Isaac was upgraded to a hurricane just before landfall, and actually continued to strengthen as it got closer and closer to the coast. Not only that, it also stalled, and is sitting in basically the same place for 12 hours and counting. The full radar loop of Isaac’s approach from the New Orleans radar is very illustrative for both the intensification and the stalling. It first clipped the Mississippi delta on Tuesday evening, then the center moved offshore just a little, and came ashore again about 70 miles west several hours later. However, hurricanes are large, and damaging effects are always felt very far from the exact center.
As expected, the storm has caused massive power outages (half a million and increasing) and substantial storm surge. The surge was almost perfectly forecast by the National Hurricane Center, and peaked at about 11′ in Shell Beach LA, 8′ in Bay St. Louis MS, 4′ in Mobile Bay AL, 3′ in Pensacola FL, and reports of significant surge in Destin FL. The storm surge will again be a major contributor to the damage, even for a low-end Category 1 hurricane. Storm surge is intentionally no longer a part of the Saffir-Simpson intensity scale.
The rainfall is another big factor, as was very well forecast by HPC. Below is the 24-hour rainfall estimate ending at 6am CDT this morning (so obviously the final values will be higher).
In what seems to be a Circle of Life in the tropics, just as Hurricane Isaac makes landfall and is destined to dissipate into nothing, Tropical Storm Kirk is born far to the east with no threat to land. For more on Kirk’s current position and development, visit Tropical Atlantic Update.
Brian McNoldy
Senior Research Associate
& Author of Tropical Atlantic Update
Follow Brian on Twitter: @BMcNoldy