Harley Gibson, 1½, is scooped up by her father Darren Gibson as they play during the New Hampshire Fisher Cats game Sunday afternoon at Northeast Delta Dental Stadium in Manchester. The two were up visiting from Weymouth, Mass., and took in their first baseball game.

CONCORD — New Hampshire’s stretch of warm weather is expected to continue through the middle of the week.

Temperatures Sunday reached 80 degrees for the fourth straight day in southern New Hampshire as the Granite State continued to approach summer-like weather.

“It was a pretty slow and cool and wet start to spring,” said William Watson, a meteorologist with the National Weather Service in Gray, Maine.

While air temperatures are hovering a few degrees above normal, New Hampshire lakes and rivers are still running cold enough for the National Weather Service to issue a water safety advisory. Temperatures in lakes and rivers are still running only in the mid-to-low 50s.

Although the air has been warmer lately, Watson said the sun — which hasn’t shined a lot on the Granite State so far this spring — also plays a large role in warming up lakes and rivers to temperatures safe for swimming.

“The full sunlight will definitely help,” Watson said. “This is really one of the best weekends we’ve had so far.”

Although surface temperature readings were reported as high as the upper 60s, it’s much colder beneath the surface; the Weather Service listed the official temperature at 56 degrees.

“When the water is that cold, even good swimmers could be incapacitated quickly,” Watson said.

More sun was expected Monday, followed by clouds and a chance of rain Monday night into Tuesday. Even with the rain, Watson said, the forecast called for temperatures in the mid-to-upper 70s on Tuesday and Wednesday.

Manchester hit 80 degrees for the fourth straight day Sunday, and Concord reached 80 degrees three consecutive days, just missing out when Thursday’s high hit 79 degrees, Watson said. Prior to Thursday, Concord had had only three days with high temperatures of 80 or higher in 2019, Watson said.