storm damage
© Christian Snyder/Post-Gazette
A late-night storm poured 3.38 inches of rain on northern Allegheny County plus the southern portions of Armstrong, Beaver and Butler counties, shattering a 107-year-old record and making Sunday the Pittsburgh region's wettest Sept. 1.

Jared Rackley, a meteorologist with the National Weather Service in Moon, said it was the wettest Sept. 1 since 1871, the year the organization began keeping records of the Pittsburgh region's weather.

Measured at Pittsburgh International Airport, the 3.38 inches of rain was more than double the 1.29 inches that fell on Sept. 1, 1912, said Shannon Hefferan, also a meteorologist and one of Mr. Rackley's colleagues.

There was no direct link between Sunday's heavy rainfall and Hurricane Dorian, which was pounding the Bahamas, Mr. Rackley said.

Sunday's storm also increased the Pittsburgh region's precipitation for 2019 to 38.21 inches, topping the average of 38.19 inches in precipitation thanks to a combination of rain and snow melt, according to Ms. Hefferan.

The rain should clear out and make way for sunny weather on Tuesday, with a 40% chance of rain on Wednesday, according to the Weather Service.

At this time of year, said Myranda Fullerton, another Weather Service meteorologist, the average temperature is 79 degrees, but on Tuesday the high will be 82. A cold front that arrives Wednesday will lower temperatures to the mid-70s.

Dorian, a tropical storm that became a Category 5 hurricane, spent the weekend hovering over the Bahamas. Downgraded to a Category 4, it is expected to parallel the East Coast.

As Dorian turns northeast, AccuWeather said, people from Georgia to North Carolina, who are under orders to evacuate, should prepare for damaging winds, torrential rains and pounding waves.

"Even though Dorian is forecast to gradually lose intensity near the eye, the hurricane will gradually grow in girth in the coming days," said Dan Kottlowski, an AccuWeather hurricane expert.

"This means that the areal extent of hurricane and tropical storm conditions will increase as Dorian encounters the United States," Mr. Kottlowski said. "People can expect a storm surge of 4-7 feet with locally higher inundation from east-central Florida to southeastern Virginia associated with Dorian."

A waterspout or tornado can occur anywhere in a hurricane's spiral bands but the greatest risk will be in the northeastern quadrant of the storm as it nears the coast in North Carolina, according to AccuWeather.

Four times a day, the National Weather Service in Moon is launching balloons measuring a couple of feet in diameter to gather weather data, Ms. Fullerton said.

"We launch an instrument that tracks the temperature, relative humidity and the wind. We get a read of the atmosphere as the balloon goes up," she said.

"As the pressure decreases the balloon gets bigger and bigger until it eventually pops. The raw data that the balloon collects, Ms. Fullerton said, "can be fed into the models to get a better handle on storms like Dorian."

Normally, these balloons are launched twice a day but with Dorian, Ms. Fullerton said, "We are doing it four times a day."