For the second year in a row, it is remarkably quiet in the Atlantic Ocean. Normally, on September 10, the peak of the hurricane season occurs, but this year it is very calm in the Atlantic Ocean, with no hurricanes in sight. What is going on and what does this mean for the rest of the hurricane season?
Why is it so quiet?
The calm is mainly caused by strong winds at high altitudes. In meteorological terms, we call this wind shear: the difference in wind speed between the surface and high altitudes. Hurricanes can generally only form in an environment with little wind shear. When there is more wind shear, the hurricane gets blown apart.
That there is so much wind shear now is remarkable; usually, there is little wind shear over the Atlantic Ocean during this period. The red areas in Figure 1 are areas where there is currently more wind shear than normal; the circled areas are areas where hurricanes could form during this period of the hurricane season. But what we see is that precisely in those areas there is now a lot of wind shear, making it difficult for storms to develop into hurricanes.
In addition to wind shear, dry air also makes it difficult for storms to develop into hurricanes. Hurricanes need moist, warm air to form and grow, as they derive their energy from this air. However, when dry air, for example from the Sahara, enters the hurricane, it can cause the hurricane to effectively suffocate. The hurricane is then cut off from the supply of warm, moist air and weakens, sometimes to the point where the hurricane completely disappears. We saw this happen last weekend, when a group of thunderstorms escaped the wind shear and tried to develop into a hurricane, but then encountered a lot of dry Sahara air and thus fizzled out.