There are forecasts available. Ocean charts
show an average position.
If your chartplotter
shows you are moving at a different speed than your knotmeter
, and your gps
heading is at odds with your compass
, you might be in an ocean stream.
Simple answer, it's on some charts
In reality, you may want to use it, or cross it as quickly as possible to avoid fighting it.
Get a good navigator. NEVER volunteer to be navigator, it's a thankless job. And you only get respect AFTER the rest of the crew wonders why you said something so early.
Or you went straight to a dark mark, off a strange port..