August was a very good month for Detroit, as the Motor City automakers all posted impressive double-digit gains even while consumers were spooked by a whipsawed stock market and falling consumer confidence.

Toyota and Honda sales were down, both companies still seeing vehicle shortages stemming from last March's Earthquake in Japan. But Nissan, which jacked up incentives in August and resumed its supply sooner than its rivals, posted a 23% gain on the month.

The industry as a whole posted a healthy 8% gain. But, auto industry analysts have warned that the second half of this year would see a dropoff in auto sales, compared with the first half. The wobbling U.S. economy is still leaving a lot of would-be buyers on the sidelines.

Hurricane Irene was blamed for some loss of sales in August, but not that many. GM, for example, said it reckoned it only lost about 1,000 sales nationwide. Nissan said the storm cost it about 3,300 sales because its dealerships are over represented in the Northeast.

Small cars are surging

GM sold 20,000 Chevy Cruze sedans, it's all-new compact sedan. Ford sold more than 20,000 Fiesta and Focus compact and sub-compact sedans with no help from sales incentives.

A few factors are driving small-car sales for MoTown. Small cars are still in short supply from Honda and Toyota, and consumers who have been in the market for new cars are trading down to less expensive, more fuel efficient models.

General Motors sales were up 18% in August, with healthy gains for GMC, Buick and Chevy. GM's sales and financial performance have been strong this year, buttressing the case for GM's new management. But the share price of the automaker continues to languish, off about one-third from its IPO price ten months ago.

Chrysler continues to impress, posting better than 20% sales gains in each of the last four months despite not having a raft of new models to sell.

Luxury brand sales surged, supporting the argument that those who have jobs and money are willing to spend it. BMW sales were up 15%, while Mercedes-Benz was up 9% and Porsche was up 30%. Lexus, Infiniti and Acura were down, also impacted by a shortage of vehicles due to last March's Hurricane rather than a falloff in consumer demand.