Adds latest prices

By Scott DiSavino

Sept 3 (Reuters) -U.S. natural gas futures climbed about 4% to a two-week high on Tuesday after the long U.S. Labor Day holiday weekend on a decline in output and increase in gas flows to liquefied natural gas export terminals.

That price increase came despite bearish forecasts for less hot weather than previously expected, which should reduce the amount of gas power generators burn to keep air conditioners humming.

Another factor that has weighed on gas prices for much of this year was the tremendous oversupply of fuel left in storage after a mild winter.

There was still about 12% more gas in storage than normal for this time of year, even though injections have been smaller than usual in 15 of the past 16 weeks after extremely low prices in the spring prompted several producers to cut output. EIA/GAS NGAS/POLL

Front-month gas futures NGc1 for October delivery on the New York Mercantile Exchange rose 7.6 cents, or 3.6%, to settle at $2.203 per million British thermal units (mmBtu), their highest close since Aug. 19.

SUPPLY AND DEMAND

Financial firm LSEG said gas output in the Lower 48 U.S. states slid to an average of 102.3 billion cubic feet per day (bcfd) so far in September, down from 103.2 bcfd in August.

Meteorologists forecast weather across the country would remain mostly near normal through Sept. 11 before turning warmer than normal from Sept 12-18. Energy traders, however, noted that warmer-than-normal weather in mid-September would only average around 75 degrees F (23.9 degrees Celsius), down from an average of 79 F (26.1 C) in mid-August.

LSEG forecast average gas demand in the Lower 48, including exports, will fall from 102.8 bcfd this week to 101.1 bcfd next week. The forecast for next week was lower than LSEG's outlook on Friday.

Gas flows to the seven big U.S. LNG export plants rose to an average of 13.1 bcfd so far in September, up from 12.9 bcfd in August. That compares with a monthly record high of 14.7 bcfd in December 2023.

In Mexico, New Fortress Energy's NFE.O Fast LNG export plant in Altamira received authorization from the U.S. Department of Energy to export LNG to non-free trade agreement countries. That should allow the plant, which turns U.S. gas into LNG, to increase exports.

Looking ahead, Berkshire Hathaway Energy's 0.8-bcfd Cove Point LNG export plant in Maryland will likely shut for about three weeks of routine annual maintenance around Sept. 20, according to the plant's history and notices to customers.

The U.S. became the world's biggest LNG supplier in 2023, ahead of recent leaders Australia and Qatar, as much higher global prices feed demand for more exports due in part to supply disruptions and sanctions linked to Russia's invasion of Ukraine.

Gas prices were trading around $12 per mmBtu at the Dutch Title Transfer Facility (TTF) benchmark in Europe TRNLTTFMc1 and $14 at the Japan Korea Marker (JKM) benchmark in Asia JKMc1. NG/EU

Reporting by Scott DiSavino; editing by Jonathan Oatis

For gas data on the LSEG terminal type ENERGY in the search bar and then go to the GAS drop down and the NORTH AMERICA drop down.

For Interactive Map, type 'Interactive Map' in the box at upper left of the LSEG terminal

For graphics on Baker Hughes rig counts, see: http://graphics.thomsonreuters.com/15/rigcount/index.html

For next-day SNL U.S. gas prices, see: 0#SNL-NG

For next-day SNL U.S. power prices, see: 0#SNL-PWR

For U.S. natgas price and storage polls, see: NGAS/POLL

For U.S. nuclear power outages, see: NUKE/

For U.S. Northwest hydro power report, see: NWRFC

For U.S./Canada natural gas rig count vs Henry Hub futures price, see: http://tmsnrt.rs/2eT9k44

For the U.S. natural gas speed guide, see: USGAS

For the U.S. power speed guide, see: USPOWER

To determine CFTC managed money net position add (NYMEX Henry Hub options and futures combined 3023651MNET) plus (ICE Henry Hub options and futures combined 3023391MNET divided by four) plus (NYMEX Henry Hub swaps options and futures combined 303565BMNET divided by four) plus (NYMEX Henry Hub penultimate gas swaps 303565CMNET divided by four)

NYMEX Henry Hub options and futures combined 0#3CFTC023651

NYMEX Henry Hub futures only 0#1CFTC023651

ICE Henry Hub options and futures combined 0#3CFTC023391

NYMEX Henry Hub swaps options and futures combined 0#3CFTC03565B

NYMEX Henry Hub Penultimate gas swaps 0#3CFTC03565C