Rainfall Forecast/River Flood Risk Associated with Barry
Discussion: The heavy and possibly extreme rainfall from Tropical Storm Barry will cause accelerated river rises centered on eastern Louisiana. Current river forecasts indicate crests will occur either late Saturday or early Sunday along the Atchafalaya River near Morgan City and the Mississippi River from Baton Rouge southeastward to New Orleans. Moderate flooding is indicated by river gauge forecasts except major flooding at Baton Rouge. The forecasts are preliminary.
There is a lot of discussion as to whether Barry can produce as much rain as forecast by models given Barry’s poor organization this morning. The answer is YES! Barry will become better organized today/tonight before moving inland tomorrow. The key to the forecast is the better organization is taking place over 85-86F water in the northern Gulf of Mexico. The potential energy eventually leading to deep convection and heavy rainfall associated with water temperatures this warm completely support the excessive rainfall forecasts. The slow-moving nature of Barry today and through the weekend adds duration to the mix which further supports the excessive rainfall forecasts. Harvey (2017) and Florence (2018) produced 50 in. of rain due to their slow movement caused by blocking high pressure after crossing 85-86F water prior to moving inland. The water temperature beneath Barry in the northern Gulf is key to the (rainfall) forecast.
The slow moving nature of Barry will being heavy rains northward to the Tennessee Valley next week with remnant heavy rains into the Northeast Corridor later next week.
Fig. 1: NOAA 7-day rainfall forecast indicates >15 in. across southeast Louisiana and 3-5 in. as far north as the Tennessee Valley next week.
Fig. 2: NOAA Significant River Flood Outlook for the Lower Mississippi River.
Fig. 3: NOAA greatest flash flood risk over the next 3 days forecast.