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.

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

Flooding caused delays on multiple New York City subway lines Monday as torrential rain pummeled the Tri-State Area.

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

Severe flash flooding struck New York City, Westchester County, Staten Island, and Rockland County, Bergen, Essex, Hudson, Passaic

While FEMA has improved the accuracy and accessibility of the maps over time with better data, digital tools and community input, the maps still don't capture everything.