唔用 unusually ，用 unusual ，又得唔得呢

The weather has been unusually cold for the time of the year.

應該用 unusually (adverb) = 特別地, 異常地
用來 modifies 個 adjective (cold),
cold 在這句子作 adjective, 不是作 noun
unusually cold = 異常地寒冷

The weather has been unusual for the time of the year.
unusual (adjective) = 不尋常, 罕見的
unusual 用來形容天氣 (weather)

The weather has been unusual and cold for the time of the year.
兩個 adjectives (unusual 與 cold) 同時形容天氣

adjective 與 adverb 有不同的功能 (function)
adjective 只形容 noun, pronoun
adverb 修飾 verb, adjective 或者 another adverb
小心 hard, hardly, late, lately, fine, finely, round, roundly, early, daily ... etc 這些字

如果形容天氣相當不尋常和出人意料地寒冷, 我會這麼寫
The weather has been quite unusual, surprisingly cold for the time of the year.

quite 和 surprisingly 都是 adverb

題外
has been + past participle ~ to form passive voice (present perfect tense)
has been + present participle ~ to form present perfect continuous tense (active voice)

has been 可以作 linking verb
has been + adjective/adjective phrase
has been + noun/noun phrase (e.g. He has been a good student.)

has been 後面要跟pp
唔可以咁用

unusual糸adjective,usually糸adverb