Hurricane Sandy in the US led to more than 200 flight cancellations and a drop in passengers using Heathrow last month.
This and the late school half term holiday led to a 0.1% decline is passengers using the airport to 6 million in October over the same month last year.
Without these two events, passengers for October would have been up by 1.7%, according to the airport.
Many passengers affected by Sandy are expected to have rebooked onto flights this month.
Overall passengers to North America were up 0.3% compared with October 2011.
European passenger traffic was up 0.9% overall with a 4.5% rise to Germany, but fell 9.6% to Greece, 7.3% to France and 2.3% to Italy.
Of the Bric economies, passenger numbers were up 5.7% to Brazil, 2.9% to Russia and 4.3% to China, but down 7.3% to India, due to airlines reducing or ceasing services.
Customer satisfaction scores have continued to improve at Heathrow.
Latest results from the independent benchmarking programme run by Airports Council International gave Heathrow its best ever score in the third quarter with 75% of passengers rating their experience at the airport as either ‘excellent’ or ‘very good’.
Heathrow chief executive Colin Matthews, said: “We are delighted to report record customer satisfaction scores.
“We are determined to keep on improving Heathrow for passengers and are investing £20 million every week in new facilities.”