October is partly in the wet season but my experience of over 15 years going here it is not guaranteed. In fact a rainy day on Ha Long Bay only enhances the experience but I would only do an overnight

. As far as Hoi An, it is also not a given that you will be flooded out. I suggest you have a look at long distance weather forecasts which are pretty good (Surf Forecast.com is good ) as this will give you the opportunity of having a plan B to go further south if things get cranky.

Cheers Ross

Most of the "trouble" with the rainy season up along the coast is that the sun lovers often miss out. It may not rain, but it will often be overcast.

So if you spend a thousand bucks on airfare in the hope of establishing a solid foundation for skin cancer on a sandy beach then I think the south is a safer bet.

Thanks and how would u compare SAPA to Pu Luong? Which one is better

What's "best" is subjective.

In any event this is why you should always try to keep a flexible itinerary in Vietnam:

https://e.vnexpress.net/news/news/streets-flooded-trees-felled-as-afternoon-rains-barrel-down-sa-pa-hanoi-4513829.html

Thanks for sharing

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With 6 days I suggest that you stick to 1 region because traveling around in Vietnam takes time. In Hanoi, stay in the old quarters for easy walking to historic places and restaurants. I chose Ninh Binh because it is less touristy and yet still has the karst mountain and river boat rides. Loved cycling around the area. Originally I planned to go to Sapa to hike but when I heard about the mudslides caused by the rain, I changed my plan to Mai Chau and Pu Luong Nature Reserve instead. Sapa's weather is unpredictable so check before you go.

For more info and photos, see https://bigsmallmoment.wordpress.com

as we have 6 days only we want to book halong tour first--we arrive late night and next day morning we are planning to do the Halong Bay trip. Based on your experiences would u recommend that?

We want to do city tour at the end as we may want to shop as well and we have limited time.

What would u recommend.

Only my opinion, but as you have such a limited time for your trip, it might be a good idea to avoid wasting a night on Cat Ba island. I found it underwhelming. However, the trip on Halong Bay with an overnight on board was wonderful.