Isaac, a Category 1 hurricane as of late Tuesday, was expected to make landfall near the mouth of the Mississippi River at about 7 p.m. CDT and then jog slowly through the night toward New Orleans before striking there early Wednesday, the National Hurricane Center (NHC) said.

At 4 p.m. CDT Issac had maximum sustained winds of 80 mph and was "getting better organized" as it approached southeastern Louisiana at about 8 mph, NHC said. Flooding from the storm surge and rainfall were expected ahead of the landfall, and thousands already had reported power outages along the Louisiana coast, according to Entergy Corp.

Hurricane-force winds on Tuesday afternoon extended outward up to about 60 miles, mainly to the northeast and east of the center, according to the NHC. At high tide Isaac's peak storm surge was expected to be six to 12 feet in parts of Mississippi and southeastern Louisiana; four to eight feet in Alabama; three to six feet in south-central Louisiana and the Florida Panhandle; and two to four feet in Apalachee Bay, FL.

Isaac was expected to drench the Gulf Coast with seven to 14 inches of rain, with isolated amounts of up to 20 inches, over most of Louisiana, southern Mississippi, southern Alabama and the "extreme" western part of the Florida Panhandle.

Isaac was upgraded to hurricane status at midday Tuesday after reconnaissance data from Air Force Reserve hurricane hunter aircraft indicated that the storm had achieved maximum winds of 75 mph.

Based on reports submitted by Gulf of Mexico operators at 11:30 a.m. CDT Tuesday, an estimated 66.7% of current daily natural gas production in the Gulf of Mexico (GOM), or just above 3 Bcf/d, had been shut in as of Tuesday midday, said Interior's Bureau of Environmental Enforcement (BSEE). About 93.28% of daily oil output also had been shuttered. The production percentages are calculated using information submitted by offshore operators in daily reports, with shut-in output based on the amount expected to be produced that day.

Personnel had been evacuated from a total of 503 (84.4%) of the 596 manned offshore production platforms, BSEE said. Workers also had been evacuated from 49 (64.47%) of the 76 rigs currently operating in the GOM.

No major onshore or offshore damage is expected to energy infrastructure, said Tudor, Pickering, Holt & Co. (TPH) analysts Tuesday. "The slow forward motion is likely to cause flooding inland but should not create long-term impact to oilfield operations."

Because of the bounty from shale gas, the impact on U.S. midstream operations has been "largely refocused" from the Gulf Coast, said TPH, but eastern GOM pipelines and Louisiana-based natural gas liquids infrastructure "remain exposed. We expect modest impact, but prolonged outages can impact 3Q2012."

Williams' Geismar, LA, petrochemical operations are the "most exposed" as they provide 7% of the company's gross earnings and 13% of Williams' "dividend-ready cash." Kinder Morgan Inc. "has small" exposure, with less than 3% of its gross earnings from Gulf-based terminals, TPH said.

Meanwhile, a new tropical depression has formed in the Atlantic with maximum sustained winds near 35 mph, according to the NHC. The depression, which was about 1,240 miles east-northeast of the Lesser Antilles and moving west-northwest at 10 mph late Tuesday, could become a tropical storm in the next day or so.

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