Interactions between Hurricane Catarina (2004) and warm core rings in the South Atlantic Ocean

The unexpected evolution of the first recorded South Atlantic Hurricane Catarina over waters with homogeneous sea surface temperatures (SST) of 24 degrees C in March 2004 was a challenge to the weather forecast community. This work concentrates on a thorough data-driven comparative analysis to make reliable diagnostics of the role of the ocean in the genesis and evolution of Catarina. We used several high-resolution multisatellite-derived products, including three microwave-based SST data sets, multisatellite collinear data of sea surface height (SSH) anomalies, significant wave heights and wind speeds, four QuikSCAT ocean surface wind vector products (including the 12.5 km resolution swath data), daily fields of absolute objectively analyzed SSH and corresponding geostrophic currents, and Argo floats. The synergic use of these data sets showed that Catarina interacted strongly with four warm core rings (WCRs), forcing upwelling of isotherms and mixed layer waters. These interactions minimized the known negative SST feedback, as attested by the SST differences being less than 1.2 degrees C. Although the SST in the region was around 24 degrees C, below the Palmen threshold, the surface air temperatures were 14 degrees C which still furnished a large air-sea temperature gradient capable of extracting large enthalpy fluxes from the WCRs influenced by Ekman pumping. It is shown here that Catarina achieved category 1 over the ocean on 26 March with its maximum intensity of 34 m/s seen in the 12.5 km swath winds.