For the first time since the fall of 2012, weekly-averaged sea surface
temperatures (SSTs) in the equatorial Pacific have reached the threshold
needed for an El Niño event to be declared. By definition, an El Niño
episode occurs when SSTs are at least +0.5°C from average for three
consecutive months in the region 120°W - 170°W, 5°S - 5°N (called the
Niño 3.4 region.) The weekly
ENSO update
issued by NOAA on May 12, 2014, put ocean temperatures in this Niño 3.4
region for the past seven days at +0.5°C from average. An El Niño event
is still not a sure thing, though. We saw similar behavior in the fall
of 2012, with SSTs warming up above the +0.5°C threshold, prompting NOAA
to issue an El Niño Watch. However, the ocean SSTs were not able to
hold for the required three month period, and no El Niño event ended up
happening. However, this year the odds appear more favorable. NOAA has
issued an El Niño Watch for the summer and fall of 2014, giving a
greater than 65% chance that an El Niño event will occur during summer, a
boost upwards from their >50% chance given the previous month. The
May 8
El Niño discussion from NOAA's Climate Prediction Center noted that
"There
remains uncertainty as to exactly when El Niño will develop and an even
greater uncertainty as to how strong it may become. This uncertainty is
related to the inherently lower forecast skill of the models for
forecasts made in the spring." None of the
El Niño models
(updated in mid-April 2014) predict La Niña conditions for peak
hurricane season, August-September-October 2014, and 16 of 20 predict El
Niño conditions. There is currently not a strong
Westerly Wind Burst
(WWB) over the equatorial Pacific Ocean helping push warm water
eastwards towards South America. There have been three of these WWBs so
far in 2014, and if we get one more in the next month or two, that
should be enough to push the system into a full-fledged El Niño event.
Figure 1. Departure of sea surface temperature (SST) from average
for May 12, 2014. A plume of warmer-than-average temperatures stretched
along the equatorial Pacific from the coast of South America westwards
into the Western Pacific, a harbinger of a developing El Niño event.
Image credit:
NOAA.El Niño events usually lead to quiet Atlantic hurricane seasons 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. The last official El Niño event
occurred from summer 2009 - spring 2010, and as expected, the
2009 Atlantic hurricane season
was a relatively quiet one, with 11 named storms, 3 hurricanes, and 2
major hurricanes. No 2009 hurricanes got their names retired, and there
were only six fatalities.
NOAA Launches ENSO Blog Just in time for the likely arrival of El Niño comes the new NOAA
ENSO Blog
(ENSO is the acronym for “El Niño - Southern Oscillation”, which is the
more scientifically rigorous term for what I typically refer to as “El
Niño.") The blog is written by a team of three veteran El Niño
scientists:
• Anthony (Tony) Barnston, chief forecaster at the International Research Institute (IRI) for Climate and Society
• Emily Becker, a researcher at the NOAA’s Climate Prediction Center (CPC)
• Michelle L’Heureux, who has led the team in charge of routinely producing NOAA/NWS/CPC’s
ENSO updates and outlooks since 2006
They
have not yet enabled comments, but they expect to do so within the next
week or two. I look forward to seeing their expert commentary.
Jeff Masters - Wunderground
