NEW YORK — Things have been heating up in New York City ahead of Valentine’s Day, but forecasters warn the warm weather isn’t here to stay. Temperatures in the Big Apple hit the high 50s Saturday, and even low 60s in some spots, tying the all-time high for the day, according to AccuWeather. The previous record, set just last year in Central Park, was 61 degrees. Forecasters noted that many cities along the East Coast corridor were expected to record toasty temps over the weekend, but they’re also in store for a little bit of weather whiplash. Cooler air, fueled by a storm forming in the South,…