台風 and 暴風: story, path map, and return because a storm was expected
Compare a 台風 approaching in a story and its path map read in class with 暴風 shaking a tree or being expected. Separate the named phenomenon and context from the boat's completed return.
A typhoon in a story and a class
台風（たいふう） means typhoon. 「物語では大きな台風が島に近づいてくる。」（In the story, a large typhoon approaches the island.） 物語では establishes the story context, and 近づいてくる describes movement toward the island. This is not a report of a typhoon currently observed in the real world.
「防災の授業で台風の進路図を読み取った。」（In disaster-prevention class, we read a map of a typhoon's path.） The object read is a typhoon path map. 防災の授業で establishes the class context, and 読み取った describes reading that material rather than making new observations of an actual path.
A storm's effect and a storm expected
暴風（ぼうふう） means storm. 「暴風で庭の古い木が大きく揺れた。」（The old tree in the garden swayed violently in the storm.） 暴風で identifies the cause of the tree's violent swaying. The tree's movement is a stated result.
「暴風が予想されたため、船は港に戻った。」（A storm was expected, so the boat returned to port.） 予想された describes the storm being expected, while 戻った reports the boat's return. Returning because a storm was expected does not report that the boat was caught in an actual storm.
Reading the names within their contexts
The 台風 examples concern an approach in a story and reading a map in class. The 暴風 examples concern a tree swaying and a boat returning because of an expectation. Read the phenomenon names together with 物語, 授業, and 予想.
These examples give no wind-speed thresholds for distinguishing the names. Follow the story's movement, reading the map, the tree's change, and the boat's reason for returning without collapsing every strong wind into the same phenomenon.
In 「暴風が予想されたため、船は港に戻った。」, what was expected, and what completed action is reported?
Show the answer and why
The storm was expected; the boat's return to port is the completed action. The sentence supplies neither a boat being caught in an actual storm nor a numerical wind-speed category.