Late-season storm defies strong El Niño as unusually warm Gulf waters fuel its development.
Isaias hurricane winds force reached 120.701 KM/H.
Strong El Niño conditions had suppressed Atlantic hurricane activity for much of the season.
Exceptionally warm Gulf waters and weaker wind shear helped Isaias strengthen, while climate change may have contributed to the unusually warm ocean conditions.
Hurricane Isaias is getting stronger over the Gulf of Mexico as it heads toward the U.S. Gulf Coast.
The storm had maximum sustained winds of about 75 mph (120 km/h) on Thursday and was located roughly 715 kilometers south-southwest of the mouth of the Mississippi River, according to the U.S. National Hurricane Center. Forecasters expected Isaias to strengthen further as it approached the northern Gulf Coast.
The storm's development is particularly notable because the 2026 Atlantic hurricane season has been unusually quiet. A powerful El Niño has been one of the major factors suppressing hurricane formation by increasing wind shear over parts of the Atlantic, making it harder for tropical systems to organize.
However, conditions in the Gulf of Mexico were different.
Unusually warm Gulf waters and weaker wind shear created a more favorable environment for Isaias. The Gulf waters in the area were several degrees warmer than average for this time of year, providing the heat and moisture needed to strengthen the developing storm.
Another atmospheric factor was the Madden-Julian Oscillation, a naturally occurring pattern of tropical thunderstorms and atmospheric circulation that can influence where conditions become favorable for tropical cyclone development. Scientists said the combination of the MJO, warm Gulf waters and weaker wind shear helped create the window in which Isaias could develop despite El Niño.
El Niño did not prevent Isaias
The formation of Isaias does not mean El Niño stopped affecting the Atlantic. Instead, it demonstrates how large-scale climate patterns can create different conditions in different parts of the same basin.
Strong El Niño conditions generally suppress Atlantic hurricanes, and NOAA had forecast that the unusually strong 2026 El Niño would lead to below-average Atlantic hurricane activity. At the same time, NOAA noted that hurricanes developing during El Niño years can be shifted toward the Gulf Coast and subtropical regions.
Isaias therefore developed in an area where local conditions were temporarily more favorable than the broader Atlantic environment.
What role does global warming play?
Scientists also point to human-caused climate change as a factor in the exceptionally warm Gulf waters.
Warmer oceans can provide more energy for tropical cyclones and allow the atmosphere to hold more moisture, increasing the potential for heavier rainfall. A Climate Central analysis cited by public radio outlet WUSF found that global warming had made the unusually warm waters around Isaias far more likely.
That does not mean climate change directly caused Isaias. Tropical cyclones result from a combination of ocean temperatures, atmospheric circulation, wind shear, moisture and natural climate patterns.
In Isaias's case, the interaction between El Niño, unusually warm Gulf waters, weak wind shear and other atmospheric conditions is central to understanding why the storm formed so late in the season.
Threat to the Gulf Coast
Isaias is expected to bring hurricane-force winds, dangerous storm surge and heavy rainfall to parts of the northern Gulf Coast. Forecasts called for roughly 76.2 mm of rain in parts of Florida, Alabama and Mississippi, with locally higher amounts possible.
Authorities have declared emergencies in affected areas, while some communities have ordered evacuations and closed schools as the storm approaches. Officials are also warning of possible flooding and prolonged power outages.
Oil production disrupted
The hurricane is also threatening the Gulf's important energy industry.
Oil and gas companies have evacuated workers from offshore facilities and reduced production ahead of the storm. About 25% of Gulf oil production and 16% of natural-gas production had been temporarily shut in as of Wednesday, according to U.S. government figures cited by Reuters.
The disruption could add pressure to energy markets at a time when oil prices are already elevated.
A historically late hurricane
Isaias formed exceptionally late in the season. The Atlantic's first hurricane had not formed this late since October 8, 1905, making Isaias notable in the historical record.
The storm illustrates how hurricane seasons cannot be judged solely by how quiet they appear early on. Even during a season suppressed by a strong El Niño, a combination of warm ocean water and favorable atmospheric conditions can allow a dangerous hurricane to develop.
