A wind shear environment unfavorable to hurricane development across the tropical Atlantic, which is being driven by a recently developed El Nino event in the tropical Pacific, has prompted Andover, MA-based WSI Corp. to further reduce the number of hurricanes it expects to form during the 2009 Atlantic hurricane season. WSI also said cooler-than-normal temperatures will remain in place over much of the eastern United States for the next three months, while above-average temperatures will continue to dominate the West.

WSI's tropical forecast now calls for a total of 10 named storms, including five hurricanes, with two of them intense (Category Three or greater) forming by Nov. 30. The National Weather Service's National Hurricane Center has reported no tropical cyclones in the Atlantic basin this year.

In its initial hurricane forecast for the 2009 season WSI had predicted 13 named storms, three of them intense (see NGI, Jan. 5). But a continuation of relatively cool tropical Atlantic Ocean temperatures, combined with unusually cold temperatures in the eastern equatorial Pacific and normal to above-normal wind shear in the tropical Atlantic, prompted the forecaster in April to reduce those numbers to 11 named storms, including six hurricanes, with two of them intense (see NGI, April 27). Last month WSI said it was sticking to that forecast (see NGI, June 29).

The impacts of the El Nino event -- the warming of surface temperatures in the central and eastern equatorial Pacific Ocean, which can influence the formation of Atlantic hurricanes -- have emerged more quickly than originally expected, resulting in reduced expectations for the upcoming season, WSI said.

"Ocean temperatures in the tropical Atlantic remain quite cool relative to the temperatures during the last 15, more tropically active years," said WSI seasonal forecaster Todd Crawford. "Further, the new El Nino event continues to strengthen, resulting in an unfavorable wind shear environment across the tropical Atlantic. The early development of this enhanced wind shear along with the relatively cool tropical Atlantic temperatures will almost certainly result in a less active season than last year, and could potentially result in an unusually quiet season. We have reduced our forecast numbers slightly to account for the impacts of the new El Nino event, and the fact there have been no early season storms through mid-July."

The number of tropical storms forecast by WSI would be fewer than occurred during the 2008 season, when a total of 16 named storms, including eight hurricanes, five of them intense, formed in the Atlantic. But it would be about the same as an average hurricane season, which has 11 named storms, including two major hurricanes, according to the National Oceanic and Atmospheric Administration (NOAA).

NOAA has said eastern equatorial Pacific sea surface temperatures were at least one degree Centigrade above average at the end of June, signaling the arrival of a new El Nino event (see NGI, July 13). El Nino events, which occur every two to five years and typically last about 12 months, can help suppress Atlantic hurricane activity.

The consensus forecast has been for a relatively mild hurricane season. Colorado State University (see NGI, June 8), NOAA (see NGI, May 25) and AccuWeather.com Chief Long Range Forecaster Joe Bastardi (see NGI, May 18) have all predicted fewer hurricanes this year.

In an Energycast Outlook issued last Wednesday, WSI said areas from the Southwest to the Pacific Northwest may be especially warm through October compared to historic temperature norms.

In its forecast for August WSI predicted cooler-than-normal temperatures across the East and North-Central regions, with warmer-than-normal temperatures expected to be in place across the rest of the country.

Power-sector demand for natural gas, sparked by warmer temperatures in the Southwest and dry conditions in the Northwest, will be largely offset by the continuing cool weather in the East, according to Paul Fleming, Energy Security Analysis Inc. director of power and gas.

"Barring any significant hurricane activity, power-sector demand for natural gas in August will not reverse the trend of well-above-average [storage] inventory build rates and will result in continued pressure on prices," Fleming said in a statement issued in conjunction with WSI's outlook. "For the power markets in the East, the big news is that there will be a reduced likelihood of heat events in August, even after a very mild July."

In September WSI expects warmer-than-normal temperatures to move into the Northeast and North-Central regions, with cooler-than-normal temperatures to remain in the Southeast. Warmer-than-normal temperatures are expected to continue to dominate the South-Central and West regions, with much-warmer-than-normal temperatures expected in Texas and the Southwest.

"Due to prevailing warmer temperatures in the West, natural gas demand from the power sector should be above average in September, but this higher demand will not likely offset the trend towards very high inventories in early November," and higher price volatility can be expected in Texas and the Southwest, Flemming said.

By October cooler-than-normal temperatures will have returned to all of the East except Florida, while the West and South-Central regions will continue to experience warmer-than-normal temperatures, according to the WSI forecast. For a second consecutive month, much-warmer-than-normal temperatures will bake Texas and the Southwest, WSI said.

Flemming said shoulder season dynamics should overshadow weather variations in October. Power prices during the month will be supported by generator maintenance, and gas demand from the power sector should be supported by coal plant maintenance and nuclear refueling, Fleming said.

The WSI seasonal outlooks reference a standard 30-year norm (1971-2000). The next forecast, for September-November, is scheduled to be issued Aug. 26.

Cooler-than-normal weather in the Northeast this summer could be a hint that a cold, snowy winter is in store for an area stretching from Boston to Washington, DC, according to Bastardi (see NGI, July 20). Like WSI, Bastardi said he expects a period of more typical summer heat in the Northeast to be followed by a return of cooler weather to the region. Bastardi also said late-summer heat and humidity will prevail across the Southeast for much of the rest of the summer, and the hot weather that has gripped Texas, Oklahoma, Arkansas and Louisiana will remain, though the heat should be less extreme.

Taking into account its own forecast of mild summer weather, Barclays Capital recently said it expects just a 0.1 Bcf/d uptick in natural gas demand for power generation during May-September compared with the same period last year.

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