I can't believe it has rained for the last 4 days.
You can specify from which date or day it has been raining. Then you can be more precise. For example if today is Friday, you could say "It has been raining since Tuesday and it's still raining!" or "It has been raining all week!"
If it has been rain heavily you can say "it is raining cats and dogs!" This is an old English expression. It is believed that a while ago (100 odd years) cats and dogs would hide in the roof where it was warm. When it rained heavily they would fall out... Hence the saying "It has been raining cats and dogs all week!"
When you express disbelief, like in this sentence "I can't believe...." it tells the listener that it is unusual that it has "rained for the last 4 days."
例：It has been raining all week.
「今週ずっと[雨が降っている](https://eikaiwa.dmm.com/uknow/questions/71967/)。」
例：It is really coming down.
「本当にずっと雨が降っている。」
例：I can't believe it has rained for the last 4 days.
「もう4日も雨が[続いている](https://eikaiwa.dmm.com/uknow/questions/71593/)なんて信じられない。」
いつから雨が降っているかを加えることで、もっと正確に表現できます。
例えば、"It has been raining since Tuesday and it's still raining!"「火曜日からずっと雨が降り続いている」か例文の1といいましょう。
強い雨が降り続いている場合、"it is raining cats and dogs!"「[どしゃぶり](https://eikaiwa.dmm.com/uknow/questions/391/)だ！」ということもできます。
これは古いイギリスの表現で、暑い時は犬や猫は隠れており、雨が降ると涼みに飛び出すことからきています。
"I can't believe..."「〜なんて信じられない」は、強調したい時に使えます。相手に平凡な出来事ではないことを伝えるのにいいですね。
"It has been raining for days" This is an English phrase used to explain that it has been raining for a long time.
"It has been raining since yesterday morning." This explains that it started raining yesterday morning and has continued through till now.
"It has been raining for days"
（ずっと雨続きです）
これは長い間、雨が続いていることを説明する英語の表現です。
"It has been raining since yesterday morning."
（昨日の朝から雨が降り続いています）
これは昨日の朝降り始めた雨が今もまだ降り続いている、と言う事を説明しています。
Explanation: Use 'since' when you want to talk about the intervening period between a fixed point in the past and the present time. The present perfect or present perfect continuous are the most common forms used with 'since.'
Example sentence:
"I've been riding bikes since I was 10 years old."
解説：ある時点から過去または現在の次の時点までの間隔について表現したい場合は 'since' という言葉がつかえます。現在完了形または現在完了進行形で使われる最も一般的な言葉が、 'since.'です。
例文：
"I've been riding bikes since I was 10 years old."
（10歳の時からずっと自転車に乗っています。）
Here is a list of sentences you can say about rain that won't stop.
persistent - The rain is so persistent.
continues - It continues to rain every day.
never-ending - The rain seems like it's never ending.
incessant - This incessant rain is driving me crazy. It won't let up.
unceasing - The rain is unceasing. Every day I need my umbrella.
endless - The endless rain is making all the roads muddy.
relentless - The rain is relentless.
雨が降り続いてやまない事を表す文のリストです。
persistent
- The rain is so persistent.
（この雨はしつこい）
continues
- It continues to rain every day.
（雨が毎日降り続いている）
never-ending
- The rain seems like it's never ending.
（この雨は果てしなく降り続くみたい）
incessant
- This incessant rain is driving me crazy. It won't let up.
（この雨のおかげで狂いそうだ、全然やまない）
unceasing
- The rain is unceasing. Every day I need my umbrella.
（ずっと雨が降っているから、毎日傘が要ります）
endless
- The endless rain is making all the roads muddy.
（ずっと雨が降っているから道が泥だらけです）
relentless
- The rain is relentless.
（この雨はしつこい）
When it rains from morning until late in the day, then you can say that it has been raining all/throughout the day.
For example, you can say:
-It's been raining all day. I am annoyed.
朝から夜遅くまで雨が降っているなら：
"It has been raining all/throughout the day"
（一日中雨が降っています）
と言えます。
例えば、次のように言うことが出来ます。
【例文】
-It's been raining all day. I am annoyed.
（一日中雨が降っています、イライラします）
The two sentences provided above have the adjectives continuous and non-stop. Although these words can be used in different ways in these two sentences they mean constant or without interruption. These two words are common in both formal and informal settings, so they would make a great addition to your vocabulary!
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