"We think that this El Nino - and it's already very strong - has a distinct possibility of being a top three, top four El Nino," said Niwa forecaster Chris Brandolino.
While Niwa won't go as far as predicting drought, they say there is "an elevated risk" of drought.
Rural firefighters and farmers are now being told to prepare for the worst.
Equipment is being readied, staff trained, and awareness campaigns are being launched in danger areas, according to National Rural Fire Officer Kevin O'Connor.
"Around the country, rural fire authorities are already actively planning for this coming fire season which is certainly fronting up to be pretty dry and pretty extreme," he said.
Fire restrictions and bans will likely be imposed earlier than usual.
Forestry companies and rural communities are being encouraged to prepare now.
"If farmers and foresters want to burn, they should think about doing it in the next month, and get some advice from their local rural fire authority," Mr O'Connor said.
Farmers need to be checking their records or asking neighbours for advice in order to prepare for the big dry, Federated Farmers' spokeswoman for adverse events Katie Milne said.
"It's all about having plans and strategies in place and being aware that things could be very bad," she said.
Lifestyle farmers also need to ensure they have enough feed for their pets, Ms Milne said, or else be prepared to move them on.
If the drought begins to take its toll on farmers, they should seek help.
"Droughts can be insidious when it's day in day out, and you can't do anything about watching your income and assets not doing much," Ms Milne said.
"It's important that we stick together."
Primary Industries Minister Nathan Guy said he will be "keeping a close eye" on how the El Nino develops.
He echoed Federated Farmers' position that carefully planning for the possible drought is key.
"Farmers should continue work with their advisers and industry bodies who are best placed to provide expert advice that is appropriate to their needs on how best to prepare."
KEY INFORMATION TO SUPPORT FARMER DECISION MAKING
• Rural Support Trusts - 0800 787 254 for information and support.
• DairyNZ - 0800 4 DAIRY NZ (0800 4 324 7969) for the specific DairyNZ Farmer Information Service. Specific drought management information is available on their website.
• Beef + Lamb - 0800 BEEFLAMB (0800 233 352) for specific guidance for Beef + Lamb farmers. Specific drought management information available on their website.
• Ministry for Primary Industries - What is a medium scale adverse event, and what does it mean? Find out on their website.
• Federated Farmers of NZ - 0800 DROUGHT (0800 376 844) for the Feed list (for matching feed supply/demand). Online specific drought support.
• Rural Women New Zealand - 0800 256 467. For local community events and support visit their website.
• NIWA seasonal outlooks.
• MetService's Monthly Outlook.
Source: Federated Farmers.
