As Tropical Storm Idalia moves across the Caribbean and toward the Gulf of Mexico, forecasters are closely monitoring its track and the potential for rapid strengthening. The storm is expected to make landfall in the Florida Panhandle on Wednesday, August 30, and possibly become a major hurricane. The unusual combination of high ocean temperatures and wind shear due to El Niño climate patterns makes the current hurricane season particularly difficult to predict.
The role of ocean temperature
One of the key factors affecting Idalia’s forecast is the exceptionally high sea surface temperatures in the Gulf of Mexico. While the Gulf is typically warm in late August, this summer’s temperatures have been record highs and well above average. On Monday, as Idalia passed near Cuba, sea surface temperatures reached nearly 86 degrees Fahrenheit (30 degrees Celsius). As the hurricane moves northward, it will encounter even warmer waters and by Wednesday morning, sea surface temperatures will be near 88 degrees Fahrenheit (31 degrees Celsius).
The heat is not only concentrated near the surface, but also spreads deep into the upper layer of the ocean, called the thermocline. This stored heat serves as fuel for the storm, providing it with the energy it needs to strengthen.
The effect of ocean temperature on a storm
Warmer ocean temperatures increase the amount of water vapor available to a storm. Warmer air is able to hold more water vapor, resulting in more clouds and increased storm rotation. In addition, warmer ocean temperatures can lead to more intense precipitation.
The role of wind shear
While warm water fuels hurricanes, wind shear can weaken them. Wind shear refers to the difference in wind speed and direction at different heights within a hurricane. Strong wind shear can tear a tropical storm apart and keep it from strengthening.
In El Niño years like 2023, wind shear in the Atlantic basin is usually strong. However, in the case of Idalia, the wind shear is not expected to be strong enough to withstand the extreme heat. On Monday morning, wind shear was around 16 knots, and by Wednesday morning, it is forecast to reach around 21 knots. While this is moderately strong winds, it is not enough to tear the hurricane apart. As a result, Idalia is expected to intensify rapidly due to high ocean temperatures.
Haiyan Jiang, a hurricanologist at Florida International University, explains, “The conflicting forces of unusually high ocean temperatures and wind shear have made this hurricane season and individual storms difficult to predict. Extreme heat in the Gulf of Mexico provides enough fuel to strengthen Idalia, while wind shear is not strong enough to counteract it.”
According to NOAA Coast Watch, Idalia’s projected path is through some of the deepest heat reservoirs in the Caribbean and Gulf of Mexico. Oceanic heat content, which measures the depth of warm water spread, shows that Idalia will encounter warm water from the sea surface to an isotherm of 26 degrees Celsius (78.8 degrees Fahrenheit).