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The former All Black's contract with the union expires at the end of the season and he has decided against reapplying.
He has been in the job for two years but involved with professional rugby since 1998. It is time to spend some more time with his family.
"I won't be putting my name in the hat," he said.
"It is nothing to do with anything down here. It is more to do with the fact I have been away from my family for two Mitre 10 Cup seasons and they deserve some attention.
"I just want to spend some time with them. My three boys are all growing up ... and also I have a business in Christchurch, so that's my plan.
"I still want to coach and I still want to be involved in coaching. But for the next year it will be at a lower volume rather than a full-on commitment ..."
Canterbury coach Joe Maddock is moving on at the end of the season, but Hewett said his wife, Michelle, would not look at him "very favourably" if he went into another "fulltime gig up there".
"I've been involved with the professional game since 1998 and during that time I've been out for six to eight months because of the rugby campaigns I've been involved in.
"You miss out on family parties, birthdays, weddings and my wife has had to get along to those events by herself which is hard for her. And she has also had to look after the three boys by herself."
Hewett said despite the lean run of results with Southland - just one win in two years - he has enjoyed his stint in the south.
There are still two games to go, and he has made one forced change to his starting side for the game against Auckland at Eden Park tomorrow.
Tauasosi Tuimavave replaces Lewis Ormond on the right wing. Ormond copped a knee to the back from his brother Jackson Ormond during the 19-0 loss to Taranaki.
Southland's focus has been on remaining accurate on defence and offering more on attack.
"It is about going up there and making sure we put on the performance we know we can. I was really proud of the way the guys played for 50 minutes against Taranaki.
"I do think we were on the wrong side of some of the decisions from the referee ... I certainly thought that last try scored was off a forward pass.
"We went up there to win but I thought it was a good performance. It was just that last 20 minutes that let us down for various reasons."
Eden Park, 5.05pm tomorrow
Southland: Josh Moorby, Tauasosi Tuimavave, Isaac Te Tamaki, Ray Nu’u, Rory van Vugt, Marty McKenzie, Logan Crowley, Charles Alaimalo, Matt James, Brayden Mitchell (captain), Mike McKee, Craig Smith, Morgan Mitchell, Greg Pleasants-Tate, Joe Walsh. Reserves: Ryan Carter, Howard Sililtoto, Chris Apoua, Ray Tatafu, Bill Fukofuka, Jay Renton, Mitch Taylor, Seb Wileman.