There has been little doubt for several months, but now it is certain: 2015 will be the hottest year on record by far.
Data from NASA, with my guesswork from July 2015 shown in dashed and dotted lines.
November would have set another monthly record, except that October was revised upwards by two-hundredths of a degree. As it is, this is the hottest November on record. For 2015 not to be a record year, December would have to come in with a below-zero anomaly and that is not happening.
Note to readers: my guesswork is not an expert forecast, but a what-if exercise I did a few months ago in an attempt to predict average anomalies for 2015 and 2016. I will not be updating my guesses as reality proves them wrong. But I would welcome improved forecasts from readers who understand the El Niño and surface temperature dynamics better than I do.
The annual anomaly chart below shows the projection (which assumes that December is as warm as November) by the red x, 0.862 °C above the 1951-1980 baseline. My guess from July 2015 for 2015 is shown as the red square and for 2016 by the orange dot.
It is now certain that we have set two record years in a row, something that last happened in 1980-1981. It is even possible, given a persistent El Niño, that 2016 will be hotter than 2015, which would give three record years in a row, something that has not happened since at least 1880.
Update
Here’s Sou’s year-to-date graph:
And a longer perspective, from Things Break:
Finally, a plot by Gavin Schmidt and his estimation that 2015 has a greater than 99.999% chance of being the hottest calendar year.
Gavin’s Tweet is followed by interesting discussion about what the pre-industrial baseline should be. This is actually a practical discussion, since all the world’s countries just committed to targets relative to “pre-industrial” without a clear definition of what the baseline is. A shift of 0.1 or 0.2° C could make all the difference in whether attaining the new 1.5° C aspirational target is impossible or merely extremely difficult. Expect to hear more about this.
Critical Angle 
2015 is certain to pass all other years in terms of the temperature anomaly value. In terms of the likelihood that it will exceed all other years on record given the statistical errors for each year my calculations show 98% probability for GISTEMP and 99% for NOAA. My April qualitative ‘forecast’ was that 2015 would surpass 2014 by a wide margin. My late August estimate was 0.10°C above 2014; this will turn out to err 0.02 to 0.04°C on the low side.
A remarkable year. I guess the (non)hiatus is over.