Forty years ago today, weather forecasters in WA could only watch as things began to go terribly wrong.

The Bureau of Meteorology (BOM) had been tracking Tropical Cyclone Alby as it moved slowly and steadily south over open water, away from the state's north.

It was expected to follow a well-trodden path; moving over cooler waters, and quickly losing momentum.

But Alby seemed to defy logic, accelerating from 10 to 25 kilometres per hour as it curved towards the coast, passing close to the south-west corner of the state at up to 60kph.

Five people died as wind gusts up to 150kph left a trail of destruction hundreds of kilometres inland from Geraldton to Albany, with widespread flooding and power blackouts.

Two men drowned at Albany when their dingy overturned, another man died when a tree fell on his bulldozer, a woman was killed by a falling pine tree and one man died after he was blown from the roof of a shed.

Fires fanned by the very strong winds burned through an estimated 114,000 hectares of forest and farming land.

To this day Alby is still regarded as the most devastating system to hit south-western WA.

Alby's dangerous extra-tropical transition

Forecaster Chris Blackford was working in Perth when Alby struck.

Chris Blackford says the bureau was not equipped to predict Alby's movements. ( ABC News: Rebecca Dollery )

He said the BOM still had a lot to learn when it came to understanding cyclones in southern waters in 1978.

"The received wisdom at the time was that once cyclones starting heading south into cooler waters they would weaken," Mr Blackford said.

"Alby, as it headed south, changed its structure and that was interpreted as being a weakening sign."

He said Alby was undergoing an extra-tropical transition, becoming a different type of weather system to a cyclone, but one that was just as dangerous.

"As it moved south, a strong cold front dragged Alby to the south-east and it accelerated and actually redeveloped by the time it reached the south-west coast".

Technological advances not enough

Mr Blackford said despite advances in technology, the BOM was unequipped to predict the system's movements.

"We'd just started to get satellite images every three hours, compared to once every 12 hours, which was cutting-edge technology for the time," he said.

"It was a great step forward, but it was very new, and forecasters were still getting used to it."

"It was wonderful technology, but it wasn't enough."

The path of Cyclone Alby, which hammered WA's south-west coast in 1978. ( Supplied: Bureau of Meteorology )

The bureau's Joe Courtney said technology had changed significantly since Alby struck and forecasters could these days provide ample warning of a similar event.

"What has happened since Alby is we have computer modelling, which we can run multiple times to guide us for the forecast," he said.

"Back then we didn't have anything like that available to us, so whilst we could see it, it didn't mean we could work out how quickly it was going to move.

"Nowadays we get images every 10 minutes and we have a host of other satellite technology, such as microwave imagery and water vapour imagery as well to help us."

"We can give up to seven days warning nowadays."

Region yet to see another Alby

Mr Courtney also said the way the BOM communicated with the public had changed dramatically since 1978.

"If an Alby were to happen today, we'd have a much better idea of how to give the public advance notice," he said.

Mr Courtney also said social media and greater interaction with emergency services meant it was very unlikely the community would be left in the dark with regards to an Alby-style event.

But he added that the rarity of an event like Alby meant communicating the severity of a system crossing the state's south-west would still be a challenge.