Translation:Did you see the weather forecast?
There is also a present perfect tense in Irish, but it’s not used in as many situations as it is in English; unlike the English present perfect, which can be used for any completed event with present relevance no matter how long ago that event was completed, the Irish present perfect is only used for a completed event with present relevance that has recently completed. Thus, the Irish present perfect An bhfuil tú tar éis réamhaisnéis na haimsire a fheiceáil? would be translated into English as “Have you just seen the weather forecast?”. Since this exercise is in the Irish past tense, it could be translated by either the English simple past “Did you see the weather forecast?”, or by the English present perfect “Have you seen the weather forecast?” if the questioner is not concerned with how recently you’d seen it. Since this exercise is without context, both of these English forms should be accepted.
"have you seen?" is in what's called the "present perfect tense" (even though it refers to something in the past). The simple past in Irish (an bhfaca tú?) is often used to translate the present perfect in English into Irish, but when translating from Irish to English, you're usually better off translating the simple past to the simple past ("did you see?").
In short, "Did you see?" and "Have you seen?" are both translated into Irish as an bhfaca tú?. But when translating in the other direction, "Did you see?" is the "default" translation - you would only translate it into the present perfect if the context made that a better translation.
So "Have you seen the weather forecast?" isn't necessarily wrong, it's just not the best translation.
The definite article placed between the nouns in the genitive is roughly equivalent to "the something of the something" in English.
Réamhaisnéis na haimsire = the forecast of the weather.
An réamhaisnéis aimsire = the forecast of weather.
Réamhaisnéis aimsire = a forecast of weather.
You would almost always refer to "the weather"/"an aimsir" in Irish when using the nominative and this is preserved when putting it into the genitive by using "na haimsire".