A flash flood warning was in effect in New York City until 9:45 p.m., and New Jersey Gov. Phil Murphy declared a state of emergency. Middlesex, Morris and Somerset counties remained under a flood warning until 7:15 a.m. Tuesday.

Tropical rainstorm along Gulf Coast; flood threat for the Northeast; storms in the Midwest; dangerous heat from coast-to-coast

Several NYC subway stations flooded on Monday night after rain drenched parts of the city, causing severe delays and even closures.

The heavy downpours wreaked havoc across the city with footage showing commuters overwhelmed by floodwaters in various subway stations.

Heavy rains and flash flooding in the northeast have caused two deaths in New Jersey. More rain is expected through mid-week for portions of the eastern and central U.S.

NYC could be in play for another heat wave this week, with the potential for more heavy rain, storms and flash flooding due to the hot and humid conditions.

Both westbound and eastbound lanes have since reopened. Crews were cleaning up mud, repairing the road and damaged dividers and repaving the roadway. They also painted new stripes in the eastbound lanes. All of these repairs are happening after Monday night's storm that flooded streets and damaged homes, roads and cars.

Flash floods are occurring across the U.S., from Texas to New Jersey. Here's what you should know as risks escalate.