Summer heat, which has so far been “more impressive and widespread than anticipated,” will continue to blanket most of the country into the autumn, according to forecasters at Andover, MA-based WSI Corp., who also reaffirmed their prediction of an “active-normal” 2011 Atlantic hurricane season.

“The extreme drought across the southern Plains has resulted in record heat in that part of the country. The drought has also acted to anchor the heat across much of the eastern two-thirds of the country, while the West has remained relatively cool, so far. We don’t foresee a significant change in pattern for the remainder of the summer, although the focus of the heat may shift slightly farther to the west in August,” said WSI Chief Meteorologist Todd Crawford.

“As we progress into fall, the pattern will generally be driven by the northern Pacific Ocean signal, which strongly argues for very warm temperatures across much of the eastern two-thirds of the U.S., especially in the north-central and northeastern states. For the August-October period as a whole, we are forecasting 587 population-weighted cooling degree days. This is much higher than the 1971-2000 average of 498, but slightly lower than last year’s extreme value of 603.”

In its previous forecast, WSI said much of the country could expect temperatures to average warmer than normal throughout the summer, with population centers in the Northeast likely to experience increasingly intense and widespread heat into September (see NGI, June 27). WSI’s steamy outlook is significantly different than MDA EarthSat Weather’s forecast of summer temperatures averaging 14.5% cooler than last year (see NGI, May 23), while AccuWeather.com forecasters have said they expect the lingering effects of a recent La Nina event to translate into a “year without a summer” for the nation’s midsection (see NGI, June 6).

According to WSI, warmer-than-normal temperatures will dominate all of the country in August except Florida, coastal California and the Northwest, which will be cooler than normal. But the cooler weather in those areas won’t be enough to offset the bullish underpinnings across the rest of the country, according to Energy Securities Analysis Inc. Senior Analyst Chris Kostas.

“With natural gas inventories running 7.7% below last year’s level (and 2.0% below the five-year average) through mid-July, the forecast for warmer-than-normal temperatures over most of the country in August will make it difficult for inventories to close the gap,” Kostas said in a statement issued in conjunction with WSI’s outlook.

“Increased gas demand from [electricity grid operators] ERCOT, MISO, New York, New England and PJM should keep natural gas prices firm, despite the huge increases in year-over-year gas production.”

With WSI’s temperature forecast map unchanged for September, gas prices are likely to remain relatively firm, Kostas said.

“Implied market heat rates and power prices in ERCOT, MISO, PJM, New York and New England should run high in September, as above-normal power demand combines with the beginning of the generator maintenance period to push prices up the supply curve,” he said. “Power prices in California and Florida are likely to be spared from the higher implied market heat rates seen east of the Mississippi, as cooler-than-normal temperatures combine with seasonal decreases in weather-related demand.”

Warmer-than-normal temperatures will remain in place over most of the country in October, with the Northwest, coastal California and Florida remaining the only exceptions, according to the WSI outlook.

“While cooling demand tapers off significantly in October, the generator maintenance period typically takes a great deal of generation offline. Even a minor increase in weather-related demand could have a meaningful effect on heat rates as a result,” Kostas said. “With warmer-than-normal temperatures expected in ERCOT, MISO, PJM, New York and New England in October, increased power demand and the onset of the generation maintenance period should keep gas demand firm. Implied market heat rates and power prices are also likely to be firm on marginal late-season cooling demand.

“With a much warmer-than-normal August to October period expected for most of the country, we now expect inventory levels to have trouble challenging last year’s record 3,840 Bcf by the end of the injection season. Natural gas prices are also unlikely to collapse significantly in October due to the much warmer-than-normal temperatures that are expected this summer.”

WSI is scheduled to issue its next seasonal outlook on Aug. 23.

Two months into the 2011 Atlantic hurricane season four named storms have formed and none of them have seriously threatened energy interests, but WSI forecasters said they still expect 15 named storms, including eight hurricanes, four of them Category Three or greater — the same as the 1995-2010 average — to form this year.

“Most of the important drivers for tropical activity continue to indicate that an active-normal season lies ahead of us, including warmer-than-normal North Atlantic water temperatures, very low surface pressures in the main development region, and no impending El Nino event,” Crawford said.

The consensus forecast this year is for an above-average hurricane season, with the National Oceanic and Atmospheric Administration, AccuWeather.com and MDA EarthSat all calling for above-average numbers of named storms and hurricanes. Forecasters at Colorado State University have said they expect to see 16 named storms form in the Atlantic Basin by Nov. 30, with nine turning into hurricanes, five of them major hurricanes.

WSI first predicted an active-normal hurricane season in April and reaffirmed that forecast last month. WSI forecasters have also said they expect the 2011 season to have more impact on the U.S. coastline than the last two hurricane seasons, which produced no landfalling hurricanes. The Gulf Coast is under a significant threat for hurricane landfall, according to WSI, which said it expects two or three landfalling hurricanes this year.

“The forecast numbers from our model are quite similar to those prior to the 2008 season, when Hurricanes Dolly, Gustav and Ike impacted Louisiana and Texas,” Crawford said.

A total of 19 named storms formed in 2010, with 12 of them becoming hurricanes, including five intense hurricanes. The long-term (1950-2009) averages for the Atlantic hurricane season are 10 named storms, six hurricanes and two intense hurricanes; the 1995-2009 averages are 14, eight and four, respectively.

The first named storm of the 2011 hurricane season, which officially began June 1, was Tropical Storm Arlene, which formed June 29 and made landfall in northeastern Mexico before dissipating over the Sierra Madre Mountains July 1. Tropical Storm Bret, which formed north of the Bahamas July 17, and Tropical Storm Cindy, which formed in the central Atlantic Ocean three days later, both dissipated in the North Atlantic late last week without ever making landfall.

On Friday the National Hurricane Center (NHC) was tracking Tropical Storm Don, which was located east of Brownsville, TX and was expected to make landfall by early Saturday between the Rio Grande and Matagorda. The storm, which had maximum sustained winds of 50 mph on Friday morning, was expected to weaken after making landfall, according to NHC.

NHC on Friday was also monitoring a large tropical wave accompanied by a well-defined low pressure system located about 1,200 miles east-southeast of the Lesser Antilles. That system had a 30% chance of becoming a tropical cyclone over the weekend, NHC said.

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