the centerAt() method expects a point geometry object.
//pass long,lat and don't forget to load the appropriate AMD module
map.centerAt(new Point(-118.15, 33.80));
//or
map.centerAt(new Point(-118.15, 33.80, new SpatialReference(wkid: 4326)));
this is mentioned in the API reference: https://developers.arcgis.com/javascript/jsapi/map-amd.html#centerat
the object can be constructed using WGS84 coordinates without specifying a spatial reference, but it doesn't hurt anything to include it.
https://developers.arcgis.com/javascript/jsapi/point-amd.html