Natural gas exchange traded funds weakened Thursday on mild temperature forecasts, brushing off an unexpectedly low natural gas supply increase.

The United States Natural Gas Fund (NYSEArca: UNG) was down 0.2% Thursday. UNG is up 3.2% year-to-date.

NYMEX natural gas futures were down 0.5% Thursday, trading around $3.69 per million metric British thermal units.

The U.S. Energy Information Administration revealed that the supply rose 46 billion cubic feet for the week ended Sept. 13, compared to expectations of a 55 bcf to 59 bcf increase, reports Myra P. Saefong for MarketWatch.

Natural gas inventories were at 3,299 trillion cubic feet, down 187 bcf year-over-year, but they were 18bcf above the five-year average.

Prices declined as weather forecasts indicated a normal to below-average temperatures across the Midwest and East – natural gas usage in utilities scales back as temperatures fall and consumers cut back on air conditioning.

“I can’t get too excited with regard to the weather forecast from a cooling demand standpoint and it’s too early for significant heating demand,” Stephen Schork, president of Schork Group Inc., said in a Bloomberg article.

Looking ahead, the National Hurricane Center calculates an 80% chance that a tropical cyclone will develop over the Gulf of Mexico in the next five days, Investing reports. Tropical storms disrupt offshore gas rig oeprations.

United States Natural Gas Fund

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Max Chen contributed to this article.