WeatherWatch.co.nz has issued a Storm Alert for Auckland city, the first one for 2011 and the first one since the big September storm last year.

Storm Alerts are issued by the weather news authority only once or twice a year during severe weather events as an indication that the incoming severe weather could pose a risk to people and property.

WeatherWatch.co.nz says one positive for Auckland is the fact that heavy rains generally tend to drain away well from the hilly city, but other surrounding regions such as Northland, Bay of Plenty and Coromandel Peninsula are at a higher flood risk due to the terrain.

New Zealand’s MetService has this afternoon stepped up their official rain warnings for Auckland city and surrounding regions as rain arrives earlier than predicted.

The state owned forecaster says Auckland can now expect between 150 and 250mm across much of the region.   Earlier today they predicted 100 to 200mm.

Rainfall predictions for Coromandel Peninsula and Bay of Plenty are up to between 350 and 400mm.

WeatherWatch.co.nz says that the rain, associated with a deepening sub-tropical low, will set in and become heavier this evening and overnight.

The low is likely to deepen to a point where gale force winds are generated.  WeatherWatch.co.nz says eastern Northland, eastern parts of Auckland, the Hauraki Gulf and eastern Waikato will be most exposed to the strong winds, expected to arrive later on Sunday as the low deepens overnight.

Head weather analyst at WeatherWatch.co.nz, Philip Duncan, says people in low lying areas should be aware the predicted rainfall totals are high enough to cause serious flooding.  “These totals, of up to 350 and 400mm across the Coromandel and Bay of Plenty ranges are very high and could lead to serious flooding in low lying areas downstream”.

“In other areas, such as Auckland, heavy rain could make driving hazardous”.

Mr Duncan says this sub-tropical low brings a much greater threat to the upper North Island than ex-cyclones Zelia and Vania did last week.

MetService says the rain is expected to become persistent and heavier from Northland to Gisborne this evening as a trough of low pressure just northeast of the North Island deepens.

“This widespread heavy rain is associated with a subtropical low which is expected to approach the country during Sunday, and lie over the upper North Island by midnight. A Heavy Rain Warning is now in force for most regions of the North Island from Northland down to Waitomo and the central North Island high country, and across the Bay of Plenty to Gisborne and Hawkes Bay. Taranaki, the eastern hills and ranges of Wairarapa and the Tararua Ranges, are currently not included in the rain warning, but accumulations in these areas could approach warning amounts during Sunday so a heavy rain watch will be maintained for them”.

MetService forecaster Gerard Barrow says as the low approaches and moves onto the upper North Island during Sunday, north to northeast winds are expected to become strong or reach gale force in Northland, Auckland, Coromandel Peninsula and the Bay of Plenty.   “It is possible these winds could gust to damaging severe gale for a time in exposed places, so a wind watch for these areas will be maintained”.

“Considering the significant impact this weather event could have on parts of the North Island, people are advised to keep up to date with the latest forecasts and warnings”.

Click here for the latest warnings and watches