Learn Turkish: Uzmanlar, kasırganın daha şiddetli olacağını haber veriyorlar. - Experts inform that the hurricane will be more severe.

It uses the future object participle taught in this lesson. Start with olmak (to be) and add the future suffix -acak, which softens to -acağ- because a vowel comes next. Then add -ı (3rd person singular possessive, linked to the hurricane), the buffer letter -n-, and finally the accusative case -ı because the whole clause is the direct object of the main verb.

Why is it kasırganın (genitive) instead of just kasırga?

In Turkish complement clauses, the subject of the inner clause acts like a possessor. The sentence literally translates to something like 'Experts are giving news of the hurricane's future being more severe.' So, kasırga takes the genitive suffix -nın to pair with the possessive suffix on olacağını.

Why does olacağını have the accusative case suffix at the end?

The entire clause kasırganın daha şiddetli olacağını acts as the specific direct object of the compound verb haber vermek (to give news / to inform). Because they are giving news about a specific thing, the clause needs the accusative marker -ı.

Since Uzmanlar (experts) is plural, is the -lar on haber veriyorlar mandatory?

No, it is optional. In Turkish, when a human subject is plural, the plural suffix on the verb can be dropped. Saying Uzmanlar ... haber veriyor is also completely natural and correct.