Altimetry
Contour lines through the hills and valleys of the forecast sea surface. Tight lines mean a steep slope and stronger current; the thick line is the zero level where high meets low.
Updates daily; forecast in 3-hour steps
More detail
A warm-core eddy stands up as a dome and a cold-core eddy sits in a bowl. Where the lines spread apart the water is slack.
How to turn it on. Altimetry is a button on the bar along the bottom of the map, on the iPhone app and the website. Tap it and black lines are drawn over whatever layer you have up. Tap it again to remove them. The button is off again each time you open the app.
Reading the numbers. The figures along the lines are whole inches if your depth unit is feet and centimeters if it is meters.
Which lines you are looking at. The button follows the tab chosen in Data Layers. With a Forecast layer up, the lines are traced from Sea Level Anomaly, from HYCOM (U.S. Navy model). They change every three hours, from 8 days back to 7 days ahead. With an Observed layer up, the same button draws lines measured by satellite instead, one picture a day and about a day behind. The Observed SLA Contours article covers those. If the measured lines cannot be loaded, the app shows no lines.
How to use it. Closed rings of lines are eddies. Where the lines bunch together is where to look for an edge.
Limits. Each forecast cell is about 5 nautical miles across, so the lines show the Loop Current and the eddies and not small features. Near the coast the lines often stop short of land. The lines cover the Gulf of America, the East Coast and Baja.
Who makes it. RipIQ traces the lines itself, from the HYCOM (U.S. Navy model) forecast.
The numbers
| How often it updates | Once a day, as 8 frames three hours apart, on the "Forecast" tab; once a day on the "Observed" tab |
| How fresh it usually is | "Forecast": the newest frame is from a run started between one and four days ago. "Observed": about a day behind |
| How detailed it is | About 5 nautical miles per cell |
| Where it covers | Gulf of America, East Coast and Baja |
| How far back you can look | 8 days back |
| How far forward you can look | Up to 7 days ahead, on the "Forecast" tab |
| Observed or modeled | Modeled on the "Forecast" tab; satellite-observed on the "Observed" tab |
| What you see on screen | Black lines a fixed step of height apart, 5 cm (about 2 inches). Labeled in whole inches or centimeters. The zero line is drawn thicker |
Source: computed by RipIQ from SSH - Altimetry (HYCOM model).