By Scott DiSavino

Oct 16 (Reuters) -U.S. natural gas futures slid about 3% to a three-week low on Wednesday on expectations mild weather over the next two weeks will keep demand low.

Front-month gas futures NGc1 for November delivery on the New York Mercantile Exchange fell 6.7 cents, or 2.7%, to $2.431 per million British thermal units by 8:07 a.m. EDT (1207 GMT), putting the contract on track for its lowest close since Sept. 19.

One factor weighing on prices in recent weeks has been a reduction in the amount of gas power generators have burned after Hurricanes Milton and Helene knocked out electric service to millions of homes and businesses.

There were still about 82,000 customers without power in Florida from Milton, which hit the state on Oct. 9, and 10,000 out in North Carolina from Helene, which hit Florida on Sept. 26 before moving inland.

In total, Milton caused around 3.4 million customers to lose power, while Helene caused roughly 6 million outages.

The U.S. National Hurricane Center, meanwhile, projected there was a 40% chance that a disturbance in the Atlantic Ocean would strengthen into a tropical cyclone over the next week as it moves toward Puerto Rico and the Bahamas.

In the spot market, pipeline constraints caused next-day gas prices at the Waha hub NG-WAH-WTX-SNL in the Permian Shale in West Texas to turn negative for a record 37th time this year.

Until now, Waha prices have remained in positive territory since mid September - just after the Matterhorn pipe from the Permian to the Houston area started receiving gas.

Waha prices first averaged below zero in 2019. It happened 17 times in 2019, six times in 2020 and once in 2023.

SUPPLY AND DEMAND

Financial firm LSEG said average gas output in the Lower 48 U.S. states slid to 101.3 billion cubic feet per day (bcfd) so far in October from 101.8 bcfd in September. That compares with a record 105.5 bcfd in December 2023.

That's because many producers reduced drilling activities earlier this year after average spot monthly prices at the U.S. Henry Hub NG-W-HH-SNL benchmark in Louisiana fell to a 32-year low in March. Prices have remained relatively low since then.

On a daily basis, output was on track to drop by 2.4 bcfd over the past two days to a preliminary five-month low of 99.6 bcfd on Wednesday. Analysts have noted that preliminary data is often revised later in the day.

Energy analysts blamed part of the daily output decline on planned maintenance on Kinder Morgan's El Paso Natural Gas pipe, which transports gas from the San Juan, Permian and Anadarko basins to California.

Meteorologists projected the weather in the Lower 48 states will turn from colder than normal on Oct. 16-17 to mostly warmer than normal from Oct. 18-31.

With warmer weather coming, LSEG forecast average gas demand in the Lower 48, including exports, will slide from 98.1 bcfd this week to 95.5 bcfd next week. The forecast for this week was higher than LSEG's outlook on Tuesday, while its forecast for next week was lower.

The amount of gas flowing to the seven big U.S. LNG export plants rose to an average of 12.8 bcfd so far in October, up from 12.7 bcfd in September. That compares with a monthly record high of 14.7 bcfd in December 2023.

Reporting by Scott DiSavino; Editing by Kirsten Donovan

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