Explosive cyclogenesis is underway over the eastern Indian Ocean, where a rapidly deepening low pressure system is setting parts of southwest Western Australia up for a wild weekend of damaging to destructive winds, heavy rain, thunderstorms and dangerous seas. Models show the low’s central pressure plunging by an average of about 25 hPa in 24 hours, a dramatic pressure fall that can turn an ordinary low into a powerful “bombing low”. 

A low becomes a “bombing low” through a process called explosive cyclogenesis, when its central pressure falls unusually quickly in 24 hours. This rapid pressure drop usually happens when powerful atmospheric ingredients line up. On Sunday morning, model guidance shows an intense jet stream, roughly 9 to 10 km above the ground, with winds near 300-310 km/h over southwest WA (image 1). That is an exceptionally strong upper-level jet, well above the 180 km/h benchmark that EUMeTrain cites as being associated with developing explosive cyclogenesis, based on Lim and Simmonds (2002). This powerful jet helps air evacuate from above the low, allowing surface pressure to fall more rapidly. 

Image 1. ECMWF HRES 300 hPa jet stream (roughly 9-10kms above the ground) forecast for Sunday morning, showing an intense upper-level jet over southwest WA with winds near 300-310 km/h.

Abnormally warm waters off parts of the WA coast are also feeding moisture and energy into the system (image 2), while a pool of cold air or cut off low in the upper atmosphere is helping create a sharp contrast between warm, moisture laden air below and much colder air above (image 3).

Image 2. Daily sea surface temperature anomaly analysis for Thu 28 May 2026, showing warmer-than-average waters off parts of the WA coast, including anomalies of around +1 to +2°C in areas west and southwest of the state. Source: Bureau of Meteorology. 

Image 3. ECMWF HRES 500 hPa temperature and geopotential height forecast for Sunday morning, showing a pool of colder air about 5 to 6 km above the ground west of southwest WA. 

That contrast makes the atmosphere more unstable and helps the low deepen rapidly. As the pressure falls, surrounding air rushes in more aggressively, isobars tighten, and winds ramp up quickly (image 4).

Image 4. ACCESS-G3 wind gust forecast for Sunday afternoon.

To classify explosive cyclogenesis, meteorologists look at how much the central pressure falls in 24 hours, but they do not use the same pressure-drop threshold everywhere on Earth. The threshold changes with latitude because the Earth’s rotation affects how air moves around low pressure systems. At higher latitudes, the rotational effect is stronger, so the pressure fall needs to be larger. At lower latitudes, that rotational effect is weaker, so a smaller pressure fall can still be enough to show that a low is intensifying explosively.

According to Lim and Simmonds (2002), this latitude-adjusted threshold is about 12 hPa in 24 hours at 25S and 18 hPa in 24 hours at 40S. This low is expected to move between roughly 35S and 37S during the next 24 hours, placing its threshold near 16 to 17 hPa in 24 hours. With models showing an average fall near 25 hPa in 24 hours, as shown in the graph below, this low is expected to deepen well beyond the explosive cyclogenesis threshold.

Image 5. Modelled 24-hour central pressure fall for the developing low. Models show an average fall near 25 hPa in 24 hours. 

For southwest WA, this means a rapidly worsening spell of weather through the weekend, with damaging to destructive winds, heavy rain, thunderstorms, large surf and hazardous marine conditions likely before the low shifts away early next week. Residents should secure loose outdoor items, avoid exposed beaches and coastal roads, never drive through floodwater, and keep up to date with the latest warnings.