The thunderstorm that arrives like clockwork at 3pm every day

The northern wet season has officially commenced, coinciding with the annual arrival of the Top End's largest resident.

Looking north from Darwin, a marvel of meteorology, one of the largest storm clouds on the planet towers over the Tiwi Islands from about 3pm every day.

It is the world's only individually named thunderstorm, with locals calling it Hector.

A giant storm as old as time

Hector was labelled by World War II pilots, who used its dependable location as a navigation beacon when travelling between Darwin and Papua New Guinea.

But you do not need a plane to spot Hector. The thundercloud is clearly visible from Darwin, and that is because he is no ordinary storm.

While the storm got the name Hector 80-odd years ago, the Indigenous communities of the Tiwi Islands were well aware of its occurrence with the traditional calendar tracking the changes in the land and sky across three major and 13 minor seasons.

The two major seasons which overlap with Hector are Tiyari and Jamutakari, which run from September to February.

During Jamutakari, pakitiringa (rain) falls consistently every day and the swamps, creeks and rivers are full. There is much pumurali (lightning) and thunder with the rain.

One of the minor seasons also references the arrival of a daily storm. Pumwanyingari is the season of thunder when humidity increases and clouds develop every afternoon.

Hector is a colossus, rising vertically up to 20 kilometres in altitude.

Hector is so tall he soars right through the troposphere, the layer of the atmosphere where weather occurs, and punches into the lower stratosphere, a hostile environment which flattens out his head.

Containing millions of tonnes of water, Hector is also known as Hector the Convector, since he transfers such a massive amount of heat and moisture from the warm tropical surface high into the atmosphere.

He can easily drop 50 millimetres of rain in a couple of hours and contributes to the Tiwi Islands being the wettest part of the Northern Territory with up to 2,000mm annually.

How Hector overcomes chaos theory

Forecasting the exact location and timing of an individual thunderstorm before it forms is one of the greatest challenges in meteorology; just ask Doc Brown from Back to the Future.

In fact, it is nearly impossible since the three key ingredients for a storm rarely occur simultaneously at the same time and place each day.

So how does Hector overcome the chaotic and inherently unpredictable nature of weather?

Hector's existence is the result of the unique geography of the Tiwi Islands.

The first ingredient for a storm is moisture, and since the Tiwi Islands are surrounded by warm tropical seas, water vapour is abundant.

Ingredient two is instability, which utilises the property of physics that warm air rises.

The largest of the Tiwis is Melville Island, the second largest in Australia after Tasmania, with dimensions of roughly 50 by 100km.

What is critical is that Melville Island is small enough that the centre is still inundated by moist maritime air, but it is large enough that the middle sees peak daytime temperatures up to 5 degrees Celsius warmer than the coastline.

The result is sufficient heat and humidity at the surface to ensure a parcel of air moving vertically upwards will remain warmer than the surrounding air and therefore keep on rising to form a towering cumulonimbus storm cloud.

The third and final ingredient, and often the missing link that prevents reliable storms elsewhere, is a trigger.

The trigger is the mechanism required to launch air from the surface and overcome gravity, and heat alone will not do the job, otherwise the entire layer of surface air over the sunlit side of the planet would simultaneously rise.

What you need is another force to initiate uplift, which could be a mountain range, a cold front, or perhaps converging winds.

Again, the Tiwi Islands has Goldilocks geography. Since the centre is warmer, and warm air is light, a sea breeze develops each day that carries in cooler, denser air from the ocean.

But unlike a mainland sea breeze which just blows in one direction from the ocean to the land, an island's sea breeze draws in air from all directions.

Eventually, all that inward-blowing wind meets in the middle where it is then forced to rise vertically (since it cannot blow into the ground), a process also aided by a slight increase in elevation towards Melville's centre.

And thanks to a lack of variation in the day-to-day temperature near the equator, this convergence occurs at the same time every afternoon during wet season.

The now rapidly upward-flowing column of hot, humid tropical air then cools and condenses, giving birth to a cumulus congestus cloud, which eventually rises high enough for ice particles to create the friction required for lightning.

And thus, Hector the Convector, now a mammoth cumulonimbus cloud, is born.

Viewing Hector online

Meteorological advances mean living in the Top End is no longer a requirement for appreciating Hector's daily eruption in the wet season.

Hector can be viewed remotely using observational instruments like radars and satellites, and modern modelling can predict the localised temperature, wind and moisture conditions that will ensure his formation.

For example, the satellite loop above shows small cumulus clouds converging towards the centre of the islands as the sea breeze moves inland, and the resulting inland clash of airstreams which triggers a larger storm cloud.

High resolution modelling also picks up on the daily temperature contrast and wind fields which contribute to Hector's development.

During the next six months, as long as monsoon winds or cyclones are not blowing, Hector the Convector will spawn on most days.

That is before May arrives and the dry season south-easterly winds off the mainland send Hector back into a deep hibernation for the austral winter.