Rare weather pattern responsible for flood

By JAMES GARDINER

The weather pattern that caused the weekend flooding in the Bay of Plenty was a one-in-10-year event, forecasters say.

The MetService had warned that the severe weather event could be more widespread with the potential to hit Auckland as well as the lower North Island areas still reeling from February's floods.

Forecaster Andy Downs said a very slow-moving north-south front developed on Friday and stalled over Bay of Plenty after linking with a low which developed in the subtropics.

That caused a large amount of rain in a fairly concentrated area, Mr Downs said yesterday.

In 48 hours from Friday morning, Whakatane received 250mm of rain and Rotorua 150mm.

"That's a lot of rain, way over their monthly average even for this time of year," Mr Downs said.

What was unusual was that the rain was just as intense in the low-lying coastal areas as in the hills, which normally would expect rainfall levels 10 times higher.

"So you've got a fully laden river coming down and combining with heavy rain at the lower levels."

The concentration of the weather pattern was illustrated by the much lower rainfall levels over the same period in Tauranga (90mm) to the west and Hicks Bay (29mm) to the east.

The rain shadow effect meant the lower North Island was also doused, Wellington receiving 70mm over 48 hours, Wairarapa 68mm and Manawatu 32mm.

Further north the East Cape and Hawkes Bay continued to cop heavy rain for most of yesterday, with Gisborne receiving 50mm in 10 hours and Mahia 60mm.

"We were relatively lucky," Mr Downs said.

"We put warnings out expecting the rain to track much further west into Coromandel and Auckland, but it didn't.

"That's been the saving grace for the Manawatu, Wellington and the Wairarapa. There was the potential for it to be a lot worse."

He said the Bay of Plenty forecast was for at least two dry days to start the week.