As if commodity markets needed any more drama this year, this year's Atlantic hurricane season could be the seventh consecutive with above-average activity, raising risks for U.S. grain exports as well as oil production and refining capacity.

Significant disruptions for U.S. commodities resulting from hurricanes are more the exception than the rule. But tight global stocks, high prices and geopolitical conflicts could amplify any storm effects that surface this year.

Present for a third consecutive year, La Niña is the primary culprit for forecasters' beefier predictions for hurricane season, which tends to peak in the second week of September.

La Niña-induced droughts have already contributed to higher global grain prices, wrecking soybeans and corn in South America over the last two seasons and whittling this year's U.S. hard red winter wheat crop to a 59-year low.

Unfortunately for commodity markets, the Gulf of Mexico is a common destination for Atlantic hurricanes. Louisiana ports are the busiest for U.S. grain exports, and about half of U.S. petroleum refining capacity resides along the Gulf Coast.

In August 2017, Harvey made landfall in Texas as a major hurricane, knocking up to 23% of U.S. refining capacity offline at one point. U.S. gasoline futures surged as much as 30% in the days following landfall, though the resulting prices were still only half of today's record levels.

Four years later, Hurricane Ida damaged or destroyed several Louisiana grain export terminals, capping September U.S. corn and soybean exports at just half the typical volume.

Strong grain exports returned in October and gasoline futures corrected within days of Harvey's 2017 arrival, though there may be less room for error today. Global grain shipments are already precarious with Ukraine's offerings still very limited.

U.S. distillate fuel oil stocks have dropped to more than 15-year lows and record lows along the East Coast, which relies on supplies from the Gulf. Low stocks in Europe and pressures from sanctions on Russia may not be able to help pad U.S. supplies in case of a hurricane-fueled shortage.

Sometimes hurricanes can benefit agriculture, as in 2012 when storm remnants dumped rain on drought-withered soybeans in the eastern United States. But impacts are usually negative, frequently hampering grain and feed transportation, livestock operations and cotton production.

The U.S. National Oceanic Atmospheric Administration last month placed 65% odds on an above-average Atlantic hurricane season including six to 10 hurricanes, between three and six of them considered major. NOAA had 60% confidence for above-normal activity ahead of the 2021 and 2020 cycles.

Braun is a market analyst for Reuters.