SSH - Altimetry
The forecast height of the sea surface — warm eddies stand up as hills, cold ones sit in bowls, packed contours mean current. It includes the tide, so it will not match the satellite height layers.
Updates daily; forecast in 3-hour steps
More detail
Captains use this layer to find eddies and their edges. To find an eddy, look for a closed hill or bowl; the current is strongest around its outside, not over its middle.
The forecast comes from HYCOM (U.S. Navy model), and RipIQ puts it on the map. Its error is in exactly where it puts a feature on a given day. Each value covers a square about 5 nautical miles across. The layer covers the Gulf of America, the East Coast and Baja.
The tide is in it, so when you step through one day's frames, much of the change you see is the tide coming and going. To follow an eddy, compare the same time of day from one day to the next.
On the website the crosshair readout gives the height in whole inches when your depth unit is feet, and in meters otherwise. In Layer Settings, fix the Range to keep one color meaning one height from frame to frame.
How fresh it is. The model starts one new run a day, and the newest run normally started between one and four days ago. There are eight frames a day, three hours apart, and the days after the run date are forecast, up to 7 days ahead.
How it relates to the other sea level layers. SSH (DUACS) and SLA (DUACS) are satellite measurements of the sea surface with the tide taken out, about a day old, showing the big features only, about 95 nautical miles across and larger. Use them for a measured, tide-free picture of the big eddies, and this layer for finer detail and for the days ahead. Sea Level Anomaly is this same forecast shown as the difference from its long-term average. Currents is the speed of the water in the same forecast.
The numbers
| How often it updates | Once a day, as 8 frames, three hours apart |
| How fresh it usually is | The newest frame is from a run started between one and four days ago |
| How detailed it is | About 5 nautical miles per grid cell. Surface only |
| Where it covers | Gulf of America, East Coast and Baja. Outside the regions the map shows the chart alone; the layers stop at the region's edge. |
| How far back and forward | 8 days back and up to 7 days ahead |
| Includes the tide? | Yes. The satellite height layers do not |
| Observed or modeled | Modeled. It never goes blank for cloud |
| What you see on screen | The height of the sea surface, tide included |
Source: the HYCOM model.