Friday, September 5, 2014

Divergent Forecasts Continue

Like a child coming of age in Divergent, as a forecaster one choice can transform you and today that choice is do I join the GFS faction?

The GFS continues to be a dauntless like outlier amongst the various models with regards to the evolution of Hurricane Norbert.  It continues to hold on to a solution in which the remnants of Norbert make landfall near San Diego on Monday.

Source: Wundermap
This contrasts with the gold-standard ECMWF solution

Source: Wundermap
and even the, gasp, NAM.

Source: Wundermap
I'd show the Canadian, but it's pretty much a repeat of the ECMWF and NAM with Norbert tracking more slowly to the northwest and well off the SoCal coast on Monday.

The pros at the National Hurricane Center are clearly leaning toward the non-GFS solution and keep Norbert well south of San Diego through Monday.

Like Beatrice Prior in Divergent chosing Dauntless, perhaps Mother Nature will "chose" the GFS faction.  More likely she will stick with the safe choice and go with the ECMWF–NAM faction. Why the GFS is such an outlier is an interesting problem worthy of investigation, whether it gets it right or wrong.

BTW, if you are interested in reading about rare hurricane impacts on southern California, see The San Diego Hurricane of 2 October 1958 by Michael Chenoweth and Christopher Lansea.


  1. From a modeling perspective, it is fascinating to see how different the GFS solution is. Finding reasons why would be a very cool modeling study.

  2. The difference could be related to cumulus parameterization differences in the two models. That was the primary determining factor in the differences between the GFS and ECMWF for Sandy forecasts with almost no sensitivity to resolution or initial conditions: