Yep. If it was a general sentence you make the subject have a definite article:
الصيف حار في عمان (THE summer is hot in Oman).
If you want to note only a specific summer you would need to add a marker like (this: هذا) for example to make the sentence under the same structure:
هذا صيف حار في عمان (THIS is a hot summer in Oman).
You can also put a definite article and the meaning would change to (THIS SUMMER is hot in Oman)
هذا الصيف حار في عمان - .
maybe not much sense in meaning but just to get the idea through