I Built a Live El Niño Tracker From NOAA's Raw Data — the Part Nobody Tells You

I Built a Live El Niño Tracker From NOAA's Raw Data — the Part Nobody Tells You

A couple weeks back NOAA declared 2026 an El Niño year and said there's a 63% chance it turns into a Super El Niño this winter. I wanted to see the current number for myself — the ONI, the index everyone cites — and quickly found out there isn't a clean live dashboard for it. The data is sitting in a bare ASCII file on NOAA's server.

So I built one. It's at https://elninoguide.com/ — the tracker page there is what this post is about.

The number everyone quotes is the Oceanic Niño Index, or ONI. Here's the part that trips people up: it's not a point-in-time reading. It's a three-month running mean of sea surface temperature anomalies in the Niño 3.4 region of the equatorial Pacific. That means the "latest" value always lags — the August reading isn't real until mid-September, because the June-July-August window has to close first.

NOAA publishes it in a plain text file at cpc.ncep.noaa.gov/data/indices/oni.ascii.txt. The format is one line per year, then twelve columns for the overlapping three-month seasons (JFM, FMA, MAM, and so on). You grab the most recent populated column and that's your headline number. Right now it's +1.39°C for MJJ (May-June-July), comfortably above the +0.5°C threshold that defines an El Niño.

The build itself is deliberately boring: static HTML, a couple of Chart.js canvases for the five-year ONI trend and the Super El Niño comparison, and no backend. I pull the numbers by hand each month when NOAA updates the file. That's it. No cron job, no scraper — just me checking the ascii file and updating one value.

The charts I actually care about:

• the five-year ONI line, so you can see how fast 2026 has climbed (it went from −0.21°C in JFM to +1.39°C in MJJ — one of the sharpest La Niña-to-El Niño flips on record)
• a table of the four Niño regions (1+2, 3, 3.4, 4), because "El Niño" isn't one number, it's a gradient across the Pacific
• a Super El Niño comparison, because the 63% forecast only makes sense against 1997-98 and 2015-16

If you're into weather data or just want to see what a hand-rolled tracker looks like, it's all at https://elninoguide.com/. The full guide part of the site covers what a Super El Niño actually means for different regions, which is where most of the interesting reading is.