Air traffic through the Houston Airport System showed a 4% decrease in September to 4.6 million. Domestic traffic brought in just over 3.7 million passengers, down nearly 5% and international traffic showed a 1-point decline, bringing in approximately 910,000 passengers.
Year to date, the passenger count through the airport system has reached almost 45.5 million, down 2% YOY. Domestic traffic has decreased by just over 1%, to 35.8 million, while international passengers have dipped by almost 3% to 9.7 million. 

Air Traffic – By the Numbers
Hobby Airport welcomed just over 1 million visitors in September, a 3.4% dip compared to the same time last year. The majority of passengers out of Hobby were domestic flying Southwest, at nearly 960,000, a 94% domestic share. International traffic represented a significantly smaller portion of total traffic, bringing in nearly 52,000, up almost 1% YOY. 
Bush Intercontinental Airport (IAH) welcomed approximately 3.5 million visitors, down about 4%, with domestic traffic making up about 2.7 million, a 5-point drop, and international visitors making up the remaining 858,000, down 1%. 
United Airlines maintained a consistent share of total passengers through the Houston Airport System compared to last month, at 58%, with Southwest Airlines taking the second largest share at 22%. 

See full stats here.