Guess Monday

Every Monday NOAA publishes one number that El Niño watchers wait for: the weekly Niño 3.4 sea surface temperature anomaly. Guess it before Sunday night, to one decimal. When NOAA’s file updates, every guess is scored against it automatically.

Rules

• One guess per browser per week, to 0.1 °C. It cannot be changed once sent.
• Guesses close on Sunday at 23:59 UTC. NOAA usually publishes on Monday; after a US federal holiday it can be a day late, and the round simply waits.
• Points: exact 10 · off by 0.1 → 7 · 0.2 → 5 · 0.3 → 3 · 0.4 or 0.5 → 1 · further → 0. The season board adds them up; ties go to the earlier guess.
• The result is NOAA’s number in its weekly file on the day it first appears. If NOAA revises it later, the round is not rescored.
• No prizes and no money — it is a game of skill for its own sake, not a lottery or a bet.
• No account. We store the nickname, the guess and a random id kept in your browser — nothing else (privacy). Clearing your browser data starts you fresh. Nicknames that are rude or pose as an agency are refused or removed.

Want a head start? The live map shows daily sea surface temperatures, and the status page lists every index with its date.