Rising inventory levels are weighing on natural gas exchange traded funds, but a growing tropical system in the Gulf and colder weather over central U.S. helped curb losses.

The United States Natural Gas Fund (NYSEArca: UNG) was 0.4% lower Thursday. UNG is down 3.6% year-to-date.

Natural gas futures were down 0.1% Thursday, trading around $3.54 per million British thermal units.

According to the U.S. Energy Information Administration, natural gas stockpiles for the week ended Sept. 27 rose 101 billion cubic feet , above market expectations of an increase in the mid-90 bcf range.

In comparison, inventories rose 77 bcf in the same week year-over-year, and the five-year average for the week was a 82 bcf injection.

U.S. natural gas stores now stand at 3.487 trillion cubic feet, or 155 bcf less year-over-year, but 49 bcf above its five-year average.

Meteorologists forecast colder weather and even snow over the central U.S., Investing reports. Demand for natural gas rises as homes and businesses use gas heating in cold weather.

The growing Tropical Storm Karen in the Gulf of Mexico is expected to reach hurricane strength and hit landfall later this week. Tropical systems disrupt gas production in offshore rigs in the Gulf, which is home to about 10% of U.S. natural gas production.

United States Natural Gas Fund

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Max Chen contributed to this article.