Corridor Pressure
Elevated
Binding leg: Madeira.
The corridor is only as navigable as its most-pressured link.
Mainstem · Óbidos
Normal
Forecast 59.1th pctile (Normal) · observed 83th
Amazon trunk (Óbidos) — the shared artery both barge legs feed into.
Tapajós · Itaituba
Ample
Forecast 66.7th pctile (Ample) · observed 82th
BR-163 → Miritituba/Itaituba → Santarém — the fast-growing Arco Norte leg.
Madeira · Humaitá
Elevated
Forecast 30.2th pctile (Elevated) · observed 95th
Porto Velho → Itacoatiara — Rondônia / west-Mato-Grosso soy & corn.
Alongside ENSO: The model's ENSO input is the Feb–Apr RONI (-0.45, cool — the season that best forecasts the Amazon low). But the Pacific has warmed since: the latest reading (AMJ 2026) is +0.47 and still rising — a developing pattern, the same cool-late-winter start that preceded the record 2023 drought. If it holds into the dry season, compound low-water risk on the mainstem and Tapajós rises above the current Atlantic-led forecast. On the mainstem and Tapajós, a warm Tropical North Atlantic and El Niño compound — the severe lows need both. The Madeira leg responds to whole-basin Atlantic warmth and is largely ENSO-agnostic.
Red zone (≤10th) = Severe, amber (≤33rd) = Elevated pressure. Forecast is the modelled Sep–Nov low from the spring ocean state; Observed is the most recent river reading. A barge corridor is only as open as its weakest link.
Itacoatiara stage · Aug 2026
12.6 m · 41th pctile
Normal (−2.4 m vs the 1991–2020 average for the month)
Just below the mouth of the Madeira, the Amazon squeezes past the Passagem do
Tabocal — not a shifting sandbar but a fixed rock ledge that cannot be
dredged away. It sits immediately upstream of the Itacoatiara terminals, the point where
grain barges off the Madeira (Porto Velho) and the Tapajós (Miritituba) hand their cargo
to ocean-going vessels. When the dry-season low exposes the ledge, the whole corridor's
export throughput funnels through a single shallow gate: in the 2023 record drought a
tanker sat grounded here for 23 days and DNIT emergency-dredged an 8 km reach; in 2024
the government committed R$138 million to dredge a 12 km stretch at the Tabocal.
We read it off the Itacoatiara gauge — the mainstem stage right at the transfer point.
Its September–November low answers to the same North Atlantic and El Niño forcing that
drives Óbidos (out-of-sample skill +0.79), so this is a corroborating observed
gate on the mainstem; the mainstem forecast is anchored on Óbidos discharge above.
A warm Tropical North Atlantic pulls the Atlantic ITCZ north, starving the Amazon of
wet-season rain and deepening the dry-season river low. Measured in spring, it forecasts
the September–November low months ahead. On the mainstem and Tapajós, El Niño
compounds the Atlantic signal; the Madeira responds to whole-basin Atlantic warmth.
Boreal-spring (Apr–Jun) warmth in this box precedes the Sep–Nov Amazon low by ~3–5 months. The red band (≥ +0.4°C) is the dry-risk regime that drove the 2005, 2010 and record 2023 droughts. Self-computed from NOAA OISST v2.1, 1991–2020 baseline (see fetch_atlantic_index.py).
Óbidos mainstem discharge, leave-one-out (each year predicted from a model fit on all others). Every major drought (2005/2010/2023/2024, red diamonds) was flagged in the driest quartile months ahead. Points near the dotted line = accurate. Out-of-sample skill r ≈ +0.76.