It's a 50-50 chance of thunderstorms Tuesday, and that's the bright side.
1 inch on average, heavier in spots.
2.5-4 inches on average.
2.5-3.5 inches, Mount Pleasant.
4.02 inches, the National Weather Service, Charleston International Airport. (Record rain for the date. Previous record, 2.1).
4.38 inches, heaviest NWS recorded rainfall, 3 miles west of the airport, Dorchester Road area at the Charleston-Dorchester county line.
Source: National Weather Service, Charleston.
A weather front that's been drenching the Lowcountry isn't expected to be nudged out to sea until late Wednesday, when the threat of storms should drop to the usual summer-afternoon 30 percent. The break will come after a stormy weekend that poured more than 4 inches of rain on some spots in the Lowcountry, where it pooled in streets that couldn't drain during "king" tides.
Drought concerns have been allayed by heavy rains so far this month. Official and community weather stations around the Lowcountry have reported large totals, much of its falling over the weekend. Among them are:
9.17 inches - McClellanville
8.40 - McClellanville
8.53 - West Ashley
8.25 - Meggett
7.97 - West Ashley
7.76 - National Weather Service, North Charleston
7.23 - Charleston
6.79 - Johns Island
6.69 - North Charleston
5.55 - Mount Pleasant
Source: Community Collaborative Rain, Hail and Snow Network.
The unusually prolonged deluge is the work of an "old, stalled out" weather front meandering the coastal region, said meteorologist Blair Holloway, National Weather Service, Charleston. An oncoming front should start to push it along Wednesday.
After that, it's back to the normal cycle of scattered, afternoon and evening thundershowers. The unusually high tides are not expected to start slipping back down until Wednesday.
The weekend downpours were spotty enough that a few miles could mean the difference between 2 inches and 4 inches of rain, and led to some freak circumstances.
The Charleston Peninsula was swamped Saturday afternoon by a storm "that came on very, very quickly," said Mark Wilbert Charleston emergency management director. Areas around the peninsula that largely escaped it, such as Mount Pleasant or West Ashley, were swamped by Sunday's rain.
On Saturday, an inch of rain or more fell on the peninsula in little more than an hour. Uncompleted drainage work on routinely swamped Market Street made enough difference that floodwater there receded fairly rapidly.
But in Elliottborough, fewer than two miles away, one block of street flooded to a depth so unusual that longtime resident Arthur Nelson went out with a tape measure to gauge it. Longtime resident Estelle Smalls said she had only seen flood waters deep enough to swamp the parked cars there only once or twice in more than 60 years.
"It was the thunder and lightning that scared me," she said. "I stayed in the house."
Rain and tides
The worst of the rain - 4.38 inches - fell Sunday along Dorchester Road around the Dorchester-Charleston county line and the same amount in McClellanville. An official 4.02 inches fell at the National Weather Service office at Charleston International Airport, Holloway said.
That was the heaviest single day rainfall in Charleston since 2010, said State Climatologist Hope Mizzell.
Tides since Friday have been pumped up by the moon in near-earth orbit and are swelling above the 7-feet level that triggers coastal flood advisories. When the tide is that high in the Lowcountry, rainfall doesn't drain, so street flooding persists.
Tidal charts had predicted high tides of 6 feet or more because of the near moon, or perigee moon. The tides that arrived swept a foot higher because of other weather factors that can't be predicted in advance, said meteorologist Steve Rowley, with the Weather Service in Charleston.
The sudden pounding from of the huge thunderhead that reared over the peninsula on Saturday swamped any number of Charleston streets, as fast as Public Safety, Parks, Recreation and Public Service crews could respond. Cars stranded in the flooded Septima P. Clark Parkway, also known as the Crosstown, were pushed to the side as police detoured traffic from Interstate 26 and the Ravenel Bridge, and barricaded city streets.
"Just about any street that typically closes down was closed down," Wilbert said. Because of the incoming king tide, street flooding "ended up staying around for a lot longer that I have seen it (before). It was a very tough day. We had a lot of folks out working."
On Sunday, streets flooded out in West Ashley, Mount Pleasant, North Charleston and Hanahan among other spots. The heavy Sunday rains fell almost statewide, with a "100 year event" of more than 6 inches falling in a few hours in spots near Greenville, Mizzell said.
When it comes to flooding, it will be a few years before Charleston residents feel much relief. Two major, deep tunnel projects are in the works at two of the most flood-prone spots, Market Street and the Crosstown expressway. The Market Street project isn't expected to be finished before 2017; the Crosstown not before 2020.
Progress has been made on the $25 million Market Street project, said Laura Cabiness, the city's Department of Public Service director. The city already has dug a tunnel deep below the Market and connected it to a pump station at Concord Street.
Crews also have completed three shafts, connecting the street to the tunnel. Now, the city has to replace drainage lines on the street surface and connect them to the shafts. The city will seek bids for that work in about nine months, she said. Construction will take about two years.
City leaders are trying to be sensitive to the needs of Market-area businesses when they schedule construction work, she said, which is slowing the project a bit. But the flooding problem already has improved in the Market. Standing water around the three shafts drains down to the tunnel, Cabiness said, even though the surface lines are not yet connected.
The other major project underway is a massive, $154 million undertaking to improve drainage on the Crosstown expressway.
The first phase of that project consisted of surface work and was finished in 2013, Cabiness said. More surface work still is required, she said. The city will seek bids on that work soon, and construction will take 18 months. It attempted to get that work underway earlier, she said, but the state Department of Transportation shot down the bids the city received because they were higher than engineers' estimates.
The final phase of the project will include a deep tunnel, 12 feet in diameter, below the Crosstown that ultimately will connect to a pump station by the Ashley River.
Reach Bo Petersen at 937-5744, @bopete on twitter or Bo Petersen Reporting on Facebook and Diane Knich at 937-5491 or @dianeknich on twitter.
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