The sound of thunder and rain pelting the ground this summer is the sound of money –– swiftly going down the drain.

For the last six weeks, sun-dependent businesses –– house painters and roofers, beach shops and lemonade stands –– have been glumly waiting for the skies to clear, while watching their bottom lines suffer.

“I can’t believe there’s this much rain in the sky. And it’s all coming down on Rhode Island,” Joe Padula, the executive vice president of Del’s Lemonade, said as thunder rumbled outside the Cranston headquarters Friday afternoon. “What did we do wrong?”

Another half-inch of rain fell in localized showers throughout Rhode Island on Friday, adding to the deluge that came down Wednesday and Thursday. The trouble is a stagnant weather system that’s been hanging over Southern New England, with heavy rain further slowing its departure, said meteorologist Charlie Foley, at the National Weather Service.

The sun is expected to make an appearance Saturday morning, and may disappear briefly in afternoon showers before clear skies return for fireworks at night, Foley said.

Sunday will bring the first perfect summer day of 2009 –– sunny skies and 80-degree weather. That’s good news for lemonade stands, seaside businesses and roofers, but not enough for house painters, who need to wait for a stretch of good days for surfaces to dry out.

And, for seasonal businesses, a good day in early July doesn’t make up for six weeks of clouds and rain in May and June.

Padula estimated that the lemonade business was down 40 percent because of the rainy weather. “I’ve been in this business since I was 7 years old and picking up paper in the parking lot,” said the 61-year-old man. “This is the second worst beginning or middle [season] in my entire life.”

The worst, he said, was one summer years ago when it rained 14 out of 18 weekends in a season. This summer “has been tough for everybody,” Padula said. “I feel bad for the people who have vacations. You just get two weeks out of the year for your vacation, and it rains.”

The South County Tourism Council is working hard to be hopeful. When council president Myrna George is asked about the weather, she says, “When it rains, our museums really shine.”

But the beaches? George said she’s optimistic that people are delaying their vacations until the end of the season. “People are craving vacation time, with the gloom and prediction of the economy,” she said.

The weather “has most definitely affected us,” Jannette Centracchio, ticket office manager for the Block Island Ferry, said bluntly. “There’s no real scientific explanation. When the sun’s out, we’re busy. When it’s not, we’re not.”

It’s the same for roofing contractors and painters, who are watching their prime season wash away. They can prep, but they can’t paint. Roofers can buy the materials, but they can’t strip a roof in the rain. The weather delays projects in an already short season.

“It’s kind of crazy,” said Will Donnell, the president of CertaPro Painters of Northern Rhode Island. “We were concerned about the economy. But we were ahead in bookings, and now production is behind.”

Contractors say the rainy weather has added another burden to an already difficult climate. They’re dealing with the troubles that began last year –– a rough economy, rising costs for fuel and materials, and uninsured, unlicensed contractors getting into the trade and undercutting professionals.

And then the rain. “It’s a quad-whammy,” said Andy Larochelle, the president of Roof Doctor Inc., in Warwick. He estimates that his company will gross about half the earnings it did just two years ago, a plunge from $1.3 million in 2007 to about $650,000 this year. “Six weeks of rain can destroy cash flow,” he said.

House painters count on those sunny days for the lucrative exterior work that supports their businesses year-round. “This is where we make money for the whole season. It’s the exterior work that sets up the interior work for the winter,” said Donald Cardin, president of D’Amico Painting in North Providence.

Despite lining up projects months in advance, the house painters are delayed in getting to the jobs –– or finishing the ones they’ve started. “It’s got us way, way behind, three weeks to a month behind,” Cardin said. “We’ve got jobs we started that we can’t get back to.”

When the sun comes out, Cardin said, he’ll extend the work day as much as possible.

“Sooner or later, the sun’s got to come out,” he said hopefully.

amilkovi@projo.com