Rain bomb. It’s a new kind of severe rainstorm that’s capable of overwhelming a city’s flood-handling capabilities in just an hour or two. Of generating 2-inch-plus per hour rainfall events in odd places and at unexpected times. A type of severe storm that’s been enabled by all the added heat and atmospheric moisture loading resulting from human-forced climate change.
(High levels of atmospheric water vapor over the northeastern Gulf of Mexico is fueling the potential for severe, damaging and life-threatening rainfall events across the Gulf Coast this week even as numerous severe flood events occur across the globe. Image source: Earth Nullschool.)
Lately, due in large part to an atmosphere and ocean surface that’s about 1.2 degrees Celsius hotter than 1880s values and related added atmospheric moisture, the powerful, damaging, and life-threatening rain bombs have been going off hard and heavy across the globe. Last week, Ellicott City was hit, killing one and generating damage that will likely take years to repair. Yesterday, about 21 people lost their lives in a freak flood that dumped 20 inches of rain over part of Macedonia. In Sudan on Saturday, the Nile reached its highest levels in 100 years as thousands of homes were destroyed and more than 75 people lost their lives. In Karachi, Pakistan this weekend, 50 percent of the city is without power and ten people have lost their lives due to flooding. In India over the past two weeks, more than one million people have been displaced and 100 killed in devastating floods. And now, a very hot Gulf of Mexico appears to be hurling a number of similarly powerful storms at the U.S. Gulf Coast.
Severe Gulf Rainstorms Begin
There’s a hell of a lot of heat and moisture available to fuel storms over the Gulf of Mexico right now. And this region where ocean surfaces exceed 90 degrees Fahrenheit (running from 30 to 33 C, or 1 to 3 C above average) over a broad swath is just now starting to toss some extremely powerful rain bombs at nearby states.
(26 inches of rain fell over a portion of the Gulf of Mexico in one 24-hour period just west of northern Florida. Over the coming week, this moisture is expected to shift northward over Lousiana, Mississippi, and the Florida Panhandle. Image source: Jesse Ferrell at Accuweather.)
Strong convection is blowing up from the hot surface of these waters and exploding into thunderstorms. Already, big rain bombs are starting to fall out over the Gulf or streaming onto shore. As of yesterday, one of these systems produced more than 26 inches of rain in just one 12-hour period. That’s an average of about 2.2 inches of rainfall per hour for 12 hours running, an amount of water that would cause extremely severe flooding if it fell on a U.S. city.
Today, these rain bombs began roaring ashore over the Florida Panhandle. A series of such systems dumped 20 inches of rain near Dekle Beach, Florida even as powerful storms firing near Pinland and Perry dropped 16 inches.
(Earlier today, 20 inches of rain fell near Dekle Beach, Florida even as totals near 16 inches fell between Pinland and Perry. Image source: Jesse Ferrell at Accuweather.)
To be clear, these are just thunderstorms associated with a very hot and moist weather pattern over the Gulf — but they’re producing rainfall amounts usually seen in strong tropical cyclones. Meanwhile, National Weather Service radar shows strong storms continuing to cycle into this region of Florida even as south Florida is hammered by heavy storms and intense squalls swirl over the western Panhandle, Alabama, and Mississippi.
More Severe Rain on the Way, but the Rain Bombs Themselves are Tough to Predict
Over the coming week, the potential for continued heavy storms is high. NOAA’s precipitation forecast model shows rainfall potentials for the region in the range of 5-10 inches for some locations over the coming week. It’s worth noting, however, that NOAA model runs have often not captured the full potential peak rainfall totals in some recent severe events. To this point, it’s also worth noting that forecasting rain bombs can be difficult, particularly so during recent years. Monitors like NOAA can track the underlying conditions, but it’s generally tough to see exactly where the big precipitation spike will occur until perhaps a few hours before the rain starts falling.
Part of this prediction difficulty is likely due to the fact that the added atmospheric moisture loading — 8 percent since the 1880s and 5 percent since the late 1970s — due to global warming has increased instability to the point where new, and less well understood, types of weather are being generated. These days, there are new kinds of thunderstorms ranging the globe, and there’s a lot we don’t understand about them.
Hat tip to TodaysGuestIs
Hat tip to Andy in San Diego