Bonnie heads towards Louisiana
Figure 1: Official track forecast for Tropical Storm Bonnie from the NOAA National Hurricane Center. Official discussion indicates the track guidance has Bonnie heading down the center of the envelope.
Figure 2: Collection of the offshore wind reports from Oceanweather. The counterclockwise wind pattern around Bonnie’s broad low pressure field is observed.
Figure 3: Highest waves, running about 8-10 ft significant, are on the northeast corner of Bonnie on the Florida shelf. Just like the textbooks. The largest waves are on the right side of the hurricane track.
Figure 4: IOOS Overview with the most recent spaghetti plots from this morning’s early cycle (6:00 Z) guidance. The red L marks the center of Bonnie at the time of the forecasts. The many tracks heading northwest from the Low are the ensemble of forecast model runs. The NOAA National Hurricane Center uses this ensemble and others to produce the forecast envelope in figure 1. The current cloud image shown in this google earth image has Bonnie moving northwest along these tracks.
Figure 5: Looking at the Florida shelf behind Bonnie to see where the storm has been, it has passed over 5 gliders deployed for the spill. Two in deepwater at the edge of the Loop Current Eddy, two in shallow water to the left of the track, and one in shallow water to the right of the track. I can’t remember a Tropical Storm with so many gliders deployed since Ernesto in 2006. Behind the storm where the waves are still big, the HF Radar coverage (green arrows) is huge. The 25-hour average nearshore flow is offshore to the southwest.
Figure 6: Now we turn off the clouds so we can look at whats in the water in front of the storm. By the end of the day, Bonnie will have passed over the two gliders currently operating over the drill site, breaking Ernesto’s record for the number of gliders hit by a single tropical storm. We’ll soon have a great dataset for future ocean forecast sensitivity studies in the archive. In front of the storm where the waves are smaller, the HF radar coverage area is reduced. We’ll see this coverage area increase over the course of the day and tomorrow as the storm passes.
Figure 7: Impressed by the weather models and their ability to forecast Bonnie, and the validation data we are are collecting for the ocean models, how are we doing with the ocean models? Here we overlay the SABGOM forecast of sea surface height in color and surface currents as the black arrows. On the shallow side, we see general agreement with the HF Radar behind the storm, where the 25 hour average currents and the storm response in the model are both offshore. On the deep side, we see that the Spray, a Navy Seaglider and a Horizon Marine drifter are all on the eastern side of the Loop Current Eddy where it is undergoing a strong interaction with the Florida shelf break, sending water onshore and east. Tropical Storm Bonnie is passing right over the convergence zone where the offshore flowing waters are meeting the onshore flowing waters on the Florida shelf. Up where the storm is passing now, many small scale features are observed in the model and the HF Radar, they are evolving rapidly, and these comparisons will require a more careful alignment of the observed currents and the modeled currents. We also have many Horizon Marine and Navy drifters in this region. All these will help sort out the impact of this tropical storm on the complicated flows off Louisiana.