People may feel like they're moving quickly from the frying pan to a swimming pool in parts of New Jersey, New York and Pennsylvania this weekas sweltering temperaturesin the mid-to-high 90s give way to a deluge of torrential rain and potential flash flooding. Daily record high temperatures were set at LaGuardia Airport (99 degrees) and Atlantic City, New Jersey (97) on July 30, while heat indices – what the heat feels like – reached triple digits in some areas, the National Weather Service said. But as the heat lingered into the evening,the service began posting flood watches. By the afternoon of July 31, more than 50 million people in the region are forecast to be under a flood watch. State and local officials warned the region's residents to prepare in advance for potential flooding, with as much as 3 inches of rain expected, and even higher amounts possible in isolated locations. Parts of central and western New Jerseycould see more than 4 inches of rain in a short period of time, with rain falling at rates greater than two inches an hour, which could lead to flash flooding, the weather service said. "There is increasing confidence for a period of moderate to locally heavy rainfall Thursday afternoon and Thursday night as a frontal boundary remains south of the region and a wave of low pressure travels along the front," stated aJuly 30 forecast discussion from the weather service. "An axis of repetitive torrential rainfall and embedded thunderstorms is likely" on Thursday afternoon and evening, the weather service said. The entire region is under an excessive rainfall outlook. A moderate risk of heavier rains is forecast over New Jersey, eastern Pennsylvania and Maryland, with a lower risk of excessive rain stretching from northern and eastern Virginia in to southern Massachusetts. Most of the rain is forecast to fall in as little as 3-6 hours. A small chance of heavier rain and flooding could pose "an elevated threat to life and cause significant disruptions to transportation, flood underground infrastructure and basements and first floors of residences and businesses," with water rescues needed, the weather service said. "We're preparing for a serious storm tomorrow evening," New York CityMayor Eric Adams said on X on July 30. The city posteda travel advisory for Thursday and Fridayand asked people to avoid traveling if possible. "Roads may become flooded during the evening commute," the city warned. "Set up flood prevention tools early," Adams' office warned in an X post. "If you live in a basement, prepare to move to higher ground." Individuals in the region should have "several reliable ways to recieve flood-related watches and warnings at all hours," AccuWeather stated on July 30. "Roads that appear to only have a small amount of water running across them may be deceiving, especially at night when the visibility is reduced," warned Alex Sosnowski, AccuWeather senior meteorologist. "Six inches to a foot of moving water can cause small vehicles to be pushed along. With 1 to 2 feet of water, larger SUVs can float. At the very least, vehicles can sustain severe water damage." The New York State Division of Homeland Security and Emergency urged residents to sign up for emergency and weather alerts bytexting their county or borough to 333111. "As the forecast shifts from extreme heat to heavy rains, I am urging all New Yorkers to stay vigilant and use caution through the end of this week,"Governor Kathy Hochul said in a news release."State agencies are on standby for heavy downpours and localized flooding and will be monitoring the situation in real-time to ensure the safety of all New Yorkers in the path of the storm." The exact location where the front stalls will be pivotal in where the heaviest rain falls, the weather service said. For now the highest probability is just to the southwest of the New York City and New Jersey metro area, the weather service warned, but any shift northward would move the area of greatest potential rain closer into the city. As therecent flooding in Texas Hill Country showed, forecasts often struggle to pinpoint the exact location where weather systems will interact with each other in the atmosphere above a region and drop the greatest rainfall. It's a conundrum experts have been working to resolve in computer forecast models. As of 8 p.m. on July 30, the greatest probabilities for more than 4 inches of rain through Aug. 2 were in the following locations: Mount Holly, NJ - 34% King of Prussia, PA - 31% West Chester, PA - 24% Trenton, NJ - 22% West Milford, NJ - 10% The greatest chances for more than 3 inches of rain were in: Trenton, NJ - 53% West Chester, PA - 43% Mount Pocono, PA - 34% Doylestown, PA - 33% West Milford, NJ - 33% New York City - 21% Haverstraw, NY - 27% Sherman, CT - 20% Conditions are forecast to begin improving on Aug. 1and return to near normal. Dinah Voyles Pulver, a national correspondent for USA TODAY, writes about climate change, violent weather and other news. Reach her at dpulver@usatoday.com or @dinahvp on Bluesky or X or dinahvp.77 on Signal. This article originally appeared on USA TODAY:Heavy rain, flash flood forecast in New Jersey, northeast