Tries to Brendon O'Connor and Ryan Tongia gave Hawke's Bay a handy lead, which they should have been able to close out.
After suffering two losses from their first three contests, this victory would have been a good confidence boost for a Northland side who like to throw the ball around and play with ambition, even if the conditions don't warrant it.
The Taniwha will look to build on this result when they meet Otago in Dunedin next Wednesday.
Meanwhile, Hawke's Bay will need to lift their performance when they defend the Ranfurly Shield against Otago on Sunday, September 14.
Nerves of steel: Northland first-five Dan Hawkins had it all on his shoulders but came up big when his team needed him most. Cracking kick to win it.
The big wet: The heavens opened in Whangarei and they didn't let up. The ball resembled a piece of soap throughout the contest, which made life tough for both teams.
Northland 23 (Dan Pryor, Michael Stolberg tries; Dan Hawkins 3 pen, 2 con) Hawke's Bay 21 (Brendon O'Connor, Ryan Tongia tries; Ihaia West 2 pen, con, Matt Berquist pen) halftime: 11-6