It is hurricane season. The official hurricane season for the northern hemisphere is the beginning of June to the end of November. This morning Tropical Storm Michael in the Gulf of Mexico was promoted to the status of hurricane. As I sit here at the Richmond Hill Hatchery just south of Savannah I am checking on the status of Hurricane Michael to determine when I will begin my journey back home to north of Atlanta.
Hurricanes begin as tropical storms over warm moist waters around the Intertropical Convergence Zone (ITCZ). Hurricanes are heat engines. As Hurricane Michael enters the Gulf of Mexico it will strengthen as it glides across the warm waters of the Gulf.
The ITCZ (pronounced “itch”) is also known as the Equatorial Convergence Zone and it shifts north and south seasonally following the Sun and warmer ocean temperatures. Due to these shifts with the tilt of the Earth’ axis the tropics have wet and dry seasons. The ITCZ is a belt of converging trade winds and rising air. This rising air results in frequent thunderstorms and heavy rainfall.
The heat capacity of the oceans is greater than air over land so in the northern hemisphere the migration of the ITCZ is more prominent over land. Over the oceans, the ITCZ is better defined and the seasonal cycle is subtler because the converging trade winds are constrained by the distribution of ocean temperatures.