Investors in the gambling business have enough worries, from the recession to balance-sheet balancing acts to disappointments in Las Vegas and Macau.

So in honor of the Atlantic hurricane season -- June through November -- and Macau typhoon season -- April to October -- let me offer another investment warning, especially for those with short-term horizons. Acts of God can affect casino stocks just as sharply as better-known risk factors.

Case in point ...
The most extreme example was Hurricane Katrina, which crushed the Mississippi casino industry in August 2005. Some casinos reopened after being repaired or rebuilt; others stayed closed for good.

For example, it took Penn National Gaming (NASDAQ:PENN) 10 months to reopen one casino, and 12 months to reopen another. The company says community damage after horrific storms hurt operations because travel and staffing were affected.

Less violent storms and floods can tilt quarterly revenue and earnings, too. Casinos have insurance, but companies warn investors that claims payments can take a long time. Policies may not cover all losses, and insurance has become more expensive and/or harder to obtain.

Hurricanes, floods, typhoons, blizzards
Companies most vulnerable to natural disasters have prominent portfolios of riverboat, dockside and/or seacoast casinos. In addition to Penn National Gaming, they include Isle of Capri Casinos, Pinnacle Entertainment (NYSE:PNK), Ameristar Casinos (NASDAQ:ASCA), and Boyd Gaming (NYSE:BYD).

Macau typhoons could have an impact on Las Vegas Sands (NYSE:LVS), MGM Mirage (NYSE:MGM), Wynn Resorts (NASDAQ:WYNN), and Melco Crown Entertainment (Nasdaq; MPEL).

Isle of Capri, which also warns that blizzards could affect its Colorado properties, says that although business interruption insurance has provided adequate coverage, the company can't guarantee that future claims will provide "sufficient" payment for damages.

Beware of insurance fine print
Let's take one casino company as an example.

Hurricane Katrina destroyed a Pinnacle Entertainment casino in Mississippi and forced a New Orleans casino to close for 34 days. Hurricane Rita knocked out a Louisiana casino for 16 days. Last year, Hurricanes Gustav and Ike affected a Louisiana casino, and flooding caused the temporary closing of a St. Louis casino on the Mississippi River. This casino has experienced "growing losses" due in part to flood-related closings. Pinnacle is determining if it can relocate the casino.

The company's latest 10-K statement recounts the damage, giving investors a lesson in storm insurance. In 2006, Pinnacle sued three insurers over claims for a Biloxi, Miss. casino that was closed after Hurricane Katrina; the property was later sold. At that point, $192 million in claims had been paid, but Pinnacle was still fighting one insurer in court.

Obtaining insurance has been more difficult since Hurricane Katrina, Pinnacle says. Some companies have stopped writing policies for hurricane damage in Mississippi and Louisiana. Others have raised premiums and limited coverage. Stating that the recession has created "uncertainty" about the "viability" of certain insurance carriers, Pinnacle warns investors about the perfect storm (pardon the pun) of more violent weather and diminished coverage.

Conduct extra research
Studying stocks requires knowing numbers and learning industry trends, but investors in weather-sensitive companies must expect the unexpected as well.

For example, storms can create a reverse effect on a company's performance. Isle of Capri's revenue from casinos in Natchez, Miss. and Lake Charles, La. dropped in recent periods, compared with the stronger business that followed Hurricane Katrina's damage to Gulf Coast casinos. When gamblers returned to the Gulf Coast, Natchez took a hit. At Lake Charles, customers returned to competing casinos that had been closed after being damaged by Hurricane Rita.

I doubt that prospective investors with a long time horizon will constantly check the website of the National Oceanic and Atmospheric Administration before they take a chance on a casino company. But I'm willing to bet that day-traders and short-sellers will consult The Weather Channel or a private forecasting service before investing in -- or against -- a casino company that has many properties in areas subject to natural disasters.

That scenario's not far-fetched. CME Group, the big marketplace for derivatives, offers weather futures and options on 42 cities worldwide as well as future and options on hurricanes in the eastern U.S.

Investors can't guard against every risk factor. Still, as the casino companies' storm experience illustrates, investors doing their homework should also look to the skies -- if only to check the weather -- when estimating risks.

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Fool contributor Robert Steyer doesn't own shares of any companies cited in this story. Ameristar Casinos is a Motley Fool Hidden Gems selection. The Fool's disclosure policy never bets against anyone/thing with the capacity to smite.