The punishing heat wave that made most of last week nearly unbearable across New York is finally over, but a new week is bringing a new weather danger: the potential for torrential rain and flash flooding.

The National Weather Service warned that between late Sunday and early Tuesday, multiple rounds of thunderstorms could unleash enough rain to cause significant flash flooding across the region.

A flood watch was in effect across the entire area through Tuesday morning.

On Sunday night, as forecasters watched the weather system’s ingredients come together west of New York, they were still uncertain where, exactly, the worst of the rain would fall.

Parts of Pennsylvania and Ohio were also expected to face heavy rain before the worst of the system hits New York on Monday.

In New York, despite some storms on Sunday, forecasters said the heaviest rain was expected by Monday morning and would last throughout the day. New York City, Long Island and suburbs just to the north and east could record up to two inches of rain per hour.

“Please — take this weather seriously,” Mayor Zohran Mamdani of New York said on Sunday. He warned that travel could be treacherous, especially around the morning commute hours.

The governor, Kathy Hochul, said state agencies had been mobilized to respond to any flooding.

When significant rain falls very quickly, areas such as basements, subways and low-lying streets can flood within minutes.

On Sunday, many towns across the New York region were still cleaning up after storms on Saturday night dampened many Fourth of July celebrations.

Tens of thousands homes and businesses across New York, New Jersey, Connecticut and Pennsylvania were still without power after strong winds brought down power lines and tree limbs.