TC Zelia’s Power: More Energy Than Australia Uses in a Year!

February 16, 2025

Tropical Cyclone Zelia located off the Pilbara Coastline on February 13, 2025.

Tropical Cyclone Zelia didn't just bring howling winds and towering waves—it literally changed the ocean itself. In just a few days, Zelia drained more energy from the ocean than Australia uses in a year across all sectors.

Tropical Cyclones: Nature’s Heat Engine

Tropical cyclones are nature’s most powerful heat engines—they thrive on warm ocean waters, converting stored heat into destructive winds and torrential rain. The warmer the ocean, the stronger the tropical cyclone can become, as more heat is available to fuel the storm’s intensification.

Before Zelia, sea surface temperatures (SSTs) off the Pilbara coastline were hovering around 31-32°C—exceptionally warm conditions, even for northern Australia. If the setup had been slightly more favourable, Zelia could have intensified even further into a high-end Category 5 system. But even as a low-end category 5, Zelia was so powerful that it cooled more than 100,000km² of ocean by 1-2°C.

Before and after SSTs off the NW WA coastline showing the 31-32C SSTs having been completely eroded from the region due to TC Zelia. Source: BoM

This may not sound like much, but when you consider the depth of water affected (even just the top 10m of the ocean), this cooling equates to a staggering 5,000 to 10,000 petajoules of energy. For comparison, in 2022-23, Australia used 5,882 petajoules of energy (source: https://www.energy.gov.au/energy-data/australian-energy-statistics/energy-consumption).

How Did Zelia Cool the Ocean?

There are two main ways that a tropical cyclone cools the ocean:

1️⃣ Upwelling: The extreme winds churn the ocean surface, bringing cooler, deeper waters up to the surface. This is why some regions experience a sudden drop in SSTs after a strong tropical cyclone. Hi-res satellite imagery shows the discolouration in the water from the aftermath of Zelia off the coastline.

2️⃣ Energy Conversion: As warm ocean water evaporates, it fuels the tropical cyclone—this process converts heat energy into mechanical energy (wind and waves) and latent heat release (which sustains deep convection). The stronger the tropical cyclone, the more heat it pulls from the ocean.

In other words, Zelia didn’t just pass over the ocean—it actively drained it of energy.

The discoloration of the water off the coastline shows how the ocean has been disturbed off the coastline. Flooding (shown by the brown water) near De Grey can also be seen.

A Temporary Cooling Effect

Despite Zelia’s intense cooling, the ocean won’t stay cooler for long. Thanks to persistent warm currents and solar heating, SSTs will gradually warm in the coming weeks. However, in the short term, this cooling effect can limit further tropical cyclone development in the same area—something often observed after major tropical cyclones.

The World's Warming Oceans May Sustain Stronger Tropical Cyclones

The interaction between tropical cyclones and ocean temperatures is crucial for forecasting and climate trends. While Zelia’s energy drain was immense, rising global ocean temperatures mean that future tropical cyclones may have even more heat to work with, potentially leading to more intense systems.

Warm oceans have become an increasing feature in recent years which may fuel stronger tropical cyclones.

A Near Miss for Port Hedland

Fortunately, Zelia crossed over a remote section of the Australian coastline with the eye crossing the coastline 50km to the northeast of Port Hedland. Even 50km away, Port Hedland still experienced wind gusts of 120km/h - a reminder to how concentrated winds are within a tropical cyclone. The impacts on Port Hedland were more akin to a low-end category 2 system - so residents should not be complacent should a direct hit from a category 4 or 5 hit at some point in the future.

The anatomy of a tropical cyclone - even an intense system can have a very small radius of very destructive winds.

Flooding and rainfall were the main impacts. Marble Bar recorded a total of 203mm in 24 hours - nearly double the previous wettest February day on record. Over a five-day period, Marble Bar recorded 385mm of rainfall, exceeding its annual average (358mm) and securing its wettest February on record.

Major flooding occurred around Marble Bar due to the record rainfall.

Western Pacific Next to Watch for Tropical Cyclone Development.

As the MJO finally marches into the Pacific Ocean, we'll be more likely to see tropical cyclone development across the western Pacific during the second half of February. However its far too early to speculate whether any of these may drift close enough to generate any impacts to Queensland.

The MJO phase will favour the western Pacific for a period and may result in a higher chance of tropical cyclone development here during the last 10-12 days of February. Source: BoM.

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