As Hurricane Ida reversed the course and weakened the Mississippi, Sunday saw the incredible power of Hurricane Ida.
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After Ida, a Category 4 hurricane that experienced rapid intensification and made landfall on Sunday afternoon, the river flowed temporarily from south to north. According to the U.S. Geological Survey, a Belle Chasse river gauge, located just southeast of New Orleans, witnessed the remarkable about-face of Mississippi River.
In the days before Idas arrived, approximately 350,000 cubic feet (9.910 cubic meters), of water were being released by Mississippi. The water moved upstream at a rate that was 40,000 cubic feet (1.132 cubic meters) per sec. This is a huge amount of water to turn around. Ida is expected push 16 feet (5 m) of storm surge into the interior, with the maximum inundation affecting an area that extends from Port Fourchon, the petrochemical hub, to the mouth of Mississippi. This is evident by the river's turnaround.
This is a phenomenon that we have seen in other storms, such as Hurricane Florence in 2018. This is what we call compound flooding. Storm surge pushes water into areas where rain is falling, causing it to cause flooding. The rain can't drain because of the water pushing onto the shore.
As Ida continues to move into the evening, this could be a greater concern. In its latest forecast discussion, the National Hurricane Center pointed out that Idas' forward motion has slowed. This means that rain bands can sweep across a location repeatedly. This could lead to more flooding.
Ida, despite spending many hours on the ground, has not diminished in strength. Ida still packs winds of 130 mph (209 km/h). This is due in part to the brown ocean effect. It occurs when storms can absorb moisture from the ground and retain their strength as they move inland. The effect even sustained a tropical storm all the way to Great Lakes. However, it was in a weaker form than Ida.
Southeast Louisiana is a case where land may be too generous. The region is dominated by bayous and barrier islands and has become more fragmented and watery as a result of subsidence and the rise in sea levels due to oil and gas burning. Scientists have deemed the worst-case scenario for Louisiana, and the Mississippi River has been contained by the levee system.
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In the long-term, there are many reasons to be concerned about this. It means that Ida has plenty of warm, shallow waters to fuel it as it moves northward. Even though the Mississippi has now reversed its course, there is still a lot of damage to the storm's system.
