A new study by University of South Florida researchers shows a slowdown in the loop current that funnels warm water into the Atlantic Ocean helped intensify Hurricane Ian in 2022.
The current failed to reach the continental shelf off Florida's Gulf coast. It couldn't reach the Florida Straits, where it creates the Gulf Stream that flows northward in the Atlantic. That meant warmer water staying in the Gulf fueled the hurricane, which briefly reached Category 5 before plowing into Lee County at Category 4.
Yonggang Liu , lead author of the study and director of the Ocean Circulation Lab at USF's College of Marine Science, says just before Ian made landfall, the loop current seemed to be stuck in neutral.
That meant colder, deeper water didn't flow in the shallow continental shelf, called the West Florida Shelf. So Gulf waters remained unusually warm, feeding the intensity of the hurricane.
Liu says the loop current never made it to a critical point near the Dry Tortugas. That's where it can flush warm waters from the West Florida Shelf and replace it with cold water from deeper regions of the Gulf.
"Typically, there is a mixing of the water column where warmer surface waters interact with the underlying, often cooler subsurface water,” said Liu. “But in this case, the shelf water was not able to cool down because the loop current did not initiate any upwelling.”
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But he said it's difficult to predict the behavior of the current.
"The loop current behavior is very chaotic, not predictable at this time," Liu said. "To my knowledge, nobody can predict. It's not that easy."
He says more ocean temperature monitors need to be built offshore to be better able to predict the strength of hurricanes.
"This needs to be expanded. Right now, we only implement on two moorings," he said of the sensors. "This needs to be expanded to more locations, and not only to our shore. We need to expand it to other coastal oceans."
The temperature of the subsurface layer of water is important for forecasters to monitor, according to Liu, as sea surface temperatures only give a glimpse into the heat available for hurricanes. Prior to Hurricane Ian, surface waters were only 1 to 2 degrees Celsius warmer than average, while the subsurface waters were 2 to 3 degrees warmer.
“By not including the subsurface water temperature in models and forecasting, we are not getting the entire picture of the water column and the potential energy for hurricanes,” Liu said.
