General Malik bin Suleiman al-Muamri, head of the country's civil defence, said the most powerful portion of the storm was expected on Thursday.
Al-Muamri said the storm, which is heading northwest through the Indian Ocean towards the east coast of Oman, was expected to send waves reaching 10m against the shores of Masira island.
About 500 people were killed on Masira when a cyclone hit in 1977.
According to Tim Roche, a meteorologist, Gonu currently has winds of 260km per hour, with gusts up to 315km per hour.
Roche said that Gonu is forecast to hit Oman with sustained winds of around 185km per hour, before moving north over the Gulf of Oman into southern Iran.
With those wind speeds, the storm would be the strongest cyclone to hit the Arabian Peninsula in recorded history since 1945, he said.
Excuse or reason
Oil prices edged upwards on Monday, but Tom Kloza, chief oil analyst at the Oil Price Information Service, said he doubted the increase could really be attributed to Gonu.
"I don't know if you can really attribute any of the gain to the cyclone," he said.
"It's an excuse, as opposed to a reason, for the rise in prices."