The National Weather Service issued a series of severe-thunderstorm warnings for northeastern Massachusetts and southern New Hampshire on Wednesday afternoon, effective until 5:45 p.m. EDT. The alerts cover Middlesex, Essex and Worcester counties in Massachusetts as well as Hillsborough, Rockingham and Merrimack counties in New Hampshire, including the cities of Lowell, Ayer and Pepperell. Forecasters warned of wind gusts reaching 60 mph, quarter-size hail and frequent lightning. Emergency officials advised residents to seek immediate indoor shelter, monitor local weather outlets and be prepared for possible power outages as the fast-moving storms track through the region.