Article summary: NIWA’s September–November 2025 outlook leans La Niña-like, but still leaves room for a near-neutral season. Here’s how to translate those probabilities into simple Plan A/B/C feed plans, clear trigger points, and a weekly “what to watch” routine so you can protect utilisation, quality, and pasture persistence.
Seasonal outlooks are not a promise, they’re a head start
A spring outlook won’t tell you what happens next Tuesday. What it can do is load the dice, and help you decide what you will do if the season runs wetter, drier, or faster-growing than normal.
NIWA’s September–November 2025 outlook is a good example. It signals a tilt toward La Niña-like patterns, even though “neutral” remains in play depending on which index you use.
Your job is not to predict spring. Your job is to be ready for it.
The Spring 2025 signal in one line
NIWA’s message for Sep–Nov 2025 is essentially:
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La Niña is favoured in the background, but not locked in, and
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New Zealand is likely to be warm-leaning, with region-by-region rainfall differences and a real watch-out on soil moisture in parts of the North Island.
A few specifics worth noting (because they influence on-farm risk):
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NIWA notes international guidance favouring La Niña through spring and early summer 2025–26, and an experimental RONI outlook putting La Niña at about a 60% chance over Sep–Nov 2025.
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At the same time, NIWA’s outlook also states ENSO-neutral is still the single most likely outcome on the traditional Niño 3.4 framing (57% chance).
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NIWA forecasts soil moisture and river flows below normal or near normal for the north and east of the North Island (and the west of the South Island), even where rainfall odds are not strongly “dry”.
Translation: don’t anchor your plan on “it’ll be wet” or “it’ll be dry”. Anchor it on what you will do when your pasture and soil data confirm which way it’s actually going.
How to read probabilities without overthinking them
NIWA expresses seasonal forecasts as probabilities across three buckets (above, near, below average). If there were no signal, each bucket would be ~33%.
So when you see a 45% chance of “above average” temperature, it means:
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“Above average” is favoured, not guaranteed
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You can still get cold snaps, wet weeks, or dry spells inside that 3-month average (NIWA explicitly calls this out).
A useful mental model is:
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Probabilities inform preparation
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Your weekly measurements inform action
Step 1: Convert the outlook into pasture risks you can manage
Instead of thinking “La Niña”, think in three pasture-risk buckets:
1) Dryness risk (slower growth, longer recovery)
Watch-outs:
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Rotation length starts stretching without you choosing it
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Residuals slip, or cows start chasing the last bite
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You stop hitting your cover targets even with “normal” management
Why it matters in this outlook:
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NIWA flags soil moisture being below nor mal or near normal in parts of the North Island, even with mixed rainfall probabilities.
2) Wetness risk (utilisation losses, pugging, quality dilution)
Watch-outs:
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You have grass, but you can’t harvest it well
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Post-grazing residuals climb because cows cannot clean up
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Pasture damage shows up as you head into summer (and you pay for it later)
3) Fast-growth risk (quality loss if you miss the moment)
Watch-outs:
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Covers blow out quickly
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Heading arrives before you’ve adjusted rotation and conservation
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You end up “managing surplus” instead of “banking quality”
Step 2: Build Plan A / Plan B / Plan C feed plans (and pre-decide your triggers)
You’re aiming for three simple plans you can switch between without drama.
Plan A: The “most likely” spring plan
This is your default if your data looks broadly seasonal.
Focus:
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Keep rotation discipline (avoid drifting into reactive grazing)
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Convert surplus early (quality first, quantity second)
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Keep the system simple so you can change fast if conditions shift
Trigger points to stay in Plan A:
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Soil moisture is stable or improving week to week
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Pasture growth rate is tracking close to demand (your usual spring balance)
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Residuals and pre-grazing targets are being hit with normal effort
Plan B: The “drier-than-expected” plan
This is about protecting pasture and avoiding a spring blowout that becomes a summer feed hole.
Do this early (before it hurts):
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Tighten grazing decisions around residuals (protect leaf, protect regrowth)
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Bring supplements forward sooner rather than later (to stop a slow bleed)
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Reduce “optional” demand (defer non-essential stock moves if you can)
Trigger points to switch to Plan B:
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Soil moisture trend is down for two consecutive weeks
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Growth rate has been below demand for two consecutive updates
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You’re missing residual targets despite “trying harder”
Plan C: The “wetter / stormier-than-expected” plan
This is about protecting utilisation and persistence when the paddock is telling you “not today”.
