harete iru uti ni, suupaa he dekakemasu.

〜うちに means while ... is the case, during the time that ..., or before ... changes.

So 晴れているうちに means:

• while it’s sunny
• while the weather is still good
• before it stops being sunny

In this sentence, the speaker is saying they will go to the supermarket while the weather is nice, presumably before rain or bad weather starts.

This is a very common question.

晴れる means to clear up / to become sunny.
晴れている describes the current state: it is sunny / the sky is clear.

So:

• 晴れる = it becomes sunny
• 晴れている = it is sunny
• 晴れた = it became sunny / it was sunny

Because うちに here refers to the period during which it is sunny, 晴れている is the natural choice.

In 〜うちに, the に is part of the grammar pattern itself. You should learn うちに as one set expression.

It marks the time frame in which something happens:

• 若いうちに = while you are young
• 熱いうちに = while it is hot
• 晴れているうちに = while it is sunny

So this is not a separate に you need to analyze word by word every time; it is part of the established pattern.

They are similar, but not exactly the same.

• 〜間に focuses more on during a span of time
• 〜うちに often has the feeling of before the situation changes

In this sentence, 晴れているうちに strongly suggests:

• it is sunny now
• it may not stay sunny
• so I’ll go before that changes

That “before it changes” nuance is why うちに fits very well here.

へ marks direction: to / toward.

So:

• スーパーへ出かけます = go out to the supermarket

You could also often hear スーパーに出かけます, and in many contexts へ and に are both possible for destinations.

The nuance is:

• へ emphasizes direction toward
• に emphasizes arrival/destination

In everyday speech, the difference is often small.

出かけます means to go out, to head out, or to leave for somewhere.

So スーパーへ出かけます is not just a neutral I go to the supermarket. It has the sense of:

• I’m heading out to the supermarket
• I’ll go out to the supermarket

It often implies leaving home or your current place.

Japanese very often omits the subject when it is clear from context.

So even though English would usually say:

• I’ll go to the supermarket while it’s sunny

Japanese simply says:

• 晴れているうちに、スーパーへ出かけます。

The subject is understood from the situation. It is probably I, but Japanese does not need to say it unless necessary.

The verb 晴れる originally has the sense of clearing up. For weather, it means to become sunny / to clear.

So 晴れている literally comes from that verb, but in normal usage for weather it is best understood as:

• it is sunny
• the weather is clear

So yes, there is a “cleared-up sky” idea behind it, but in practice it is just the standard way to describe sunny weather.

The comma after 晴れているうちに separates the time phrase from the main action:

• 晴れているうちに、 = while it’s sunny,
• スーパーへ出かけます。 = I’ll go out to the supermarket.

It makes the sentence easier to read. In Japanese, commas are often used flexibly, so this comma is natural but not always absolutely required.

Yes, a little.

Because 〜うちに often means before the situation changes, the sentence can suggest:

• it’s sunny now
• maybe it won’t stay sunny
• so I should go now

That does not mean strong emergency-level urgency, but it does give a feeling of better do it while I have the chance.

Yes. That is a very natural way to bring out the nuance.

Possible translations include:

• I’ll go to the supermarket while it’s sunny.
• I’ll go to the supermarket while the weather is still nice.
• I’ll go to the supermarket before it stops being sunny.

The exact English wording depends on how directly you want to show the nuance of うちに.

Because スーパー is a loanword, from supermarket.

In Japanese, foreign loanwords are usually written in katakana.
Here, スーパー is a shortened form of スーパーマーケット.

So:

• スーパーマーケット = supermarket
• スーパー = supermarket / grocery store

The shortened form is very common in everyday Japanese.