Need advise on August end travel

Hi Everyone Xin chào

I have planned to visit Vietnam in the last week of August and wanted to know if it will be safe to visit Ninh Binh, Ha Long Bay and Sapa considering the monsoon and rain for day trip cruise tour ?

Dates- 27-30th August and looking for a day trip.

Also could you advise on best offline store for samsung mobile/iphones in Ho Chi Minh city ?

Thanks