Tropical Cyclone Zelia Forecast: Cat 1 to Cat 5 Monster in Just 36 Hours

February 13, 2025

At 3am WST on Wednesday, Tropical Cyclone Zelia was officially named by the Bureau of Meteorology. However, within just 24 hours, Zelia had already intensified to a high-end Category 3 with wind gusts reaching 220km/h. By 2pm WST this afternoon, it is forecast to reach Category 5 strength, with wind gusts exceeding 280km/h.

Current indications forecast that Zelia will cross the coastline near Port Hedland, though expect some variation as Zelia will be slow moving for the next 24 hours.

Why is Zelia intensifying so quickly?

The rapid intensification is being fueled by a combination of factors. Sea surface temperatures (SSTs) are extremely warm, sitting at 31-32°C, more than sufficient to sustain an extremely powerful tropical cyclone. However, high-end tropical cyclones require more than just warm waters to intensify rapidly.

SSTs are extremely warm, exceeding 32C in small areas off the WA coastline. Source: BoM

A passing upper trough to the south had initially been exerting wind shear over the system, which can disrupt a cyclone’s delicate structure. However, in the past 12 hours, upper-level winds have weakened to a more favourable level, allowing for broader outflow and divergence in the upper atmosphere. This divergence—winds spreading outward from the cyclone’s center—acts like a giant exhaust fan, enabling the system to pull in humid air at the surface, channel it through the storm, and expel it high into the atmosphere. This process allows further intensification to occur.

CIMISS wind shear. Yesterday, Zelia was located in a zone of stronger shear (red winds of 20-30 knots), today Zelia has entered a region of lower shear (10-20 knots). Green areas indicated regions favourable for tropical cyclone development of intensification. Red areas indicate areas unfavourable for tropical cyclones.

Additionally, Zelia has been moving more slowly than initially forecast, allowing it to linger over warm waters for longer, further aiding its rapid intensification.

Tropical Cyclone Zelia showing winds exceeding 150 knots at 850mb. Source: HAFS-A TC modelling from MetCentre.

Path Uncertainty: Why Tracking Zelia is Tricky

Tropical cyclones that move slowly are often harder to predict because the systems steering them are relatively weak. Even small shifts in the surrounding atmospheric patterns can lead to changes in both path and timing, which explains the large cone of uncertainty in the BoM’s forecast.

The cone of uncertainty is very broad - this means the forecast of the system could still occur as far west as Onslow or Exmouth (albeit a less likely outcome). Source: BoM

Zelia is currently being wedged between three competing steering influences:

An upper high to the east—pushing the system southwest

An upper high to the west—nudging it northeast

An upper trough to the south—driving it southeast

300mb winds showing the multiple steering influences and "pushes" on Zelia. However the system to the west is expected to weaken and this should allow the influences pushing it more southwards to dominate.

Eventually, the western influence is expected to weaken, allowing Zelia to take a more southerly track by tomorrow. While the current forecast takes the system over or very close to Port Hedland, all communities along the Pilbara coastline should be monitoring this system very closely given the large uncertainty around the path and timing of this system.

Tropical Cyclone Zelia is likely to generate torrential rainfall and flooding across northwestern Western Australia. Source: EC accumulated rainfall from MetCentre.

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