LMV,
I agree, the ECMWF model is usually slightly more accurate, but typically not until the forecasts are beyond 5 days out. GFS is more accurate 1 day out and both GFS (as long as one uses GFS 12Z and 00Z forecasts rather than 6Z or 18Z) and ECMWF models are generally equal up to 4-5 days out. I believe when it comes to longer range forecasts (6-10 days) the ECMWF has more skill. Nonetheless, The GFS model has backed off some regarding TC activity. However, it still suggests that TC and westerly wind (or possibly a WWB) is likely. 12 of the 13 phase diagrams of the MJO index forecast (which come from the U.S., U.K., Japan, Australia, Brazil, Taiwan, and Europe) suggest that an active phase of the MJO ranging anywhere from weak to moderate in strength, will enter the West Pacific in early December, and then reach the Dateline before mid December. Also, the GFS shows a CCKW entering the West Pacific just before the MJO, but close enough together that the combination of the two should increase the odds TC and WWB activity. Therefore, I suspect that we'll see at least some level of westerly wind associated with TC activity in the West Pacific during early to possibly mid December. Will it be a legit WWB? It's certainly possible. The easterly wind/enhanced trades we've had over the past few weeks have pushed warm surface water back into the Western Pacific, and allowed the Central/Eastern equatorial Pacific to cool down some (being in between Kelvin waves doesn’t help either). Westerly wind in the West Pacific and near the Dateline would (among other things) reverse that (or at least improve it), and cause the West Pacific to cool down and the Central/East Pacific to warm back up some. Also, it would likely provide a more favorable environment for the Kelvin wave in the East Pacific to surface. If the West equatorial Pacific were to cool off and the Central equatorial Pacific were to warm back up slightly, mixed with the MJO and CCKW activity, the Walker Cell could transition (due to the effects that the MJO and CCKW activity would have on atmospheric circulation and the equatorial Pacific SST gradient).
I'm partial to GFS driven models for few reasons: (a) I've been using GFS driven models to track Pacific marine weather on a regular basis for about 15 years now (SIDE NOTE: Not to be so repetitive about being a surfer from So Cal, but one of the most important factors in knowing when and where to surf, is being able to know and understand how to track weather. Especially, marine weather.), (b) The surf forecast sites who's weather and wave forecast models I use, are mainly GFS driven, and (c) Using GFS driven models for so many years (as they are by far one of the most abundant weather forecast models available on the web) I've become very familiar with them. All forecast models go through brief periods in which they forecast poorly. Identifying those periods can be done by watching model trends and continuously referencing real time data of what actually happened with what the forecast models were suggesting would happen. (NOTE: In the northern hemisphere, forecast models tend to be more
accurate inaccurate during summer than the winter. So the accuracy of forecast models should improve some in the coming months). IMO, the GFS model is currently forecasting fair-good in the short range (about 1-4 days out), and fair in the long (about 5-8 days out). Like I said though, I heavily rely on real time data as well as forecast data.
I also found the answer as to why the GFS 12Z (and 00Z, but I prefer the 12Z) forecasts are more accurate than the 06Z and 18Z. The following excerpt comes from the linked AccuWeather article on the secrets of weather forecast models, exposed:
http://www.accuweather.com/en/weather-blogs/weathermatrix/why-are-the-models-so-inaccurate/18097Look at model trends. If the low pressure moved east with this run, what did it do the run before that? For the GFS, look at a couple days of 00Z and 12Z runs for consistency. Avoid the 06Z and 18Z runs when 00 or 12 is available; in the U.S. these runs don't include the weather balloon network data (balloons are only sent up twice per day), and are therefore radically different and more likely to have bias.
EDIT: I decided to add the attached plot from NOAA, which shows the historical accuracy/skill of the U.S. GFS, the European ECMWF, the U.K. Government's UKMET, and a CDAS. Northern Hemisphere (top) and Southern Hemisphere (bottom). (NOTE: While other models have been upgraded/tweaked over the years to increase accuracy, CDAS has never been modified, supposedly to serve as a constant). Notice that during the past few years, the difference in accuracy between the GFS and ECMWF for 5-day forecasts of 500-hPa heights, has been relatively minor. Especially, for the N. Hemisphere. According to NOAA, the GFS upgrade is now scheduled for Jan 7, 2015, and should bring it right on par with the ECMWF.
2nd EDIT/ADD ON: I just wanted to point out that while the active/enhanced phase of the MJO would likely support the currently evolving El Nino, the inactive/suppressed phase of the MJO would likely interfere. Of course, this would be due to the easterly wind/anomalies and suppressed convection associated with the inactive phase of the MJO as it moves through the Western and Central Pacific. The easterly wind/anomalies and suppressed convection that we just saw move through the Western and Central Pacific during mid to late November was associated with the inactive/suppressed phase of the MJO. Now we're about to see the active/enhanced phase of the MJO move through the Western and Central Pacific, and if another inactive/suppressed phase of the MJO follows behind that, then it's possible that a more normal northern hemisphere winter time MJO pattern/signal may be returning/strengthening (i.e. alternating active and inactive phases). Not saying that it is, bit if this is the case, then it (especially during the inactive phase) would likely disrupt the evolving El Nino conditions in both the ocean and atmosphere (i.e. SST's and Walker Circulation). This is likely why during El Nino conditions, the MJO signal typically weakens (I believe that's mostly true during moderate-strong El Ninos where the Walker Cell transitions into a solid El Nino configuration by early-mid fall of the first year in which the El Nino develops, but not always as true during weaker El Ninos). The issue with this possible El Nino event, is that it's a late bloomer due to it's extremely slow evolution. Therefore, if the Walker Cell fails to transition, and if the MJO signal returns, it may NOT give the 2014-15 El Nino much of a chance to fully develop the necessary ocean-atmosphere coupling. What the MJO signal and Walker Circulation do over the next few weeks will be important. I believe this is partly why Kyle MacRitchie stated the following back on Nov 24: “
The current state of the low-frequency (ENSO timescale) convection, combined with the impending CCKW and MJO loads the dice in El Niño’s favor. If the MJO doesn’t develop as advertised over the next few weeks then I think the chance of an El Niño drops significantly”.