Prognostic Meteorological Discussion
Issued by NWS
FXUS24 KWNC 051711
EL NINO/SOUTHERN OSCILLATION (ENSO) DIAGNOSTIC DISCUSSION
CLIMATE PREDICTION CENTER/NCEP/NWS
and the International Research Institute for Climate and Society
5 March 2015
ENSO Alert System Status: El Nino Advisory
Synopsis: There is an approximately 50-60% chance that El Nino conditions will
continue through Northern Hemisphere summer 2015.
During February 2015, El Nino conditions were observed as the
above-average sea surface temperatures (SST) across the western and central
equatorial Pacific became weakly coupled to the tropical atmosphere. The latest
weekly Nino indices were +0.6C in the Nino-3.4 region and +1.2C in the Nino-4
region, and near zero in the Nino-3 and Nino-1+2 regions. Subsurface
temperature anomalies increased associated with a downwelling oceanic Kelvin
wave, which was reflected in positive subsurface anomalies across most of the
Pacific. Consistent with weak coupling, the frequency and strength of low-level
westerly wind anomalies increased over the equatorial Pacific during the last
month and a half. At upper-levels, anomalous easterly winds persisted across
the east-central Pacific. Also, the equatorial Southern Oscillation Index
(EQSOI) remained negative for two consecutive months. Convection was enhanced
over the western equatorial Pacific and near average around the Date Line.
Overall, these features are consistent with borderline, weak El Nino
Compared to last month, several more models indicate El Nino (3-month
values of the Nino-3.4 index equal to or greater than 0.5C) will continue
throughout 2015. This is supported by the recent increase in subsurface
temperatures and near-term model predictions of the continuation of low-level
westerly wind anomalies across parts of the equatorial Pacific. However, model
forecast skill tends to be lower during the Northern Hemisphere spring, which
contributes to progressively lower probabilities of El Nino through the year.
In summary, there is an approximately 50-60% chance that El Nino conditions
will continue through Northern Hemisphere summer 2015.
Due to the expected weak strength, widespread or significant global
impacts are not anticipated. However, certain impacts often associated with El
Nino may appear in some locations during the Northern Hemisphere spring 2015.