The low pressure system could now develop into the "perfect storm" if it folds into the remnants of another cyclone, Neville, to deluge farms, orchards and cattle properties and bring relief to coral reefs that were at risk of bleaching.
Olga crossed the coast near Cape Tribulation, north of Cairns, at about 2pm, bringing down trees and flooding roads in the thickly rainforested area.
No injuries were reported, but full-scale disaster preparations were activated as the cyclone approached, menacing communities from Cooktown to the tourist centre of Port Douglas.
The cyclone had almost blown itself out by the time it made landfall as a category-one storm, far weaker than the category-two system, with winds up to 140km/h, that had been expected.
"We haven't had strong winds over land, however there have still been some fairly strong winds further out to sea," said forecaster Tony Auden from Brisbane's Tropical Cyclone Warning Centre.