Fourth of July celebrations are being threatened by the first named storm of the season, Tropical Storm Arthur. The storm is expected to reach hurricane strength by Friday in North Carolina.

Storms and heavy rain are forecast Thursday and Friday as a front of cool, dry air and Tropical Storm Arthur converge over the Mid-Atlantic, disrupting Fourth of July fireworks plans in Ocean City but clearing out the heat and humidity for the holiday weekend.

Even though Arthur is expected to pass well off the coast, the storm prompted Ocean City officials to reschedule the town's fireworks show from Friday to Saturday. Lifeguards also cautioned that the storm would kick up dangerous surf and rip currents.

Across the state, the hot, moist air this week is forecast to fuel storms with damaging winds and heavy downpours throughout Thursday and potentially into Friday. But it could clear out in time to salvage much of the holiday and make for a sunny and cool weekend.

Arthur prompted hurricane warnings for North Carolina's Outer Banks, as it was expected to skirt the coast early Friday before heading northeast out to sea, pushed away by the cold front. The storm is expected to be at least 100 miles off the Delmarva coast as it passes by Friday but still could bring winds of 15-20 mph with gusts as high as 30 mph into Friday evening.

At the beach, storms are likely from Thursday afternoon through at least midday Friday, likely hampering setup efforts for Ocean City's fireworks.

"Due to the passing storm and the probable residual effects of the weather, including wind and rain, it would be logistically challenging to hold the fireworks shows on Friday," Mayor Rick Meehan said in a statement. "We are expecting some wet weather on Thursday night and into Friday morning, which makes it nearly impossible to set up the fireworks show on the beach in enough time for Friday night."

Ocean City Beach Patrol Captain Butch Arbin said he expects dangerous swimming conditions, which have contributed to the deaths of two teenagers already this season in Ocean City. Along with heavy surf, the storm can exacerbate rip currents that carry swimmers away from shore.

According to the United States Lifesaving Association, signs of a rip current include a channel of churning, choppy water; an area with a notable difference in water color; a line of foam, seaweed, or debris moving steadily seaward; or a break in the incoming wave pattern.

In the Baltimore area, stormy weather is expected throughout Thursday and into Friday morning, but partly cloudy skies and lower temperatures and humidity are expected in time for fireworks Friday evening.

Heat index values Thursday could approach 100 degrees, with highs around 90 and high humidity, but highs are forecast to drop to the lower 80s Friday.

Clear, sunny skies and highs in the mid-80s in Baltimore and the upper 70s in Ocean City are forecast for Saturday and Sunday.

Baltimore Sun reporter Jake Nevins contributed to this article.

sdance@baltsun.com

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