Long Island forecast: Chantal's remnants could bring tropical downpours this week

Long Islanders should brace for persistent rainfall this week as the remnants of Tropical Storm Chantal move up the East Coast and bring the potential of flooding, forecasters said Sunday.

The storm system, which was moving over the Carolinas on Sunday, is expected to weaken as it churns toward the mid-Atlantic but will "converge together" with another front and bring moisture to Long Island, according to Newsday meteorologist Rich Von Ohlen.

"When they bump together, there will be opportunities for those tropical-type showers," Von Ohlen said.

The National Weather Service forecasts thunderstorms and showers in Nassau and Suffolk counties after 2 p.m. Monday, followed by a chance of rain every day for the remainder of the week.

The high temperature Monday will be about 84 degrees, with the wind out of the south at 7 mph to 11 mph, according to the weather service. The average high for the date in Islip is 82 degrees.

Multiple storm systems will interact with "tropical humidity" during the week to create a wide window for rain, resulting in the type of downpours typically seen in Florida, Von Ohlen said.

"Unfortunately, [Sunday] was the last of the nice beach days here," said Dave Radell, a meteorologist with the National Weather Service. "Not everyone is going to see rain, but for those that do, it could be heavy."

Matthew Wunsch, a meteorologist in the National Weather Service’s Upton office, said Chantal won’t linger for long but that "waves of moisture" from a system moving in from the Northwest will combine with high heat throughout the week to "bring "a chance of showers and thunderstorms pretty much every day, particularly in the afternoons."

The weather service expects highs in the mid-to-high 80s through the start of the weekend, with lows hovering in the mid-to-low 70s.

There might be a brief lull in rainy weather on Wednesday, Wunsch said, but a new system moving in on Thursday will bring another round of precipitation.

The consistent rainfall raises the potential for localized flooding, Wunsch said.

"With the amount of moisture that's present this week, any thunderstorm or heavier shower can definitely produce torrential rain," he said, though he added widespread flooding is not currently expected.

"It’s not going to be great this week," Wunsch said.

Newsday’s Bahar Ostadan contributed to this story.

By Joseph Ostapiuk

joseph.ostapiuk@newsday.com@OstapiukJ