No other cars were involved in the crash.
Waitemata Road Policing manager Superintendent John Kelly said motorists had to adjust their driving to meet weather conditions.
"There was a beautiful day on Saturday and a very different day today. All that illustrates is Auckland weather in a way - you have to be prepared for anything and drive to the conditions, you can't drive as though the conditions will be the same all the way through."
There was a spate of crashes around the city yesterday and many of them have been blamed on drivers getting caught out on slippery roads.
Mr Kelly said as well as motorists checking their vehicles before longer journeys, they should also watch their following distances, particularly in the wet.
"Once you have water on the road you need to drive more delicately ... And that takes a bit of thinking about."
Meanwhile, an online tribute page for Mr Fitzhenry has been flooded with comments from his friends.
Mr Fitzhenry was struck and killed on State Highway 17 near the intersection with Horseshoe Bush Rd about 9.20pm.
It is understood he was wandering on the road, and police have said he may have been drinking.
Navarda wrote on the RIP Stephen Fitzhenry Facebook page: "I can't help but notice it's rained at least once every day since you left us. It would seem even the sky mourns for you with us. Rest In Peace, handsome prince. We'll see you again."
Another friend wrote: "Rest In Peace. Hope it was peaceful dude. And you're still watching over the people that love you ... and haven't left their side spiritually."
A service for Mr Fitzhenry will be held in Orewa tomorrow.