A stretch of wet weather is forecast into the weekend, with showers and some thunderstorms forecast before a possible deluge from a strengthening Tropical Storm Joaquin.
A cold front forecast to pass through the region Wednesday started to wring moisture from the air Tuesday night, and rain is forecast to continue Wednesday.
At Baltimore-Washington International Thurgood Marshall Airport, 1.34 inches of rain fell by 10 p.m. Tuesday, with nearly an inch of that between 9 p.m. and 10 p.m. At 11:30 p.m. a flash flood warning was issued for Baltimore County and northwest Harford until 2:30 a.m.
As much as 2 inches of rain or more could fall across Central Maryland by Thursday morning, according to the National Weather Service.
Flash flood watches and warnings are in effect for Western Maryland. Radar suggested 2 inches of rain had already fallen by late Tuesday night, with another 1-3 inches possible there overnight.
Aside from the moisture, the cold front is forecast to drop temperatures by about 15 degrees come Thursday. Highs are forecast to fall to the lower 60s, instead of the upper 70s.
But the bigger concern could be Joaquin.
The storm is moving slowly westward toward the Bahamas, about 400 miles northeast of those islands, according to the National Hurricane Center. It is gaining strength, with maximum sustained winds of 65 mph, and is expected to become a hurricane Wednesday.
Forecasts suggest it will take a turn toward the north Saturday and approach the North Carolina coast by Sunday, a slower trajectory than previously predicted. It is forecast to remain a hurricane through at least Sunday.
But models are mixed on whether it will remain out at sea or come in to the coast. Some models suggest high pressure to the north and east over the Atlantic could steer the storm into the mid-Atlantic, while others keep it out to sea.
Forecasters at the weather service's Baltimore/Washington forecast office called it "a fragile and potentially high impact forecast" for the weekend. A prolonged period of rain is possible, some of it "quite heavy," they wrote.
"The details of how significantly, and even if, that storm will impact the Mid Atlantic will become clearer as the week progresses," they wrote. "If it does impact us, a period of time within late Friday through Monday is most likely."
Weather service models predict more than 4 inches of rain for most of the state over the next week.
Baltimore public works officials are already urging residents to clear trash, leaves and other debris from storm drains to prevent flooding.
One popular weather blog, Foot's Forecast, is meanwhile raising concern that Joaquin could pack as strong a wallop as Isabel did in 2003.
The site highlighted one model showing a Category 2 storm making landfall in North Carolina before churning up the Chesapeake Bay. Most scenarios would require the hurricane center to shift its forecast cone to the west, closer to the coast.
"Our confidence for these scenarios is not high, but the uncertainty underpinning the entire forecast is very high, hence the urgency to make clear the potential risks," Foot's forecasters wrote.
Rain is needed across much of the state. "Abnormally dry" conditions are present across the western half of the state, including most of Howard and Anne Arundel counties, as well as some patches of the Eastern Shore, according to the U.S. Drought Monitor.
About half an inch of rain had fallen this month at BWI through Monday, more than 3 inches below normal. Most of that fell Sept. 12.