Slow‑moving hurricanes can dump record rain, regardless of size

Hurricane Harvey’s slow drift over the Gulf of Mexico produced more than 60 inches of rain in parts of Texas, totaling an estimated 27 trillion gallons—enough to fill 40 million Olympic‑size pools. The storm stalled over Houston, overwhelming drainage and turning towns into islands. Size is not the sole determinant of rainfall; a 300‑mile‑wide storm can deliver less than a 23‑mile‑wide one if it moves fast. A 2025 study found that hurricanes over water 10 °F warmer than normal grow rapidly in both strength and radius, as seen with 2024’s Hurricane Helene, which carried moisture into North Carolina’s mountains. Even small, powerful storms like Andrew (90‑mile radius) have caused massive damage, while tropical storms such as Allison produced record rainfall without reaching hurricane strength.