Storms that devastated northern Suffolk were intense, hard to predict, experts say

The system that pelted Long Island Sunday into Monday, devastating parts of Suffolk County, moved in with a fierce intensity, then, without much warning, slowed down and stalled.

Releasing bands of rain over several communities overnight, meteorologists said, it dumped more than 9 inches, causing catastrophic flooding on the North Shore.

"This storm was not predicted for Northern Suffolk," Suffolk County Executive Edward P. Romaine said Monday. "When you get almost 10 inches of rain, that’s a once in a 100-year storm. I don’t think we’re going to have to wait another 100 years. It tells you the impact climate change is having on our weather and the natural disasters we’re having."

Meteorologists said no single storm can be attributed to climate change, but experts noted such storms are becoming more frequent and are subject to periods of heavy rainfall that can cause widespread damage. They can also be hard to predict, experts say.

Kevin Reed, associate provost for climate and sustainability programming at Stony Brook University, said storms like the remnants of Hurricane Ida and Isaias that impacted Long Island in recent years show how weather has grown more volatile, with increased propensity for heavy rain.

He said it can be harder to predict heavy rainfall that can be localized, like in parts of Suffolk County.

"The likelihood of extreme rainfall during these events is increasing," Reed said. "With these types of extreme weather events on Long Island, we happen to be in an area that has a lot of extreme weather and where it occurs, it exemplifies it."

Long Island’s humid weather can sometimes recreate tropical conditions, Newsday meteorologist Rich Von Ohlen said.

"Summer weather patterns on Long Island can be very similar to Florida, with sudden heavy tropical rain bands that do not move much," Von Ohlen said. 

Forecasters said the storm caught many off guard before the warm tropical air stalled over Long Island, increasing in intensity over slightly elevated regions of Stony Brook and Rocky Point.

"The speed of the storm slowed down, and many times intense rain that doesn’t sweep through, steadily causes rain over the same area for a long time," Von Ohlen said. "The problem is the models that predict these patterns don’t get it perfectly right and a little bit of error in the rain bands can make a big difference."

The western front of the system entered a humid atmosphere Sunday with a strong lift that created heavy rain and camped over Connecticut and parts of Suffolk County, National Weather Service meteorologist James Tomasini said.

He said warmer temperatures can hold more moisture, creating heavy rain. He said the storm event would be reviewed by the weather service, but noted the forecast never usually predicts up to 10 inches of rain during one period.

"The storms are not able to move very fast and are favorable for rain," Tomasini said, explaining how these storms sometimes stall.

Predicting the smaller storms, with intense bands of rain, can be more difficult than larger storms or hurricanes, said Kristina Dahl, principal climate scientist at the Union of Concerned Scientists.

She said heavy and short-lived rainstorms, although not individually traced to climate change, are signs of a warming atmosphere. She said while storms have always existed, along with strengthening hurricanes, sudden storms with intense rain are becoming more frequent.

"Events like this are incredibly concerning. This is not the first such incident we’ve seen this year. They are consistent with the trends we’re seeing of climate change," Dahl said. "It is much harder to predict and forecast these storms that are stronger and not as long lasting."

By John Asbury

john.asbury@newsday.comJohnAsbury

John Asbury is a breaking news and general assignment reporter. He has been with Newsday since 2014 and previously worked at The Press-Enterprise in Riverside, California.