Conditions
Info
Every slider is yours to play with. Each time the page loads, they start at live San Francisco conditions; reload to go back to them.
Tide and undercurrent: the tide at Golden Gate (NOAA station 9414290), calculated in your browser with NOAA's own harmonic-constant method, using all 33 published constants. Tested against NOAA's official predictions: within 0.07 ft and 2 min. Rising water pushes toward shore, falling water pushes seaward.
Wind, swell height and swell period: the National Weather Service marine forecast for this hour, for the water just outside the Golden Gate. Wind is the part blowing onshore (from the west) or offshore. Air pressure: the latest reading at San Francisco International Airport. Each 1 mb drop raises the sea about 1 cm.
Fetch and the Kelvin / El Niño offset have no live source. The offset starts at +1.0 ft: NOAA's Oct 8, 2026 update reports a strengthening El Niño (Niño-3.4 at +2.1 °C), and San Mateo County says the ocean is running 1–2 ft above the tide tables this winter.
Wave math: wind waves use a standard fetch-limited formula (JONSWAP): height ≈ 0.0016·U·√(F/g), capped at a fully developed sea. Breaking height for swell and wind waves uses Komar–Gaghan: Hb = 0.39·g0.2·(T·H₀²)0.4. Longer periods make longer, faster waves. On-screen, the water level sets how high the sea fills the frame, breaking height sets the swell size, and the period sets wavelength and speed. Foam and spray use the Doom-fire rule. Rightward wind means onshore.
Plunge is the same sea and sliders, stood on end: a tall column, about 100 pixels wide, with the column heights stretched to fill it, so you see each wave from the deep water at the bottom up to its foam tip. Two quick taps for full screen; two more to come back.
This pixelated wave effect is a hat tip to the fire procedural animation in the PlayStation (PSX) port of Doom and in Doom 64 on the Nintendo 64.
Sources: NOAA Tides & Currents 9414290 · NOAA CPC ENSO discussion · San Mateo County king tide notice
Heights above mean lower low water (MLLW); tap the tide height to switch between US and metric units (feet / meters, °F / °C, mph / km/h). A minus tide drops below that line, the best time for tidepools. Tides are astronomical predictions; wind and swell change the real water level. Weather from the National Weather Service. Not for navigation.
Weather and wind icons: Phosphor Icons. Tide arrow: AIGA symbol signs. Moon icons: Weather Icons by Erik Flowers.