A flash flood warning is in effect until 9 a.m. for Boston and several communities south of the city, including Brockton, Quincy, and Randolph, officials said Thursday morning. The National Weather Service also issued a flood watch that will remain in effect until 4 p.m. for Rhode Island and eastern portions of Massachusetts and Connecticut.

Communities south of Boston have seen as much as 4 and a half inches of rain, with a flash flood warning still in effect.

An historic amount of rain fell in parts of Massachusetts Thursday, unleashing floods in towns south of Boston.

Here’s what to know about the deadly flooding, the colossal weather system that drove it in and around Kerr County, Texas, and ongoing efforts to identify victims.

“This isn’t just a technical issue — it’s a matter of public safety,” meteorologist Ted McInerney says. “Flash flood warnings and accurate rainfall estimates rely heavily on clear low-level radar scans. Other than that, we watch rain gauges and reports.”