He worked his way through to a third-place finish, and in the final race of the day led all the way.
"I couldn't be happier," he said.
"To be half way through both the North Island and New Zealand series and to be leading both is exactly what I would have wanted at the start of the season."
He said the results were the best way to "pay back" his sponsors, Bay Mazda and NAC insurance.
"I just hope I can continue to hold on to this form and a bit of luck."
In the opening round of the six-round series last Labour Weekend, Forster picked up three wins from as many starts and is now focused on keeping the form hot.
The next round of the North Island series will be staged this month at Manfeild Motorsport Park, then on to Hampton Downs and finally Taupo.
The New Zealand Series finishes at Ruapuna in Christchurch in April.