I just checked the weather report for an area of the Jalisco coast. It predicts winds today from the west. Tommorrow it predicts wind from the SSE. How do meterologists know which direction the wind will blow in the next day or so?
Which way the winds blow is a function of the weather in that location at that time. The main component is surface pressure relative to surface pressure in other locations; around a surface low the winds will go one way, around a surface high, they go the other. Frontal boundaries often result in predictable changes in surface winds.
In short, they know this because it’s a function of what they can predict with reasonable accuracy, unlike precipitation, which often is unpredictable. 
OK thanks. Here’s the scenario. Right now the weather is crystal clear here. The nights are cool (17º C/62º F) and the days are warm (27º C/82º F). The ocean is warm (24º C). I always thought high pressure over land near the ocean is what kept clouds/storms offshore. Yesterday we had pretty strong winds from the west. Today the wind has already started blowing from the west but so far seems lighter. The Weather Channel predicts winds coming from the sse tomorrow. Since we have a very large gathering for Christmas on the beach late tomorrow afternoon, we are hoping that the prediction is correct. A strong west wind will really put a damper on things.
Look at a surface frontal map with isobars to get an idea of what is likely to cause a shift in surface winds to the SSE.
And no, I won’t steal the recent excellent reference to “Oklahoma!” used by According to Pliny, though I certainly think isobar curtains would be interesting… 