Rainfall records get more extreme the shorter the timeframe you measure, because the most intense bursts of rain on Earth only last a few minutes before the storm producing them either moves on or exhausts itself. Spread that same intensity out over hours, days or months and the numbers change completely, which is part of what makes the full spread of records, from a single minute up to a full year, such an interesting picture of how differently rain can fall depending on the timescale.
The short bursts
The official one-minute world record, recognised by the World Meteorological Organization, is 38mm, set at Barot in Guadeloupe in the Caribbean on 26 November 1970. A separate, widely cited figure of 31mm in one minute at Unionville, Maryland, on 4 July 1956, is often mentioned alongside it and is the accepted US record for that duration, though it sits below the officially recognised world figure.
Extend that out to an hour and the record shifts to the American Midwest. On 22 June 1947, a single thunderstorm dumped 304.8mm, exactly 12 inches, of rain on the tiny town of Holt, Missouri, in just 42 minutes. It remains one of the most extreme short-duration rainfall events ever measured anywhere on the planet, and the fact that it happened in under three-quarters of an hour, in one town, from one storm, is what makes it so remarkable. For a full 60-minute window, the record sits fractionally higher again, closer to 400mm, recorded in Inner Mongolia, China, in July 1975.
24 hours, 12 hours, and multi-day totals
The 24-hour world record belongs to Foc-Foc, a site on the French island of Réunion in the Indian Ocean, where 1,825mm of rain, more than 71 inches, fell in a single day on 7-8 January 1966 during Tropical Cyclone Denise. To put that in perspective, that's more rain in 24 hours than Miami, one of the wettest cities in the continental United States, receives in an entire average year. The same storm also produced the world's 12-hour record at the same location, 1,144mm, nearly 45 inches, in half the time.
Réunion's extreme elevation and steep volcanic terrain play a direct role in why it holds so many of these records. When a slow-moving tropical cyclone parks itself against mountains that rise to nearly 3,000 metres just a short distance from the coast, the moist air is forced upward extremely quickly, wringing out rain at a rate few other places on Earth can match. The island also holds the world records for rainfall over 72-hour and 96-hour periods, and during Cyclone Hyacinthe in January 1980, a single location on Réunion recorded 3,929mm of rain, over 154 inches, across an eight-day span.
Monthly and annual totals
For rainfall measured over a full month or year, the record shifts to a completely different part of the world. Cherrapunji, in the Indian state of Meghalaya, sits on the windward side of the Khasi Hills directly in the path of the summer monsoon, and the topography traps and wrings out moisture on a scale that dwarfs almost anywhere else. In July 1861, Cherrapunji recorded 9,300mm of rain, over 366 inches, in a single month, the highest monthly total ever officially recorded anywhere on Earth. Over the twelve months from August 1860 to July 1861, the same location recorded 26,470mm, just short of 87 feet of rain in a single year, a figure the World Meteorological Organization recognises as one of the highest annual totals ever observed.
Nearby Mawsynram, only about 10km from Cherrapunji, is frequently cited as having the highest average annual rainfall of any inhabited place on Earth, a reminder that these aren't one-off freak events for this particular stretch of hillside. It's simply what the monsoon does there, year after year.