Science
How to read a water temperature forecast
What the numbers mean, why they change, and how to plan your swim.
5 min read
A water temperature forecast blends satellite observations, buoy readings, and ocean models. The number you see is usually a daily average for the surface layer, not the exact temperature at ankle depth.
What affects the forecast
- Upwelling: wind can push warm surface water away and bring cold water up, especially on Pacific coasts.
- Tides and currents: moving water mixes layers and can shift temperature quickly.
- Time of day: the warmest reading is usually late afternoon; the coolest is early morning.
- Depth: shallow bays heat faster than deep water or open coast.