Severe drought conditions on Long Island have expanded from central Suffolk to include almost all of the county, as well as southeast Nassau, according to Thursday’s update of the U.S. Drought Monitor.

“Severe” is the third of the monitor’s five categories, with the fifth, exceptional drought, being the most intense. The only part of Suffolk not under the severe drought designation is a sliver of the northwest part of the county in the Town of Huntington.

Precipitation since March, as of day-end Wednesday, is 10.71 inches below normal at Long Island MacArthur Airport, the Island’s official weather monitoring site, the third driest period since records started being kept in 1984, said climatologist Jessica Spaccio of the Northeast Regional Climate Center, based at Cornell University.

What’s more, the outlook is not promising for drought relief over the coming months.

The long-range forecasts for both October and the period from October through December indicate tilts in favor of above-normal temperatures, with insufficient data to make calls for precipitation, said Matthew Rosencrans, head of forecast operations with the Climate Prediction Center, on a Thursday media call.

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“Above-normal temperatures can increase evaporation, exacerbating the dry conditions,” Spaccio said, with not just normal, but above-normal precipitation needed to make a dent in the drought.

Indeed, “the long lead outlooks do not hold good news for the Long Island drought,” she said.

In July the state Department of Environmental Conservation said New York was under a drought watch — raising that on Aug. 3 to warning level for the western part of the state, where some areas are now in extreme drought.

According to the DEC’s website, “There are no statewide mandatory water use restrictions in place under a drought watch or warning but residents are strongly encouraged to voluntarily conserve water.”

Also in July the Suffolk County Water Authority posted a request on its website, urging consumers to “conserve water whenever possible.”