Ocean Heat Content Trends and Their Implications for Tropical Cyclone Intensification

Abstract

Rapid intensification, an increase in maximum sustained wind speed of at least 30 kt in 24 hours, remains one of
the least well forecast aspects of tropical cyclone behaviour, and the depth of warm water available to a storm, not
just sea surface temperature, is increasingly implicated as a control on which storms undergo it. We combined
2005-2022 Argo float temperature profiles, quality-controlled hydrographic casts, and two ocean reanalysis
products (ORAS5 and GLORYS12) to reconstruct upper-ocean heat content and tropical cyclone heat potential
(TCHP) across four basins, then matched these fields along the tracks of 641 tropical cyclones of tropical storm
intensity or greater drawn from IBTrACS, restricting the intensification analysis to the 24 hours following each
along-track ocean sampling point. Basin-mean 0-700 m ocean heat content rose over the study period at rates
ranging from 1.9 GJ m-2 decade-1 in the eastern North Pacific to 4.6 GJ m-2 decade-1 in the western North Pacific
warm pool, with the North Atlantic main development region and the Gulf of Mexico-Caribbean corridor showing
intermediate trends of 2.7 and 3.4 GJ m-2 decade-1 respectively. Storms that crossed a warm-core eddy or Loop
Current filament with TCHP exceeding 80 kJ cm-2 intensified at a mean rate of 11.4 kt per 24 h, versus 5.8 kt per 24
h for storms over ambient water of comparable sea surface temperature but without an eddy encounter, and the
probability of a rapid intensification onset was roughly three times higher in the eddy-encounter subset (29 percent
versus 10 percent). The relationship between TCHP anomaly and 24-hour intensification rate was statistically
significant but explained only a modest share of the variance (Figure 1), consistent with intensification remaining
jointly controlled by vertical wind shear, mid-level humidity, and storm-induced ocean cooling feedbacks that this
heat-content-centred analysis did not resolve. Basin comparisons further indicated that the western North Pacific,
where warm-core eddies are more numerous and TCHP anomalies larger, showed a stronger eddy-related
intensification signal than the North Atlantic. These results support incorporating basin-resolved, eddy-aware ocean
heat content fields, rather than sea surface temperature alone, into operational rapid intensification guidance, while
underscoring that ocean thermal structure is a necessary but not sufficient predictor of which storms will intensify
rapidly.