New October retail sales data out this morning suggests that the fourth quarter could be off to a rocky start for e-commerce.

Growth in U.S. retail sales that take place outside of stores, known as nonstore sales, decelerated in October, with sales dropping 0.3% compared with September 2017, according to the U.S. Commerce Department.

Adjusted for seasonality, nonstore sales reached $52.14 billion in October, a 6.8% increase compared with $48.82 billion in October 2016. That’s a smaller gain than September, which experienced a 9.2% year-over-year increase, and August, during which nonstore sales grew 8.4% compared to prior year period.

Nonstore sales mainly take place online but also include other channels such as mail and telephone orders, door-to-door sales and sales through vending machines.

Internet Retailer uses the monthly nonstore figures disclosed by the Commerce Department as an early indicator of the health of the e-commerce market. The Commerce Department only reports e-commerce sales on a quarterly basis. The agency will release third quarter results on Friday, November 17.

A historical look at the correlation between nonstore sales and e-commerce sales shows that e-commerce is a growing portion of these sales. In the second quarter of 2017, for example, the latest quarter for which data is available, e-commerce represented 72.5% of nonstore sales, Internet Retailer analysis shows. That compares with 68.8% in the second quarter of 2016.

Using those same percentages, this would suggest that in October, e-commerce sales reached roughly $37.80 billion, a 12.5% increase from $33.59 billion in October of last year.

This is vastly different from retail sales that occurred in stores in October. When factoring out the sale of automobiles, fuel and transactions in restaurants, retail sales that occurred in stores reached $244.00 billion in October, a 3.4% increase compared with $235.94 billion in October 2016.

Still, the roughly 12.5% increase in e-commerce sales in October would be much lower than recent months.

During the second quarter, for example, online sales reached $105.10 billion, a 16.3% jump compared with $90.40 billion in the second quarter of 2016. That was the highest year-over-year increase in online retail sales since the first quarter of 2012, when e-commerce sales increased 16.8% over the prior-year quarter.

Still, the bulk of online sales transactions in the crucial fourth quarter occur in November and December, and there are multiple indications that the online holiday shopping season is off to a good start.

Adobe Systems Inc. reports that each day from Nov. 1 to Nov. 11 this year drew more than $1 billion in online sales, resulting in the firm upping its forecast for web sales during November and December by 1.8%. Based on online sales Adobe has tracked so far, U.S. shoppers are on pace to spend $109.3 billion in those two months, a 15.8% increase compared to the same period last year.