The Gulf of Mexico – the land-fringed head of hurricane alley along whose edge some 16 million Americans live – is observing its warmest start to a hurricane season (and year) since satellite records began in 1981.
The exceptional marine heat is driving up nighttime lows from South Florida to Texas and contributing to oppressive summer heat indices, including a record 31 consecutive days of heat indices over 100 degrees Fahrenheit in Miami. The environmental impacts of such an intense marine heatwave are far-reaching – from extreme coral bleaching stressing important reef ecosystems to decreasing oxygen levels for marine life, leading to large hypoxic episodes, dead zones and fish kills.
What influence could the record warm Gulf of Mexico have on the hurricane season ahead?
Sea surface temperatures are an important factor for hurricane development – warm waters, especially those above 80 degrees Fahrenheit, drive the hurricane heat engine, transferring copious storm energy to the atmosphere through a vicious feedback loop of high humidity and organized thunderstorms. When wind speed and direction don’t change much from the sea surface to around 40,000 feet – that is, when vertical wind shear is light – hurricane can thrive and quickly strengthen.
While sea surface temperatures in the Gulf are not a good predictor for overall seasonal hurricane activity – the main development region and eastern Atlantic tell us more about upcoming seasons – they are locally important for coastal impacts when hurricanes form.
Studies have shown that only a small tick up – about a degree Fahrenheit increase – in peak hurricane sea surface temperatures are responsible for a 40% increase in hurricane activity and frequency.
Rising sea surface temperatures could double the number of Category 4 and 5 hurricanes by the end of this century, most notably in the western Atlantic and parts of the Gulf of Mexico.
Additionally, as water temperatures warm from 80 to 85 degrees Fahrenheit, hurricane rainfall, one of the deadliest calling cards of tropical cyclones, increases by a factor of 5. Once sea surface temperatures surpass 83 or 84 degrees Fahrenheit, fully-formed hurricanes often undergo periods of rapid intensification, especially when wind shear is light.
The warming of the Gulf has increased especially since middle June, soaring to weekly highs above those seen in 2020, the previous recordholder. The record warmth is also measured at several nearby coastal tide stations – including Key West and Vaca Key in the Florida Keys, whose high-fidelity records date back to the 1990s.
A much weaker-than-average subtropical high pressure over the Atlantic has reduced the cooling effect of typically brisk trade winds across the Gulf this summer but the biggest underlying culprit to increasing Gulf temperatures is climate change.
Nine of the top 10 warmest starts to the year (through June) across the Gulf of Mexico have occurred since 2012. A study published this past February found the Gulf is warming at a rate twice that of global oceans.
The warmth is undoubtedly compounding damage potential from hurricanes along the Gulf Coast as coastal population continues to increase and coastal sea levels accelerate.
For today, the Gulf of Mexico and tropical Atlantic writ large are absent any storms and will be at least through the week. The only exception can be found in the subtropical North Atlantic, where an area of low pressure has a medium chance at briefly becoming a tropical or subtropical depression in the next few days.
The system will remain over the open ocean and poses no threat to land.