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Weather service: MacArthur 24-hour rainfall record now official

A powerful rainstorm hit Long Island on Aug.

A powerful rainstorm hit Long Island on Aug. 13, dumping more than 13 inches of rain on MacArthur Airport -- which broke the New York State record for rainfall in a 24-hour period -- flooding roads and disrupting travel. Read More | Watch Video Credit: Ed Betz

It's official!

The 13.57 inches of rain that fell Aug. 12 to 13 at Long Island MacArthur Airport broke the previous New York State record for 24-hour rainfall, the National Weather Service said Wednesday.

Preliminary reports had pointed to that record. But after a team from the National Oceanic and Atmospheric Administration reviewed and verified data, including timing and the proper functioning of the rain gauge at the airport, it was deemed official, said Lauren Nash, a weather service meteorologist based in Upton.

Dropping to second place was the 11.6 inches that fell Aug. 27 to 28 in upstate Tannersville during 2011's Tropical Storm Irene.

A minute-by-minute look shows that 1.08 inches of rain fell Aug. 13 at MacArthur between 5:39 and 5:47 a.m., the weather service said on its website. By 5:54 a.m., 1.76 inches had been recorded.

The weather service also outlined the conditions that led to the historic rainfall and flash flooding that ensued. At play, Nash said, was "moisture streaming from the South" combining with a low-pressure system dropping heavy rain over central Long Island, all moving very slowly.

August's monthly rainfall figure for the airport -- where the weather service has kept records for the past 30 years -- was a stunner, with a total of 14.07 inches for the month, 10.09 inches above the norm.

That made it the airport's wettest August on record, the Northeast Regional Climate Center said on its site -- and 354 percent of the normal.

Last month's total rainfall also tied with that of October 2005 for the wettest month on record for MacArthur, said Samantha G. Borisoff, climatologist with the center at Cornell University. In that case, rainfall was spread out over the month, including major contributions from the remnants of a tropical storm and a nor'easter that drew moisture from Hurricane Wilma, she said.

Learn more about last month's historic rainfall at nwsdy.li/august2014flooding.

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