This is one of the verses telling us that knowledge of what is to unfold in the future is something that Allah has reserved to Himself. It is, in other words, part of the Unseen.
Allah also says: " Say (O Muhammad): No one in the heavens and the earth knows the Unseen but Allah; and they know not when they will be raised (again)." [Sûrah al-Naml: 65]
This does not mean people cannot make informed judgments about what to expect from the data available at present. That has nothing to do with the Unseen. Such predictions and estimates may or may not come to pass.
This is the type of information that meteorologists work with when they give a weather forecast. When a meteorologist says that it is going to rain tomorrow, she relies on measurements of current weather conditions and images of cloud movements. With this information, they can say with reasonable certainty that a rainstorm is coming to a particular locality.
This kind of prediction is not part of the Unseen, since it is based on empirical data. The forecast is merely a deduction from what is being observed in the physical world. That which is grounded in observation is – by definition – not part of the Unseen, since the Unseen is that which cannot be ascertained through observation and experience.
Though the weather forecast for the week requires complex analysis and sensitive instruments, it si no different than the commonsense predictions and judgments that we make every day. If you drop an egg from the roof of a building, you can safely predict that it will crack and splatter on the pavement below. It has not happened yet, but present conditions and past experience give you enough information to make an accurate forecast.
The same can be said for weather forecasts, though they require satellite imagery and careful measurements. It is merely a difference in complexity. Knowledge of the Unseen does not come by way of sensitive instruments and calculations. The only access human being have to knowledge of the Unseen is prophecy, and that was reserved for the prophets (peace be upon them all).
Still, it behooves a meteorologist, doctor, or other specialist who speaks about the future on the basis of empirical evidence, to keep in mind that what she predicts does not necessarily have to come to pass. It does not matter how much evidence there is for the forecast or how certain it might seem. The matter still rests ultimately with Allah's will. Whatever Allah wills to happen will come to pass, and whatever He wills not to happen will never be.
Allah says: " And in the heaven is your providence and that which you are promised;." [Sûrah al-Dhâriyât: 22]
Allah is telling us that our worldly and spiritual sustenance – the rains and everything else – is determined by His will.
And Allah knows best.