"On the one hand, business capital spending is not enough to push GDP faster than 3 percent currently, but 2 percent GDP growth will be fast enough if it continues to bring down unemployment," Rupkey wrote.
Joseph LaVorgna, chief U.S. economist at Deutsche Bank, said durable goods will tell part of the story on capital spending, but he is looking to industrial production and trade data for a better read of its impact on economic growth.
"My guess is the core of the report, the core durables is going to be better than people think," he said. "Durable goods are one of the many pieces we use to estimate capital spending, but they're not the most important. … Even if for some reason they would be disappointing, that would still not change my expectation that the fourth quarter is doing well."
Consumers are being put to the test this week, with the holiday shopping season extending into the post-Christmas period Thursday and through next weekend.
ShopperTrak reported that retail sales at general merchandisers in the week Dec. 15 to 22 was down 3.1 percent from the same week last year. It also said retail brick-and-mortar shopper traffic dropped by 21.2 percent year over year.
"I think it's disappointing," said Bill Martin, founder of ShopperTrak. "I think it's that November has stolen a lot of business from December. November was up 3.4 percent, which was a little bit stronger than we had anticipated. ... The Black Friday and Thanksgiving Day sales took a lot of energy out of the consumer."
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ComScore will release fresh data showing the results of online shopping Thursday. But Martin says he thinks the consumer slowed in December and that the decline in shopping at physical stores was not just the impact of online spending.
Rupkey said some of the consumer momentum could slow down in December.
"The way the data goes is it's red hot for a couple of months, and then it slows down. It almost doesn't bode well for December sales," he said.
ComScore said Wednesday that online sales in the week earlier eclipsed $1 billion for each of the five workdays for the first time. That helped boost total online spending by 21 percent so far this year, when comparing the days since Thanksgiving to the same period last year. It also said growth is coming from weekend spending, which has typically been slower for online retail.
But there's still time for shoppers to head out to the mall and other retail destinations, Martin said.
"We still have some days left to go. There could be some ground made up. Today was an important day, one of the top five days of the year," he said, adding that Dec. 26 is the seventh busiest.
Gift card sales are up, and those could be used in the weekend following Christmas, also potentially important days for this shopping season.
"We're still looking at 2.4 percent [gain] for the holiday season, even though we're seeing some softness in December," Martin said.
Retailers have been using a lot of promotions and discounting.
"We think they're doing everything they can to make sure their shelves are empty," Martin said. "There's a bit of the retailer blinking in this cat and mouse game, with the deeper discounts we've seen. And I suspect we're going to see more discounts rolling through next week, post-holiday."
Still, this should be the biggest holiday season ever, with an estimated $265 billion in sales. Last year was the largest year on record, eclipsing 2007.
"The stock market is setting records. Retail is setting records, but I think a lot of early promotions, a lot of strength in November is just weakening the whole December outlook," he said.
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ShopperTrak also said that despite more markdowns and promotional efforts, "Super Saturday" (Dec. 21) sales were down by 0.7 percent from 2012.
In-store shopper traffic fell 18.1 percent from the same day last year.
—By CNBC's Patti Domm. Follow here on Twitter