Weak Ocean Temperature Differences Can Make Tropical Cyclones Far Stronger, Study Finds

A new study suggests that weak temperature differences across small patches of the ocean surface can make tropical cyclones significantly more intense, offering a potential tool for better storm warning systems. Published in the Proceedings of the National Academy of Sciences, the study focuses on sea-surface temperature gradients — horizontal differences in ocean surface temperature that can exist over distances as short as 1 kilometer to tens of kilometers.

Tropical cyclones draw their power from warm ocean water, but a storm's winds normally churn up colder water from below, cooling the sea surface and weakening the storm. To see how small-scale surface temperature gradients affect this process, the researchers combined global tropical-cyclone track records from 2003 to 2022 with high-resolution satellite sea-surface temperature maps, measuring the gradients in the days before each storm arrived.

Cyclones that crossed weak pre-storm temperature gradients caused less ocean cooling and grew about 40% stronger, on average, than storms crossing the strongest gradients. The effect was more pronounced for storms undergoing rapid intensification: about 60% of these cyclones were associated with below-average pre-storm gradients, a proportion that rose to about 70% for Category 4 storms.

Tropical cyclones cause more than 10,000 deaths and $26 billion in economic damage worldwide each year, according to the study. The authors found that sea-surface temperature gradients have weakened by about 10% per decade since 1993 across cyclone-active regions, which may be increasing storm intensity. Current storm-ocean models generally cannot resolve these small-scale features, so the authors say more direct observations and high-resolution simulations are needed to translate the finding into better forecasts.