beaches, including many on Long Island Sound and others at Cold Spring Harbor, Huntington Harbor and Bay, Centerport Harbor, Northport Harbor and Bay, and Smithtown.

The advisory is based on the potential that levels of bacteria at these beaches exceed New York State standards. Stormwater runoff can impact bathing water quality by elevating bacteria levels, which may cause exceedances of the New York State standard for bathing water quality, health officials said.

Beachgoers should also take caution over the weekend, as there will be moderate to high chances of rip currents.

Ramsey said Long Island continues to be in a rain deficit.

The service recorded 1.88 inches of rainfall at MacArthur Airport in June when the average amount should be 4 inches.

During Wednesday’s storms, Nassau County received about ¼ inch of rain. Although there were isolated reports in Suffolk of ½ to 1 inch of rain, the county generally received less than a quarter inch.

Not including Tuesday, Long Island has received 19.06 inches of rainfall since Jan 1.

"Yesterday aside, we are slightly below average, but not significantly," Ramsey said.

Newsday's Aidan Johnson contributed to this story.