Harvey’s Approach Brings Potential Severe 5-Day Rain Event For Texas and Louisiana

21 August, 2017

For the third time in less than one month, powerful thunderstorms have dropped torrential rains in excess of 6 inches over Kansas City, Missouri. In the most recent event, a frontal system dropping down over the U.S. midsection encountered a very heavy load of atmospheric moisture streaming in off a much warmer than normal Gulf of Mexico. The result for Kansas City was the production of a towering boomer that dropped 10 inches in just one night.

Such an intense downpour turned roads into rivers and forced numerous residents to take refuge on rooftops as the waters rose once again. By morning, more than 130 water rescues had been called in across the city.

(NOAA predicts heavy rainfall for Texas and Louisiana over the coming week. Image source: NOAA.)

But this particular extreme event may be a simple prelude for what’s to come as the remnants of Harvey sets its sights on the Texas and Louisiana Gulf Coasts. Harvey is expected to strengthen into a tropical storm or weak hurricane over a very warm and moist Gulf of Mexico within the next 48 hours. Models then predict that it will combine its substantial moisture load with that of the frontal system responsible for such severe flooding in Missouri last night.

Already NOAA is predicting some very significant rainfall amounts over the coming days for the Texas and Louisiana coastal regions (see image above). And Harvey represents a considerable rainfall potential given the fact that it is expected to stall over Texas and Louisiana for the better part of 5 days. With regards to NOAA rainfall predictions, it is worth noting that extreme local precipitation values have significantly exceeded NOAA predictions recently in the case of the most severe thunderstorms.

(2 PM EST assessment of Harvey’s path and potential for restrengthening. Image source: The National Hurricane Center.)

One possible spoiler for Harvey reforming is an upper level low swirling just southeast of Texas. This low could rip Harvey apart. But if this happens, that system would tend to also direct Harvey’s moisture toward Texas, Louisiana and Alabama. In which case, strong rainfall potentials are also likely. However, the National Hurricane Center expects this upper level low and associated squalls to move toward the north and west — generating rainy conditions for Texas and Louisiana ahead of Harvey and creating space for a more powerful and heavily moisture laden storm to form.

Lower than normal precipitation totals in the region of Coastal Texas during the past couple of months may help to alleviate flood potential if the rains from Harvey remain on the somewhat lighter side (2-4 inches) and if the system continues to be disorganized. A more organized system would tend to bring heavier precipitation totals. However, it is worth noting that during recent years, much warmer than normal sea surface temperatures have combined with a warmer atmosphere to spike heavy rainfall totals. A result of human-forced climate change due to ongoing rampant fossil fuel burning.

Links:

NOAA

The National Hurricane Center

Historic Flooding Leaves One Dead

Over 130 Calls Made to Kansas City Fire Department Amid Life Threatening Flooding Overnight

Hat tip to Wharf Rat