Year-to-date, 2014 is the 5th-warmest January-April in GISS's records, after 2010, 2007, 2002, and 1998. Only 0.12°C separates 2014 from 2010.
The sea-surface temperatures in the central Pacific ocean are rising -- the weekly Nino3.4 anomaly is now up to 0.5°C -- and models put the probability of an El Nino at 65% or better. This model shows slightly higher projected sea-surface temperatures.
Here's a comparison of this anomaly for 1997-98 and 2014 (left-hand axis), plotted along with the GISS surface temperatures (right-hand axis):
This year is starting out much warmer than 1997 -- 0.26°C warmer, on average.
For the 1997 El Nino, surface temperatures peaked in February 1998, at +0.86°C. Add 0.26°C to that, and you easily get a new monthly record (which is +0.92°C in January 2007).
2010 -- the warmest year so far -- actually cooled after its April -- the yearly average ended up at +0.65°C.
If this coming El Nino comes anywhere close to 1997's, it's likely the 1997-98 temperatures are surpassed, and quite possible the 2010 temperature record is broken.
PS: Michelle L’Heureux wrote on RealClimate:
Could El Niño predictions fizzle? Yes, there is roughly a 2 in 10 chance at this point that this could happen. It happened in 2012 when an El Nino Watch was issued, chances became as high as 75% and El Niño never formed.