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It wasn’t that long ago that Warren Buffett gave a “clear skies” proclamation for the airline industry after his portfolio managers took stakes in all the major air carriers. But that was then, and a lot has happened since. Now Delta Air Lines Inc. (NYSE: DAL) is adding some extra concern about the airlines. Delta shares had been down about 15% after its earnings report in July, and now the more recent bounce in shares may have some headwinds.

Delta issued its August flight metrics, but it lowered its own third-quarter unit revenue metrics and operating margin guidance. Delta’s release showed that it now expects passenger unit revenue growth to be only about 2.0% to 3.0% rather than a prior forecast of 2.5% to 4.5%. The airline noted that the recovery in domestic close-in yields has been slower than anticipated.

Delta also disclosed that its all-in fuel price for the third quarter should now expected to be in the range of $1.68 to $1.73. This is a higher projection that previously offered up, and it was said to be driven by the increase in market prices that began in late July.

Delta now expects that its normalized cost per available seat mile excluding fuel will be up approximately 2.0%. Its operating margin was also put in a range of 16.5% to 17.5%, lower than its prior guidance of 18.0% to 20.0%. Delta said that higher fuel prices and close-in yield softness combined resulted in the two points of margin pressure for the quarter.

Delta may have done a good job managing its other expenses so far, but its shares were last seen down 1.4% at $46.82. Its 52-week trading range is $36.59 to $55.75. Other airline softness was seen elsewhere, and there remains an ongoing concern about airline ticket prices if more fare wars take place.

American Airlines Group Inc. (NASDAQ: AAL) was down 0.9% at $44.90, in a 52-week range of $33.90 to $54.48.

JetBlue Airways Corp. (NASDAQ: JBLU) was last seen down 0.8% at $19.67, and its 52-week range is $15.77 to $24.13.

Southwest Airlines Co. (NYSE: LUV) was last seen down 1.1% at $51.59. Its 52-week range is $36.31 to $64.39.

United Continental Holdings Inc. (NYSE: UAL) actually was trading up 0.4% at $62.68 on Tuesday morning, but its shares had been higher ahead of Hurricane Harvey shutting down its mega-hub in Houston. United Continental’s 52-week range is $49.28 to $83.04.

Here was the value of Warren Buffett’s airline stakes at the end of the second quarter of 2017. He still held close to $2.0 billion in American Airlines shares, more than $2.5 billion in Delta shares, almost $3.0 billion Southwest shares and over $2.1 billion in United Continental.

Airline stocks can be more than turbulent around various aspects of each business cycle. Hurricane Harvey took out days worth of flights in Houston, and now we have Hurricane Irma that may impact multiple flight locations in major metro areas in Florida and elsewhere around the Gulf of Mexico or eastern United States.