August 4, 2021

Cyclone Seroja: Australia is preparing for the worst

Cyclones Odette and Seroja near the Australian coast. Photo credit: MODIS Land Rapid Response Team, NASA GSFC


The destructive system, which in particular killed more than 130 people in Indonesia and caused much damage, gained in intensity just before its arrival in Australia. Cyclone Seroja, which was previously Category 1, has moved to Category 3 on the Beaufort scale. This is the equivalent of a hurricane of force 1 on the Saffir-Simpson scale, used in North America.

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Winds of up to 165 km / h are to be expected, along with heavy rain and flash flooding, according to the Australian Government’s Office of Meteorology. Moreover, the town of Kalbarri recorded gusts of 170 km / h around 7 p.m. local time, and the west of the country has so far received more than 111 mm of rain.

Local authorities have said they expect extensive damage all along the west coast as the buildings on Seroja Road were not built to withstand such strong winds. Normally, the trajectory of cyclones in this part of the world is further north of the country.

Fujiwhara effect

This gain in strength can be explained in particular by the Fujiwhara effect. This is a rare weather phenomenon that occurs when two hurricanes or cyclones, swirling in the same direction, pass close to each other. The two systems then begin to gravitate toward each other, which can either change their respective trajectories, increase their intensity, or cause them to merge. In this case, it was an encounter with the smaller-amplitude cyclone named Odette that gave rise to this phenomenon last Friday. Without merging, however, Odette allowed Seroja to gain in intensity.

Loss of intensity to come

While for now residents of areas between Carnarvon and Perth expect the worst, Seroja is expected to lose intensity as it rushes inland, according to the Australian Government’s Meteorological Office. The organization predicts that the cyclone should subside and return to Category 1 by Monday morning.


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