Satellite observations and NCOM assessment of the Mississippi-Louisiana-Texas coast following hurricanes Gustav and Ike

In 2008, two major category 2 hurricanes impacted the northern Gulf of Mexico. Hurricane Gustav made a landfall near Cocodrie, Louisiana on September 1, and Hurricane Ike at Galveston, Texas on September 13. Both surface and subsurface changes of sea states caused by these hurricanes were captured by remote sensing. Measurements of sea surface temperature (SST) from MODIS and chlorophyll a (Chla) concentration from SeaWiFS after Gustav and Ike showed evidence of upper-ocean cooling along their tracks and, subsequently, an increase in Chla concentration that is normally not present in the oligotrophic waters of the Gulf of Mexico. In particular, phytoplankton blooms were observed by SeaWiFS in the south of Atchafalaya Bay after Gustav and in the Louisiana Bight west of Mississippi bird-foot delta after Ike. Ike caused large-scale flooding east of Galveston, and plumes of high Chla region near river outlets of western Louisiana coast appeared in SeaWiFS data a few weeks later. Moreover, cloud-free weather in late September afforded true-color imagery from MODIS showing estuarine discharge plumes, sediment transport, and shelf eddies along the Louisiana and Texas coast. These important surface/subsurface phenomena triggered by the hurricanes cannot be understood by remote sensing alone. The high-resolution (~2 km) Navy Coastal Ocean Model (NCOM) developed for Mississippi-Louisiana-Texas (MsLaTex) coast provided additional information, such as sea surface height, degree of vertical stratification, and 3D ocean current vectors, to examine the coastal water responses to hurricanes. We use NCOM to explain physical conditions that caused the plankton blooms and other unusual shelf dynamics after hurricanes Gustav and Ike in the northern Gulf of Mexico.