"He was in shock," Mr Christensen said.
It was not the first time trucks had been picked up by high winds at that corner, Mr Christensen said: "I've seen a few. Last time, two trucks rolled on this corner."
Masterton Fire Station senior officer Paul Thompson said the area was windy during storms, as he warned staff to be careful.
"The wind drops off the Tararuas," he said.
In the past, police had been forced to close the road to heavy traffic and campervans when the winds had whipped up to high speeds, Mr Thompson said.
However, Masterton traffic policing sergeant Chris Megaw said the highway wouldn't be closed at this stage: "The problem is, one minute the wind can be high and 10 minutes' later it's all calm."
The driver yesterday had been lucky the truck itself hadn't slammed on to its side, Mr Megaw said.
"[The wind] has lifted the trailer and the driver has lost his steering."
The truck had been equipped with a swivel join rather than a tow bar, which had saved the truck from going over.