"The heaviest falls, in particular, are in Northland and northern Auckland," MetService meteorologist Rob Kerr said.
"The warm air which has been pulled around and is feeding that cyclone is going to actually move above upper parts of Auckland and Northland on Friday.
"There's been a lot of doubt [the cyclone will] pass this whole time and the [models are] coming into line now, it's staying up north."
The rain, which is expected to be heavy at times, will be a welcome relief for farmers in the extremely dry Northland area.
Niwa warns there might be flooding in parts of the northern North Island due to excessive runoff hitting the dry, concrete-like ground.
NZ Transport Agency is urging motorists to take care on roads in the Northland and Auckland area tomorrow with summer ice a potential hazard.
"After an extended run of very hot and dry summer days we may initially experience very slippery road surfaces," system manager Wayne Oldfield said.
"Even a very small amount of light rain can make the roads very slippery after a long dry spell.
"In fact, it can be more hazardous than heavy rain because grime and exhaust particles that have built up on the road take longer to be washed away."
Parts of Westland and Fiordland have already been doused with rain today due to a slow-moving cold front which should move northeast this morning.
"There is a slow-moving front lingering over the west coast of the South Island and we have a watch in place for that," Kerr said.
"That's affecting the ranges south of that in Westland and Fiordland but that's going to ease (on Friday) morning.
"It's going to move a bit further north but it will bring showers to eastern parts of the South Island as well, so most places will see some participation tomorrow."
Friday's weather outlook
• Whangārei: Rain developing early morning, possibly heavy, easing overnight. Northeast strengthening, changing northwest evening and southwest overnight. High 24C, Low 19C.
• Auckland: A few showers. Rain spreading south from afternoon, possibly heavy from evening. Northeasterlies strengthening. 25C, 19C.
• Hamilton: Cloudy with one or two showers, becoming more frequent from afternoon. Northeast breezes. 26C, 17C.
• Tauranga: Cloudy with a few showers, turning to rain by evening. Northeasterlies strengthening, changing gusty southeast overnight. 25C, 19C.
• Napier: Cloud thickening, an evening shower likely. Northerlies. 29C, 18C.
• New Plymouth: Occasional rain. Northerlies. 23C, 15C.
• Wellington: Mostly cloudy, a few showers in the north. Rain developing in the afternoon. Northerlies, strong for a time. 22C, 15C.
• Christchurch: Fine at first then cloud increasing from afternoon. Northwesterlies change southerly in the afternoon. 28C, 11C.
• Queenstown: Cloudy with a chance early shower then fine. Westerlies. 20C, 7C.
• Dunedin: Early rain, then a few showers from afternoon. Northwesterlies change southeast in the afternoon, then die out evening. 20C, 10C.
• Invercargill: Early rain, then fine spells and evening showers. Westerlies, strong at times. 16C, 8C.
