The rainy winter in the Bay could be soon be replaced by drought conditions caused by El Nino.
Niwa agricultural climatologist Alan Porteous said El Nino was very much on the cards - all the signs were there and major climate agencies believed one would develop between now and September.
The Japan Meteorological Agency this week confirmed the onset of an El Nino. NIWA is also tipping an El Nino to develop in the wake of the La Nina, which created the often moist easterly weather pattern, dissolving and meteorologists are waiting to see if it fully develops.
"The 'super wet' of the past few months has seen a lot of slips and slope stability has been at a worrisome point," Mr Porteous said.
Mr Porteous said: "But what we don't want now is a rapid switch to really dry conditions - that would exacerbate the soil conditions already caused by the saturation, and could then see soil dry out so rapidly that it cracks up and makes it more vulnerable to the next heavy rain."
The news has concerned farmers with Hawke's Bay and national Federated Farmers President Bruce Wills saying a dramatic switch from super-wet to super-dry conditions would be devastating for farmers.
El Ninos usually see an increase in drier, westerly winds in summer for the North Island, and the possibility of drought on the East Coast which could hammer grass that has adapted to exceptionally wet weather in the past two months, Mr Wills said.
"In wet conditions the roots of these plants get a bit lazy and hang around the surface, and if it suddenly goes dry it can suddenly go from feast to famine. History does tell us that weather patterns balance out - the risk of having a dry patch after a wet patch is increased.
"As a farmer I am very conscious of it and I'm thinking as I approach spring I need to keep my grass covers up because so far this year I have had more than double my normal average annual rainfall and I have records going back years - this wet is an extraordinary event.
"So the law of averages says the next six months being as wet as the last have to be much lower."
He said farmers should budget their feed carefully, keep a flexible regime in place and listen to the weather forecast.
"It is hard to be concerned at the moment because the ground is soggy, but Hawke's Bay has dry summers and while we haven't had one for two years you could probably say one will turn up at some stage."
The outlook through to November was for average or slightly above average temperatures and a return to normal rainfall levels, Mr Porteous said.
But as the days lengthened the cold intensified - Mr Wills put off lambing on his Te Pohue farm until mid-September.
"Regularly during the last two weeks of August we get the last vicious kick of winter."
But this may not happen this year if MetService's just-released long-range forecast for Hawke's Bay stays on track, with the last official week of winter shaping up to be the first true taste of a sunny spring.
After a month of on-again off-again rain, a ridge of high pressure is shaping to break its way through what forecaster Daniel Corbett described as "blocking" lows.
The lows had effectively ruled the weather roost, but the latest movements may be bringing that situation to an end.
The weather is set to begin clearing on Saturday, with sunshine and northeasterlies, along with temperatures of 16C, forecast for the Bay.
On Monday the northeasterlies are set to be replaced by northwesterlies, with a rise to 17C and more sunshine, although there is the chance of a shower south of Hastings on Tuesday and Wednesday.
Napier is set for 17C and sunny skies, with little wind, through until the last day of winter - August 31.
But the forecast is not so promising for Southern Hawke's Bay, with the all-too familiar showers spread throughout the week, and temperatures around 13C to 14C.
- additional reporting: Gisborne Herald
