HMN 2025: How ‘stress mark’ within the Gulf might drive hurricane energy

Driven by excessive temperatures within the Gulf, Hurricane Ian quickly intensified from a Category 3 to Category 5 earlier than making landfall in Southwest Florida on September 28, 2022. The lethal storm caught many unexpectedly and have become the most costly hurricane in state historical past.

Now, researchers from the University of South Florida say they’ve recognized what could have precipitated Ian to develop so shortly. A powerful ocean present known as the Loop Current did not flow into water within the shallow area of the Gulf. As a end result, subsurface waters alongside the West Coast of Florida remained unusually heat through the peak of hurricane season.

The findings, published in Geophysical Research Letters, could also be used to make extra correct predictions about hurricane depth.

In the Gulf, fast intensification usually happens over deep waters that may retailer considerable warmth power. But Hurricane Ian was totally different. As the storm neared landfall, it intensified over the shallow West Florida Shelf, which is generally stored cooler because of ocean currents.

This anomaly intrigued researchers on the USF College of Marine Science’s Ocean Circulation Lab.

“We needed to grasp how the nice and cozy subsurface waters of the West Florida Shelf had been in a position to persist all summer season,” mentioned Yonggang Liu, affiliate professor and lead writer of the latest study. “What had been the situations within the Gulf that allowed these temperatures to develop within the first place?”

Liu and his crew turned to knowledge they’ve gathered over a number of many years by way of the Coastal Ocean Monitoring and Prediction System (COMPS), an array of floor buoys and bottom-mounted moorings throughout the shelf. COMPS offers real-time measurements of ocean currents, salinity, and water temperature to the scientific group.

The researchers discovered that if the Loop Current reaches an space close to the Dry Tortugas, which they name the “stress mark,” it may well flush heat waters from the West Florida Shelf and substitute it with chilly water from deeper areas of the Gulf. This stress mark is where the shallow contours of the seafloor converge, forcing chilly water to the floor in a course of generally known as upwelling.

In the months main as much as Hurricane Ian, the Loop Current didn’t attain the stress mark, leaving the waters on the shelf unmixed, which precipitated each the floor and subsurface waters on the West Florida Shelf to stay heat all through summer season.

“Typically, there’s a mixing of the water column where hotter floor waters work together with the underlying, typically cooler subsurface water,” mentioned Liu. “But on this case, the shelf water was not in a position to calm down as a result of the Loop Current didn’t provoke any upwelling.”

The temperature of the subsurface layer of water is essential for forecasters to watch, in response to Liu, as sea floor temperatures solely give a glimpse into the warmth accessible for hurricanes. Prior to Hurricane Ian, floor waters had been just one–2°C hotter than common, whereas the subsurface waters had been 2–3°C hotter.

“By not together with the subsurface water temperature in models and forecasting, we aren’t getting the whole image of the water column and the potential power for hurricanes,” Liu mentioned.

Measurements made by COMPS allowed Liu and his colleagues to look at the long-term pattern of ocean temperature and currents on the West Florida Shelf, together with the affect of the Loop Current on the area.

This study highlights the significance of monitoring subsurface temperatures for warmth content material alongside the coast, and factors to the worth of coastal remark packages for the resilience of the state and nation. COMPS companions with NOAA’s Integrated Ocean Observing System (IOOS) by way of the Southeast Coastal Ocean Observing Regional Association (SECOORA) to enhance such oceanic observations within the Gulf.

“The extra real-time observations now we have of the whole water column, the higher predictions we will present, and the safer our communities will likely be,” Liu mentioned. “This sort of monitoring offers extra full knowledge to foretell depth of future storms.”