The mythical creature, subject of much awe and attention during its unveiling and initial jaunt over Lake Burley Griffin on Saturday, was due to surprise residents of Canberra as they woke on Monday morning to see it float by their window.

But the titillating voyage planned for a dawn cast-off could be forced from the sky by a forecast of rain and wind.

Canberra Centenary organisers said enthusiastic whale-watchers should keep an eye on their Twitter, Facebook and webpages for the final word early in the morning.

If the Monday outing is harpooned by the wet, the creature will remain in Canberra and await a clear day, possibly until next weekend.