El Nino Advisory 2015

June 9, 2015

El Nino Advisory 2015

The National Weather Service has currently listed on the ENSO Alert System Status: El Niño Advisory

Synopsis: There is an approximately 90% chance that El Niño will continue through Northern Hemisphere summer 2015, and a greater than 80% chance it will last through 2015.

 Definitions of the ENSO ALERT SYSTEM.
El Niño or La Niña Watch: Issued when conditions are favorable for the development of El Niño or La Niña conditions within the next six months.El Niño or La Niña Advisory: Issued when El Niño or La Niña conditions are observed and expected to continue.Final El Niño or La Niña Advisory: Issued after El Niño or La Niña conditions have ended.

NA: ENSO Alert System is not active.

The reason for this forecast according to NOAA:

Sea surface temperatures in the equatorial Pacific remained substantially above average during April. Also, there is still a lot of warmer-than-average water below the surface in the upper 300 meters of the ocean, helping to ensure that the above-average sea surface temperatures will continue for at least the next few months.

The atmospheric response to the warmer waters in the equatorial Pacific in February strengthened through March and April: the Trade winds are more westerly than average, upper-level winds are weaker than average and more rain was present in the central equatorial Pacific. These are all signs present during El Niño events, and act to reinforce El Niño events.

What does this mean for us?

The tropical Pacific is in the early stages of the pattern that can bring drought to parts of Asia and rains to South America, and ocean temperatures will probably stay above thresholds through the southern hemisphere winter and at least into spring, the Australian Bureau of Meteorology said.

The last El Nino was from 2009 to 2010 and the Pacific has either been in its cooler state called La Nina, or neutral since then. The pattern can crimp the hurricane season in the Atlantic, bring more rain across the southern U.S. and warm some northern states. It heralds a drier winter and spring in Australia’s east. Warm anomalies in the Pacific in March and April were very similar to those observed in 1997, a year of an “intense” El Nino, Meteo-France said last month.

The most substantial US temperature and rain impacts from El Niño occur during winter. Right now, it’s too early to forecast with much confidence the effect this El Niño may have on the US next winter. (Although the good chance that this El Niño will last into winter does tilt the odds towards the expected temperature and precipitation impacts.)

The Australian Bureau of Meteorology has just raised their event tracker to “El Niño” status, the equivalent of issuing an El Niño Advisory for us. (They have slightly different thresholds for declaring the onset of El Niño.) El Niño events are linked to increased drought and heat waves in Australia, especially during their winter (our summer), so they monitor its evolution closely.

Also, since it’s very likely that this event will continue through the summer, we may see some effects on the tropical cyclone seasons. The western Pacific tropical cyclone season is off to a roaring start, with seven named storms so far (the average is two!), which is likely linked to the warm Pacific waters.

Sources: Barnston, A. G., M. H. Glantz, and Y. He, 1999: Predictive skill of statistical and dynamical climate models in SST forecasts during the 1997/98 El Nino episode and the 1998 La Nina onset. Bull. Amer. Meteor. Soc., 80, 217-243.
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