For nearly a year, conditions in the Pacific seemed favorable for the formation of an El Niño – part of a multi-year cycle that creates warmer than average ocean temperatures, and greatly impacts weather and climate around the planet. Analysis by the NOAA Climate Prediction Center confirms that after five consecutive overlapping 3-month periods (e.g., Sept-Oct-Nov, Oct-Nov-Dec, etc.) of average sea surface temperatures in the middle equatorial Pacific being 0.5 oC warmer than their historical average the El Niño has officially taken hold. This image shows the average sea surface temperature for February 2015 as measured by NOAA satellites. The large area of red (warmer than average) can be seen extending through the equatorial Pacific.
The graph below illustrates the warming effect that El Nino years exert on global temps.
I made a video in the spring describing what an El Nino is, and what it’s development might mean for us.
Atmospheric Scientist Kevin Trenberth and Oceanographer Josh Willis speculated about an El Nino developing in the fall of 2014, so the timing is a little bit later than thought, but the main message is this – El Ninos make for a warmer year – and this may elevate the likelihood that 2015 will be yet another record warm year.
In the U.S., the El Niño status is determined by consensus of a team of NOAA scientists who look at the current conditions in the ocean and atmosphere of the tropical Pacific Ocean. They also take into account what computer models predict is likely to happen over the next few months. Although borderline El Niño conditions have persisted since October, with intermittent El Niño conditions last summer, this is the first month that the scientists decided to officially call the El Niño event.
The reason for the change, according to Tony Barnston, chief forecaster at the International Research Institute for Climate and Society (IRI) and member of the ENSO forecast team, is that, “Finally the atmosphere has shown signs of participating in the event; it’s just enough to put it over the borderline of calling it a weak El Niño.” ENSO is a coupled system between the ocean and atmosphere, meaning that they have to engage with each other for the El Niño conditions to strengthen and/or sustain. Sea surface temperatures have been just over the threshold for what’s considered El Niño for several months now, but the atmospheric variables weren’t in place. Now, most notably, tradewinds have become weaker than normal in the central and western equatorial Pacific, said Barnston. The slackening of these tradewinds can lead to more warming of the tropical Pacific Ocean, and the ENSO cycle reinforces itself.
Michelle L‘Heureux, a meteorologist at NOAA’s Climate Prediction Center (CPC) and lead of the ENSO forecast team, offers this explanation for why the advisory was not previously issued, “Snow is snow. ENSO is winds, rain, pressure, surface and subsurface ocean, etc. over a huge expanse of the global tropics (on various timescales). For this reason, it’s tough to pin down whether El Niño is occurring in borderline, weak cases like these. Strong cases are easier because all of the indexes tend to be on the same page.”
The Australian Bureau of Meteorology is showing less confidence that an El Niño event has arrived. They also upgraded their El Niño status this week—from “neutral” to “watch”—but it’s still two levels down in their alert system from an official El Niño declaration.
Now if it could just deliver some rain to California, there’d be some silver lining to offset the generally bad news globally. Average El Nino’s don’t have much record of delivering heavier rain, but the last decent rain year, 2010 for California, did correspond to a reasonable El Nino. This year, except for 2 weeks in December, have been another bust.
The NOAA news release had this to say:
“Due to the weak strength of the El Niño, widespread or significant global weather pattern impacts are not anticipated. However, certain impacts often associated with El Niño may appear this spring in parts of the Northern Hemisphere, such as wetter-than-normal conditions along the U.S. Gulf Coast.”
So it may continue to be a bust for California unfortunately.
Unfortunately, from what I read about this one, it’s not likely to provide any (or much) drought relief. But we’ll see.
Reblogged this on jpratt27.