The National Weather Service issued flash-flood warnings on Wednesday evening for parts of Massachusetts and Delaware as slow-moving storms brought intense downpours to the Northeast. In Massachusetts, the Boston forecast office warned residents of Lowell, Lawrence and Haverhill—along with much of northwestern Essex and Middlesex counties—to avoid low-lying roads and underpasses until the alert expires at 9:00 p.m. EDT. Forecasters said rapid rises on small streams and urban drainage systems were possible. Farther south, the agency’s Mount Holly, New Jersey office placed Newark, Brookside and Hockessin, Delaware under a flash-flood warning until 11:00 p.m. EDT. Motorists were urged not to drive through water-covered roadways, with localized totals capable of overwhelming storm drains. The warnings come amid a broader pattern of severe late-summer thunderstorms sweeping the Mid-Atlantic, prompting officials to monitor additional watches for hail and damaging winds through the evening.