Analysing the atmospheric-oceanic conditions driving the sustained long track and intensity of Tropical Cyclone Freddy

Abstract

During February–March 2023, the record-breaking tropical cyclone (TC) Freddy caused widespread flooding and damages across southeastern Africa. While <5 % of TCs make landfall into southern Africa, TC Freddy made landfall twice and is the only TC in the past two decades that has tracked over 8000 km across the entire southern Indian Ocean. To understand why TC Freddy was so unique, this study investigated the evolution, track and atmospheric-oceanic mechanisms driving TC Freddy using the ERA5, CFSv2, OSTIA, NCEP-NCAR datasets and track data from various sources. It was found that SSTs were >27 °C during TC Freddy’s lifetime, while TC Dingani and a split Mascarene High played a role in steering TC Freddy across the southern Indian Ocean. Leading up to the development of TC Freddy, conditions were favourable for TC genesis, as indicated by the levels of the Genesis Potential Parameter (GPP) and its modified version (GPPI), the tropical cyclone heat potential levels, and elevated SSTs. Ridging subtropical anticyclones and the Mascarene High alongside favourable steering flow and GPP (and GPPI) conditions resulted in Freddy’s double landfall in Mozambique. In assessing the tracks, it was found that there are discrepancies in the track of the commonly used IBTrACS when compared to ERA5 and RSMC tracks, which has implications for impact studies due to the underestimation of landfall considerations. This study reveals the unique characteristics and atmospheric-oceanic mechanisms driving TC Freddy, emphasising the importance of accurate representation of favourable conditions and track data for enhancing TC forecasting and impact assessments.