Do this early:
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Put a pugging plan in place (stand-off area, on-off grazing, sacrifice strategy)
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Prioritise paddocks that can take damage less, and protect those you cannot replace
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Keep quality in front of you (don’t let covers get away because you can’t travel)
Trigger points to switch to Plan C:
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Heavy rainfall events stack up and soil is not draining between them
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Residuals climb because cows can’t clean up
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You’re leaving ruts or seeing treading damage that will affect summer
Step 3: What to watch weekly (your 10-minute Monday dashboard)
The goal is a short list you actually check.
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Rainfall (actual + next 7 days)
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Weekly totals matter less than “patterns” (clusters vs gaps)
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Soil moisture trend
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Don’t just look at today, look at direction
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NIWA’s outlook specifically highlights soil moisture as a key risk lens for spring 2025.
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Pasture growth rate
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Growth rate is your early-warning system
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If growth and demand diverge, you act, you don’t wait
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Feed wedge shape and trajectory
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Is the whole wedge lifting? (surplus)
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Is the top falling away? (quality and allocation issues)
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Is the base thinning out? (future risk)
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Rotation length and residuals
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Residuals tell you whether you’re truly in control, regardless of what the forecast says
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Supplement position
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Inventory, quality, and how quickly you can deploy it if Plan B triggers
Tip: If you want a “between seasonal outlooks” guide, NIWA also points farmers to sub-seasonal tools (like NIWA35) to keep an eye on shorter swings.
Mini-example 1: North Island NZ-style system (decision logic)
Think a pasture-based dairy platform where spring growth can move fast.
NIWA’s Sep–Nov outlook for the upper North Island leans:
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temperatures near average or above average
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rainfall near normal or above normal
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soil moisture near normal or below normal
So your decision logic could look like:
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Start in Plan A, but treat soil moisture as the “truth metric”.
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If growth lifts and covers rise, pull the surplus trigger early (conservation or graze tighter to hold quality).
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If rainfall happens but soil moisture still trends down (common on lighter soils or after a deficit), switch to Plan B earlier than you normally would, because waiting costs you persistence and quality later.
In practice, you’re not reacting to the word “La Niña”. You’re reacting to:
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growth rate versus demand, and
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soil moisture trend versus your normal spring pattern.
Mini-example 2: Southern Australian grass-based system (decision logic)
Pick a cool-temperate system (dairy, beef, or sheep) where spring rainfall and trafficability make or break utilisation.
A La Niña tilt often increases the chance of wetter conditions in parts of southern Australia, but it is not a guarantee and it varies by region. The Bureau of Meteorology’s La Niña composites show some southern areas (for example NE Tasmania, northern Victoria, eastern South Australia) tending wetter in La Niña years.
Your decision logic:
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Plan A is about capturing growth and holding quality.
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Your real risk is that a wet run pushes you into Plan C conditions where you have feed but can’t utilise it without damage.
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So you pre-decide your wet triggers:
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if soils stay wet between events, you activate stand-off or on-off grazing
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if residuals climb, you shift allocation and prioritise paddocks that can handle it
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if covers are rising but harvest is messy, you move earlier on conservation windows
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Also keep the humility clause in mind: Australian rainfall is influenced by multiple climate drivers, not ENSO alone, so local monitoring still wins.
What forecasts can’t tell you (and how to avoid getting caught out)
Seasonal outlooks are averaged over three months. They can’t reliably tell you:
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Which week the rain lands
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How intense rainfall events will be on your farm
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Whether you’ll get a “two-week hole” in an otherwise normal season
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How your specific soils, aspect, and pasture base will respond
NIWA is explicit that wet and dry periods will still occur inside the season, even when the 3-month average leans one way.
So the right posture is:
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Use the outlook to prepare your plans
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Use weekly farm data to decide when to switch plans
A simple routine that turns climate odds into action
If you want this to be genuinely useful, keep it lightweight:
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Once per week (10 minutes):
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check rainfall (last week + next week)
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check soil moisture trend
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check growth rate versus demand
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check whether you’re tracking your residual and rotation targets
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choose Plan A, B, or C for the next 7 days
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That’s pasture risk management: not prediction, but prepared decision-making.
If you want to operationalise this in Pasture.io, set up your weekly view around:
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growth rate trend
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feed wedge trajectory
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rotation length and target residuals
rainfall and soil moisture direction
So the “switch” from Plan A to B or C is driven by facts, not gut feel.
- The Dedicated Team of Pasture.io, 2025-10-23