NOAA Issues El Niño Watch

NOAA has issued an El Niño Watch for the summer and fall of 2014, giving a 50% chance that an El Niño event will occur. The March 6 El Niño discussion from NOAA's Climate Prediction Center noted that "While all models predict warming in the tropical Pacific, there is considerable uncertainty as to whether El Niño will develop during the summer or fall. If westerly winds continue to emerge in the western equatorial Pacific, the development of El Niño would become more likely. However, the lower forecast skill during the spring and overall propensity for cooler conditions over the last decade still justify significant probabilities for ENSO-neutral. The consensus forecast is for ENSO-neutral to continue through the Northern Hemisphere spring 2014, with about a 50% chance of El Niño developing during the summer or fall."

None of the El Niño models predict La Niña conditions for peak hurricane season, August-September-October 2014, and 8 of 18 predict El Niño conditions. Temperatures in the equatorial Eastern Pacific need to be 0.5°C above average or warmer for three consecutive months for an El Niño episode to be declared; sea surface temperatures were -0.6°C from average as of March 3, and have been +0.1 to -0.7°C from average since April 1, 2013. El Niño conditions tend to make quieter than average Atlantic hurricane seasons, due to an increase in upper-level winds that create strong wind shear over the Tropical Atlantic.


Figure 1. Depth-longitude section of the departure of ocean temperature from average over the equatorial Pacific upper ocean between 0 - 300 meters between 5°S and 5°N during the period February 25 - March 1, 2014. Averages are taken from a 1981 - 2010 base period. While surface temperatures in the Eastern Pacific were near average to cooler than average, a strong eastwards-propagating Kelvin wave with temperatures up to 6°C (11°F) above average at a depth of about 160 meters was headed towards the Eastern Pacific. If unusually strong westerly winds continue over the equatorial Western Pacific during March and April, this Kelvin wave has the potential to trigger a strong El Ninño event over the Eastern Pacific later this year. Image credit: NOAA/CPC.

An impressive westerly wind burst over the Equatorial Pacific
The potential El Niño event has been made more likely over the past month due to the intensification of a strong "Westerly Wind Burst" (WWB) along the equatorial Pacific west of the Date Line. As of March 6, 2014, westerly winds that were more than 10 m/s (22 mph) stronger than average had developed between 140 - 150°E, just north of New Guinea. These unusually strong westerly winds were acting to push warm water piled up to the east of the Philippines eastwards towards South America. The "Westerly Wind Burst" was due, in part, to the counter-clockwise circulation of wind around Typhoon Faxai, which became a tropical storm on February 28 near 9°N, 149°E, and later intensified into a Category 1 typhoon. The Madden Julian Oscillation (MJO), a pattern of increased thunderstorm activity near the Equator that moves around the globe in 30 - 60 days, was also likely involved in amplifying the WWB. In order to keep the momentum of this WWB going and trigger a full-fledged El Niño event, some additional west-to-east push of winds is likely needed during March and April. Some extra push may come from a tropical disturbance (96P) that has developed this week south of the Equator near 13°S 153°E, to the northeast of Australia. The clockwise circulation of air around this storm is bringing increased westerly winds to the Equator in the region of the WWB, and the Joint Typhoon Warning Center is giving this disturbance a "medium" chance of developing into a tropical depression or tropical storm by Friday. The GFS and European models predict that this storm will move southwards and bring heavy rain to the Queensland province of Australia over the weekend.


Figure 2. Departure of the 5-day average west-to-east blowing wind (the "zonal" wind) from average, averaged along the Equator, between 2°S and 2°N. A strong "Westerly Wind Burst" (WWB) formed in January 2014 near 140°E, and has intensified and propagated eastwards along the Equator. As of March 6, 2014, westerly winds that were more than 10 m/s (22 mph) stronger than average had developed. Image credit: NOAA/PMEL.

Additional links
An El Niño Coming in 2014? Guest blog post by Dr. Michael Ventrice on February 21, 2014.
All eyes on the tropical Pacific: March 5, 2014 blog post by Georgia Tech climate scientist Kim Cobb.

Jeff Masters