Why Hurricanes Intensify! – Watts Up With That?

Jim Steele

Hurricane Beryl intensified dramatically, strengthening from a tropical depression to a major hurricane in just 42 hours. How could the ocean so rapidly provide enough heat to increase a hurricane’s intensity over such a short time period of time, while travelling northward into cooler sea surface waters?

Hurricane intensification is controlled by 3 dynamics. 1) Energy supplied by sea surface temperatures; 2) Wind shear that increases during El Nino and ENSO neutral years and disrupts the storm structure needed to become a strong hurricane; 3) Ocean Barrier Layers that prevent the storm from sucking up colder subsurface waters that usually prevents intensification, as well as creating a layer of warmer than normal subsurface water that supplies the extra  heat needed to intensify the storms.

Barrier Layers are key for understanding intensification, but rarely accounted for in media fearmongering. Hurricanes intensify when sub-surface Barrier Layers form and block the hurricanes from naturally pulling up cold subsurface water which prevents further intensification. Barrier layers block the upward suction of cold water, as well as providing the extra stored heat that increases intensification.

Barrier Layers form when fresh-water overlays warmer saltier water preventing convection that ventilates subsurface heat and causes subsurface heat to accumulate. In the Caribbean, Barrier Layers commonly form when the freshwater plumes from the Amazon and Orinoco Rivers flow northward into the Caribbean. Those river discharges peak in June, so Beryl’s intensification off the Venezuelan coast in June is not unusual!

Barrier layer formation is patchy based on the coincidence of freshwater flows overlaying warm ocean currents. Barrier layers are short-lived. Thicker barrier layers last 30+ days and thinner ones survive less. Different patterns of the local patchiness of barrier layers are why we see hurricanes intensify in one location along their storm track but only for a short amount of time, a day or less. The thicker the Barrier Layer the greater the storm intensification, and the greater duration of a strong hurricane. 

Beryl will likely decrease in intensity after Tuesday July 2, 2024 as it moves northward outpacing the thicker transport of the barrier layer along the Venezuelan coast. These barrier layer dynamics are just now being more frequently studied, so their effects are seldom discussed, never mind presented in fearmongering media. However read https://news.miami.edu/stories/2018/09/how-does-a-river-plume-influence-hurricanes-in-the-caribbean.html

Ma (2023) “Interannual Variability of Barrier Layer in the Tropical Atlantic and Its Relationship with the Tropical Atlantic Modes” provides a good analysis of Barrier Layers.

Ma wrote, “Since the importance of the Barrier Layer has been revealed, many studies have discussed its formation mechanism in the Atlantic Ocean using observational data. Masson and Delecluse (2001) found that in boreal winter and spring, freshwater from the Amazon River flows through the surface along the northern coast of South America, resulting in a thicker BL in this region.”

As Ma (2023) illustrates, the plume of freshwater that enables that Barrier Layer to develop gradually moves northward into the Gulf of Mexico. The BLT (Barrier Layer Thickness) off the coast of Venezuela where Beryl has just intensified is greatest in winter and spring, then thins as summer progresses and is the thinnest in September-November.

I would predict that Hurricane Beryl will now rapidly weaken as it outpaces the northward movement of the Barrier Layer which supplied the required heat for intensification to a category 4 & 5 hurricane. It is pure randomness that allows a tropical storm’s track to coincide with a thick Barrier Layer, that caused Beryl’s rapid intensification. However, to observe a similar one or two-day period of hurricane intensification was highly unlikely before that age of satellites in the late 1970s, and we will never know how unusual Hurricane Beryl really is historically.