El Nino’s Moody Sister, La Nina in the Works?

May 13, 2016

Forecasters becoming more confident in predicting current fading El Nino will morph into a La Nina later in the year.  Both conditions have a characteristic fingerprint.

Above, NASA JPL’s Josh Willis, interviewed in late 2011, discusses the last time we had an El Nino followed by a strong La Nina. Strong effects on global precipitation, and potentially, the coming hurricane season.

Bloomberg:

A La Nina, a weather pattern marked by a cooling of the Pacific Ocean’s surface, might begin as soon as summer in the Northern Hemisphere, threatening an increase in the number of hurricanes that develop in the Atlantic.

La Nina is the inverse of the warming that characterizes an El Nino pattern. One of the strongest El Ninos on record is now weakening in the equatorial Pacific.

“We are still technically in an El Nino but we are seeing a lot of cold water bubbling up near the coast of South America,” said Michelle L’Heureux, a forecaster with the U.S. Climate Prediction Center in College Park, Maryland. “It is not widespread at this point, but it is indicative to a transition and a fairly quick one.”

Both phenomena can alter global weather patterns. More hurricanes tend to develop in the Atlantic in a La Nina year because it cuts down on wind shear across the basin that can rip budding storms apart. Strong La Ninas also threaten to bring drier conditions across agricultural areas of southern Brazil and flooding to parts of Australia.

The center isn’t making forecasts on the strength of the La Nina yet, in part because many predictive models aren’t always as accurate during spring in the Northern Hemisphere. U.S. forecasters believe there is a 75 percent chance a La Nina will form by the end of 2016, and they are favoring it to develop over the summer, L’Heureux said.

Here, recently released prediction for the coming year from Penn State’s Earth Systems group. You can compare to previous performance.

Previous Forecasts:

Year (click to see forecast)
Prediction
Best Guess
Range
Actual Count
2007 n/a 15 n/a 15
2009 11.5 +/- 3.4 12 8-15 (6-13 if El Niño) 9
2010 23.4 +/- 4.8 23 19-28 19
2011 16.25 +/- 4.0 16 12-20 19
2012 11.2 +/- 3.3 11 8-15 19
2013 16.0 +/- 4.0 16 12-20 14
2014 9.3 +/- 3.0 9 6-12 8
2015 6.9 +/- 2.6 7 4-10 11

Penn State Earth Systems Science Center:

ESSC scientist Michael E. Mann, alumnus Michael Kozar, and researcher Sonya K. Miller have released their seasonal prediction for the 2016 North Atlantic hurricane season, which officially starts on June 1st and runs through November 30th.

The prediction is for 18.9 +/- 4.4 total named tropical cyclones, which corresponds to a range between 14 and 24 storms with a best estimate of 19 named storms. This prediction was made using the statistical model of Kozar et al. (2012, see PDF here). This statistical model builds upon the past work of Sabbatelli and Mann (2007, see PDF here) by considering a larger number of climate predictors and including corrections for the historical undercount of events (see footnotes).

The assumptions behind this forecast are (a) the persistence of current North Atlantic Main Development Region (MDR) sea surface temperature (SST) anomalies (0.88 °C in late-April 2016 from NOAA’s Coral Reef Watch) throughout the 2016 hurricane season, (b) development of a La Niña (Niño3 anomaly of -1°C) in the equatorial Pacific during boreal Fall/Winter 2016-17 (Climate Prediction Center April 2016 ENSO Discussion), and (c) climatological mean conditions for the North Atlantic Oscillation in Fall/Winter 2016-17.

If no La Niña develops (Niño3 anomaly between +/- 0.5 °C), then the prediction will be lower: 16.1 +/- 4.0 storms (range of 12-20 storms with a best guess of 16).

Using an alternative model that uses “relative” MDR SST (MDR SST with the average tropical mean SST subtracted) in place of MDR SST yields a slightly lower prediction (11.4 +/- 3.4 total named storms). This alternative model also includes the development of a La Niña.

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