Sunday’s relatively balmy temperatures may herald what forecasters said could be one of the warmest first weeks of February on record.

The day’s top temperature reached the high 40’s, dropping to the low 40’s at night, said the National Weather Service, hardly the kind of numbers normally linked to the last day of January.

And it gets better.

“It’s going to be a pretty mild week,” Carlie Buccola, of the service’s Upton office, said, adding that the average temperature for the first five days of February this week, just above 40 degrees, comes close to 42.2 degrees reached in 1991, the highest average for the week since 1984, the year when records have been kept at Islip.

All told, the week could bring temperatures that are 10 to 15 degrees above average, she said.

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Monday, though dampened by an afternoon shower, will clear 52 degrees during the day, dropping to 34 degrees under cloudy skies at night.

More of the same is expected for Tuesday, which should see mostly sunny skies and a high temperature of 47 degrees. At night, Buccola said, there’s a 30 percent chance of rain and temperatures dip to 38 degrees.

Wednesday will likely be wet, with an 80 percent chance of showers but a high of 56 degrees. Nighttime temperatures drop to 39 degrees.

Buccola said Thursday is calmer and still unseasonably warm, reporting a high of 45 degrees and plenty of sun but leading to a nighttime chill of 29 degrees.

Friday marches in with weather more like a typical February day: partly sunny with a high of 39 degrees and a low at night of 28 degrees.