By some measures, it has been the busiest South Indian Ocean hurricane season on record. In terms of damage and major hurricanes, it appears to have been the worst in modern history.
Hurricane scientists define the South Indian Ocean basin as the part of the ocean south of the equator, and west of 135 degrees longitude—this encompasses an area from Africa to the western part of Australia.
The “cyclone” season for the South Indian Ocean generally runs from about September through April, but for record-keeping purposes it runs from July 1 of a given year to June 30 the next.
The 2018-2019 season, which began on July 1, has recorded 17 storms, according to statistics maintained by University of Colorado hurricane scientist Phil Klotzbach, and based on data from the Joint Typhoon Warning Center. While that by itself is not a record, as the basin has had as many as 22 storms dating back to 1980, the storms this season have been especially strong.
For this season, the South Indian Ocean has recorded 10 “very intense cyclones,” the equivalent of a major hurricane in the Atlantic Ocean, or a Category 3 or stronger storm on the Saffir-Simpson scale. According to Klotzbach, the previous record for major hurricanes in the Indian Ocean is eight, which occurred during the 2006-2007 season. Records prior to 1979 for this area are generally unreliable, due primarily to the lack of full satellite coverage until that time.
The most notable storm of this season has been Cyclone Idai, which followed a remarkable track that brought it onshore the African nation of Mozambique in March, where it meandered for five days, before reemerging into the waters between Mozambique and Madagascar, rapidly strengthening, and making a second landfall in Mozambique. Idai is estimated to have killed more than 1,000 people, and it caused about $1 billion in damage.
Idai is the costliest cyclone on record in the South Indian Ocean and deadliest single storm of the modern era for that region.
As active as the South Indian Ocean has been, Klotzbach said it historically does not have a meaningful correlation with North Atlantic hurricane activity. “I don’t think that it has too much bearing on the upcoming Atlantic hurricane season,” Klotzbach told Ars.
Klotzbach’s Tropical Cyclone Project released its initial forecast for the 2019 Atlantic season earlier this month, calling for “slightly below normal” levels of activity this year. This was due, in part, to the likely persistence of an El Niño event (which tends to increase wind shear over the Atlantic), and moderately cooler sea surface temperatures averaged across the tropical Atlantic.