Tropical cyclones in the Mozambique Channel: relationships with atmospheric teleconnections

Tropical cyclones (TCs) that form in the Mozambique Channel are relatively close to land, yet few studies have specifically examined these TCs. This study analyzes formation locations and trajectories for these storms during 1980-2010 when TC observations are known to be more reliable relative to earlier periods. A Geographic Information System (GIS) is used to plot formation location, calculate storm heading and track shape using TC position data from IBTrACS, and to extract environmental conditions from NCEP/NCAR reanalysis data including vertical wind shear, sea surface temperatures (SSTs), and velocity potential. Nonparametric statistical tests determine the strength and direction of the relationships between these conditions, TC attributes, and five atmospheric teleconnections known to influence circulation patterns in the greater Southwest Indian Ocean: the El Niņo Southern Oscillation (ENSO), Indian Ocean Subtropical Dipole (IOSD), Madden-Julian Oscillation (MJO), Quasi-Biennial Oscillation (QBO), and Southern Annular Mode (SAM). Results show that 40 TCs formed in the channel during the study period and 21 made landfall over Madagascar or Mozambique. More TCs formed in the equatorward (poleward) sections of the channel when the IOSD and SAM were negative (positive). Trajectories of TCs forming north of 18° S tended to be curved and initially move south or southwest while experiencing easterly vertical wind shear and higher SSTs while those south of 18° S moved fairly straight from west to east over lower SSTs and strong westerly vertical wind shear. Landfall tended to occur over Madagascar when the MJO was in position to enhance cyclogenesis over the channel, while landfall over Mozambique tended to occur when higher geopotential heights at 500 hPa were present on the day of formation. The QBO and ENSO did not exhibit statistically significant relationships with formation frequency, location, or track shape. These results suggest that further research into linkages between teleconnections, environmental conditions, and TC attributes should be explored for TCs forming in the Mozambique Channel as they may differ when compared to those for TCs that form in the greater Southwest Indian Ocean.