SEVERE Tropical Cyclone (TC) Marcia is one super storm that caught Bureau of Meteorology forecasters by surprise.
Up until about mid-afternoon on Thursday, meteorologists were watching the storm tracking at category 1 strength, with sustained winds of just over 100 kilometres an hour.
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Then, about 4pm, forecasters watched as the cyclone started to slow and its projected intensity soared.
According to data compiled by the Space Science and Engineering Centre at the University of Wisconsin-Madison in the US, the projected wind speed for Marcia jumped to as much as 230km/h, well into the category 5 range.
The Bureau estimates the storm crossed the coast at category 5 strength on Friday morning.
Cyclone Marcia was downgraded to category 4 by the Bureau of Meteorology at its 11am briefing on Friday.
Kevin Walsh, a tropical cyclone expert at the University of Melbourne, said it was a slowdown in Marcia's march towards the coastline that triggered the rise in intensity.
During slowdowns, cyclones can either pick up more heat or they can self destruct.
"The crucial factor is how much heat is available there for the cyclone to intensify," Associate Professor Walsh said. "It certainly intensified unusually rapidly."
In Marcia's case, favourable upper air conditions allowed the storm to speed up its rotation, drawing up more air "like smoke rising in a smokestack", one meteorologist said.
Rob Webb, regional director of the bureau in Queensland, said the rate of Marcia's strengthening was "remarkable" but added "it's too early to pinpoint exactly why".
The focus of the bureau remains on dealing with the current challenges posed by Marcia, including extensive rain and damaging winds over a wide region, Mr Webb said.
Sea-surface temperatures off eastern Australia have been unusually warm, particularly off the NSW coast, with temperatures as much 2-3 degrees above average, according to the US National Oceanic and Atmospheric Administration.
Such rapid jumps in intensity have been observed elsewhere, such as in the north-west Pacific, Professor Walsh said.