Earth’s Nonstop Cyclone Season Shifts South Toward FijiBrian K. Sullivan
Some tropical storm watchers looking at the calendar might think there will be few things to chase as both the Atlantic and Pacific seasons enter their last month on Nov. 1.
They’d be wrong.
The Earth never stops producing tropical cyclones, the scientific name for the class of systems that includes tropical storms, typhoons and hurricanes.
The western Pacific, for instance, has no set typhoon season because storms can erupt there pretty much any time of year. The same is true for any of the world’s oceans, just not as likely. There are actually two peaks to the season in the Bay of Bengal, one from April through June and the other from September through December.
“These periods flank the monsoon season,” said Gerry Bell, a hurricane research specialist at the U.S. Climate Prediction Center in College Park, Maryland.
Wind shear, or conflicting wind patterns, set up by the monsoon tends to shut down storm formation in the Indian Ocean. Bell said larger, continental weather systems tend to trump smaller, localized ones such as hurricanes, which is why Brazil, with its large area of wind shear off the coast, almost never gets hit.
While the South Atlantic may be out, that’s not the case across the entire Southern Hemisphere as spring and summer arrive.
The Australian tropical cyclone season begins Nov. 1 and has an average of 11 storms, one fewer than the Atlantic hurricane season. This year, forecasters are calling for an average to below-average season, according to the Australian Bureau of Meteorology.
The possibility of an El Nino developing in the Pacific north of Australia can keep the number of storms lower than average there, just as it does in the Atlantic. The sea warming phenomenon also means that the first cyclone to strike land usually comes in January, rather than December, when the surface temperatures in the Pacific are nearer to neutral, the bureau said.
Australian storms get alternating male and female names and are classified on a five-step scale. While not the same as the Saffir-Simpson scale used in the U.S., in the Australian system a Category 5 storm is still the strongest.
To the east of Australia lies the Fiji Meteorological Service’s Regional Specialized Meteorological Centre in Nadi, which has responsibility for a host of South Pacific islands including New Caledonia, Fiji and Samoa. It also issues seasonal forecasts, and, like Australia, its season runs from Nov. 1 to April 30.
A seasonal outlook for that region hasn’t been posted on its website yet. However, through 2011-12, during El Nino years, an average of 8.7 storms have occurred since 1969-70, while 6.6 happen in neutral years and 6.5 if there’s a La Nina ocean cooling.
As the chances of a storm dwindle through much of the Northern Hemisphere, things will only be getting started in the South. Cyclone-watching never stops.