Torrential rains from Tropical Storm Imelda swamped parts of southeast Texas, bringing record-setting rainfall totals and damaging flash floods to Houston and Beaumont. The slow-moving system—which moved just 3 miles (5 kilometers) per hour at times—pulled in heat and moisture from the Gulf of Mexico to fuel extreme rainfall over land.
The map above depicts satellite-based measurements of rainfall from 2:30 a.m. Central Daylight Time on September 17 to 2:30 a.m. on September 20, 2019. The brightest areas reflect the highest rainfall amounts, with some places receiving as much as 30 inches (75 centimeters) or more during this period (the top of our scale). The measurements are a product of the Global Precipitation Measurement (GPM) mission, which is a partnership between NASA, the Japan Aerospace Exploration Agency, and five national and international partners.
The rainfall totals are regional, remotely-sensed estimates. Each pixel shows 0.1 degrees of the globe (about 7 miles at the equator), and the data are averaged across each pixel. Individual ground-based measurements within a pixel can be significantly higher or lower than the average.
Forecasters had called for some locations to receive as much as 45 inches of rain. According to the National Weather Service, some stations east of Houston were nearly there already. As the storm was winding down on September 20, the gauge at North Fork Taylors Bayou measured 43.39 inches of rain. See a summary of storm totals by clicking here.
Data for the map comes from the Integrated Multi-Satellite Retrievals for GPM (IMERG), a product of the GPM science team. IMERG compiles precipitation estimates from passive microwave and infrared sensors on several satellites, as well as monthly surface precipitation gauge data, to provide precipitation estimates between 60 degrees North and South latitude.
The storm is reminiscent of Hurricane Harvey, which dumped massive amounts of rain over the same area in 2017. However, Imelda’s rainfall totals are not quite as high, and the area affected is not as large as it was for Harvey, according to a report from The Weather Channel.
NASA Earth Observatory image by Joshua Stevens, using IMERG data from the Global Precipitation Mission (GPM) at NASA/GSFC. Story by Adam Voiland.