La Niña is on track to develop later this fall, raising the chances of more weather like Tropical Storm Debby in South Carolina, the latest forecast shows.

The National Weather Service’s Climate Prediction Center issued its updated forecast Thursday morning for La Niña, holding steady with it’s July prediction that the weather pattern would likely form this fall. La Niña typically leads to more severe Atlantic Hurricane seasons and drier winters for the Southeast.

Tropical Storm Debby began life as a Cat 1 hurricane when it first struck Florida on Monday. Debby was soon downgraded to a tropical storm as it moved up toward South Carolina. The slow-moving storm has dumped heavy rain and caused significant flooding in parts of the state all week.

La Niña forecast

According to the latest forecast, there is a 66% chance of La Niña emerging between September and November. There is also a 74% chance that La Niña will persist from November through January.

The Atlantic hurricane season started June 1 and lasts through November.

What is La Niña?

La Niña is the opposite of El Niño. Trade winds are even stronger than usual during La Niña events, pushing warm water toward Asia. Off the west coast of the U.S., upwelling increases, bringing cold, nutrient-rich water to the surface. These cold waters in the Pacific push the jet stream northward.

What does La Niña mean for hurricane season?

La Niña is known to enhance hurricane activity in the Atlantic basin, according to NOAA.

NOAA currently predicts an above-normal hurricane season with between 17 and 25 named storms. Of particular note for South Carolina as Debby moves through is that Atlantic hurricane season is usually most active between mid-August and mid-October — the period when La Niña is currently expected to emerge.

Hurricane activity tends to increase under La Niña due to its effects on wind shear and atmospheric conditions over the Atlantic. There is a reduction in wind shear in the tropics when La Niña occurs, which can encourage hurricane development. Wind shear means a change in wind speed and direction with height in the atmosphere.

La Niña also favors greater hurricane activity by decreasing atmospheric stability and reducing the amount of sinking motion in the atmosphere.

La Niña winter weather impacts

The effects from La Niña tend to trigger drought conditions in the Southeast, according to the National Oceanic and Atmospheric Administration.

“The dryness over the Southeast is often associated with the Pacific-North American (PNA) climate pattern,” NOAA states. “In the pattern’s negative phase, the general flow of the atmosphere gets “stuck” in a wave train that repeatedly brings higher-than-normal pressure to the North Pacific, lower-than-normal pressure to western Canada, and, farther downstream, higher-than-normal pressure to the Southeast. High pressure generally results in dry skies.”

Below is a map that shows the average influence La Niña has had on winter precipitation in the U.S. over the past 60 years.

Meanwhile, despite the rainfall from Debby, many parts of South Carolina are still under some level of drought, according to the U.S. Drought Monitor.

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