∠ FBC = 30 (known)
∠ABC=60
∠A=30
AB = 2bd (the right-angled side opposite to the 30-degree angle is half of the hypotenuse)
AB=220BD= 1 10? Ad = 1 10√3 with Pythagorean theorem
12-110 √ 3/20 < 4, so it will not be affected by typhoon.