The £17 million offshore weather monitoring project will start in September with the stations measuring wind speed and direction and temperature and air pressure.
The monitors are in the north and south of the East Anglia zone and consist of a monopile foundation and a steel lattice tower.
The tips of each mast reach 100m above sea level to monitor weather conditions at the approximate height of an offshore wind turbine.
The project was overseen by Aberdeen-based Wood Group with Steel Engineering of Renfrewshire carrying out the manufacturing subcontract.
Programme director Andy Paine said: "We have been developing our plans for more than two years and it is a great achievement to now see the first physical structures being installed offshore.
"The data we receive from the weather masts will provide detailed information that will help us to design the layout of our future projects."
The 1.2GW project will require up to 325 wind turbines and cover an area of 300 square kilometres in the southern North Sea, 43.4km off the Suffolk coast.
Initial survey work is also continuing for the second and third proposed projects, with a further combined capacity of 2.4MW.