La Nina coming, with SW drought, SE hurricanes
Federal climatologists say that conditions in the tropical Pacific are shifting toward a full-fledged La Nina event this fall. That could mean a deepening drought in the southwestern United States, and ripening conditions for an active autumn hurricane season.
In a release this morning, the National Oceanic and Atmospheric Administration's Climate Prediction Center said surface waters in the eastern and central Pacific are cooling. The green color in the map, along the equator west of South America show the cooler-than-average sea-surface waters.
"While we can't officially call it a La Nina yet, we expect that this pattern will continue to develop during the next three months, meeting the NOAA definition for a La Nina event later this year," said Mike Halpert, acting deputy director for the Climate Prediction Center, in Camp Springs, Md.
La Nina events typically mean wetter-than-average weather in the Pacific Northwest, and drier-than-average weather in the Southwest. "These conditions also reinforce NOAA's August forecast for an above-normal Atlantic hurricane season," said Gerry Bell, NOAA's lead seasonal hurricane forecaster.
La Nina winters in Baltimore are typically poor snow-producers. But there have been exceptions. Since 1950 there have been 9 winters with moderate-to-strong La Ninas. None produced a storm with 8 inches of snow or more. There were 7 winters with weak La Ninas. They produced only two storms of 8 inches or more. But those were sizable. They included the 22-inch storm in January 1996, and a 15-inch snowfall in January 2000. El Nino winters - when the Pacific is unusually warm - tend to be bigger snow-makers in Baltimore.
La Nina events are declared when average sea surface temperatures in the eastern and central equatorial Pacific, measured over three months, move more than 0.9 degrees Fahrenheit below the average. For months, forecasters have been predicting weak La Nina ocean temperatures for this summer. Those conditions now appear to be developing, with some portions of the east-central Pacific now a degree or two below long-term averages.
