It is monsoon time in the month of September and October in Spiti, though not in full swing. Till august rains poured do cause havoc to the roads in September and October. You need to double check which route is safe. Water flow is seen in the road. However both these months are ideal time to travel for you get to view after rain nature. So it is an ideal time to travel provided you keep checking about the routes, weather till the date of travel and then plan your journey.
Hi Pankkaj, Spiti is a dry cold desert area that sees close to no rain . Spiti even in the monsoon time sees almost no rain.
But to reach Spiti you have to pass the Kinnaur roads which are very highly see landslides during the monsoon. So before starting your trip please check the weather condition of the places you travel to reach Spiti or Kaza . It is safe to travel in Spiti even in the monsoon What you just need to take care is the way you will pass to reach Spiti.