User blog:YE/2015 Pacific hurricane season April outlook

Happy April! April Showers bring May flowers, but here in the Nevada desert, there is no rain at this time of year. Flowers are blooming and the days are getting longer and longer! Winter has been record warmth this year here in Vegas, but will that carry over to the hurricane seaosn?

Intro
In 2013, an unusually powerful +NPO block was noted across the Gulf of Alaska. This spark, which not only triggered a very cold winter across the US that year, warmed the water since high pressure means warmer sea surface temperature. This is at least partially responsible for a +PDO flip that was noted in early 2014, and sparked the EPAC in 2014.

2014 recap
As you guys probably know and remember very well, the 2014 Pacific hurricane season was a banner and magical year for the basin. It started off strong with Hurricanes Amanda and Cristina and never looked back. Exceeding all expectations, activity was non-stop until November, and ended up with 22 named storms, a record-tying 16 hurricanes, and 9 major hurricanes (5 knots short of a record-tying 10, stupid Vance could never clear out an eye).

El Nino
Signs of an El Nino can be traced back to late 2013, when record sea surface temperatures developed off the coast of the Philippines due to the lack of el Nino events over the previous several years. Then, in November, the greatest tropical cyclone of all time, Typhoon Haiyan, struck the Philippines. This sparked a westerly wind burst, and the warm pool migrated westward. Despite some setbacks, an El Nino developed by fall 2014, also aided by an unusually warm sub-surface pool that rivaled the one prior to the 1997 super El Nino event. It peaked in December, before weakening in early 2015. However, this El Nino has been fairly stable since then, and has even deepened slightly.

Will we get a super El Nino?
As of March 2015, a new warm subsurface pool has developed below the surface along the equatorial Central Pacific, arguably stronger than the one noted prior to the 2014 season. Cyclone Pam, the greatest tropical cyclone to ever exist in March, sparked a massive westerly wind burst. The reason why a westerly wind burst is so important is because during the aforementioned westerly wind burst, the trade wind pattern is reversed from it's traditional easterlies, to westerlies. These winds transport the very warm waters near Asia west, and since the sea surface temperatures are warmer in the West Pacific than the Central Pacific (hence why more TC's form in the WPAC than the CPAC), the WPAC-born waters, when located in the CPAC, are warmer than normal.

Around the same time as Pam formed, an unusually powerful MJO pulse migrated across the Pacific. Since record keeping of the MJO began in 1974, the March 2015 MJO episode along the Pacific was the highest on record, surpassing. This also helps spawn WWB's, and has already had major effects. Nino region 1+2 has warmed dramatically, from -1.5C to 1.2C in a a matter of weeks. Furthermore, this could help reduced shear in the EPAC in a long run.

Regarding the future, models all agree on the El Nino continuing through 2015, although many models have a warm bias when it comes to ENSO. The March 2015 model plume average was +1.2C, a moderate El Nino. Currently daily estimates have the strength of this El Nino at +0.75C. Given the warm-subsurface pool and the decrease of ocean temperatures across the WPAC, which prevented a super El Nino last year, it would not surprise me if we got a strong or even super El Nino, though the latter is a bit far fetched.

PDO
Now, onto the Eastern Pacific forecast. We appear to be re-entering the active era. PDO first became positive in early 2014 for the first time in years. Since then, the PDO signal has onyl gotten stronger, and by June, it was near-record levels. After weakening slightly that fall, the PDO came back with a vengeance in early 2015, and has been at record levels for the past few months, with totals near +2.50. This is a strong indication that the +PDO era has returned, which was dominant from 1976-1998. During that time span, the Eastern Pacific was at its most active levels ever seen in history, and until 2014, included the 5 most active EPAC seasons in history. Until 2014, the post-1998 time frame was consisted of -PDO mostly, although around 2005, a secondary blip of +PDO was noted. As such, from the late 1990s until 2013, the EPAC seasons were largely inactive. Therefore, given that it is unlikely that the +PDO time frame is a blip, I'd say there is a good chance the active era has returned. Given the fact that records prior to 1988 in the EPAC are sketchy due to the EPHC's low bias, as well as the fact that PDO now is stronger than it was for the most part of the 1976-1998 era, this could mean the the EPAC could be even more active than it was during it's 1980's heyday. The PDO is one of the main reasons for the bullish forecast issued below.

Sea surface temperatures
You thought 2014 was warm? Well, 2015 is looking better. 2014 had the second warmest ocean temperatures in EPAC history (satellite era), only trialling 2009, and the three month JAS of 2014 exceeded that of 2009. Pre-sat era, only 1959 was warmer than 2014. 2015 is off to an even better start, however. The months of January, February, and March of 2015 are the warmest on record, satellite era or not.

Here is the chart of the data:

1948  24.659   24.544   25.082   25.912   26.298   26.299   26.574   26.920   26.518   25.763   25.462   25.286 1949   24.769   24.963   24.920   25.577   26.162   26.090   26.512   26.767   26.383   26.062   25.477   24.975 1950   24.580   24.483   25.075   25.548   25.812   25.787   26.201   26.527   26.505   26.108   25.453   24.979 1951   24.694   24.692   24.958   25.407   25.800   26.054   26.589   26.960   26.810   26.753   26.199   25.567 1952   25.115   25.084   25.405   25.863   26.357   26.356   26.537   26.848   26.715   26.447   25.987   25.325 1953   24.935   25.032   25.347   25.971   26.291   26.426   26.811   27.052   26.839   26.416   26.014   25.238 1954   24.964   24.826   25.210   25.723   26.127   26.119   26.371   26.610   26.538   26.262   25.594   25.086 1955   24.696   24.615   25.012   25.416   25.903   26.026   26.280   26.384   26.272   25.552   25.065   24.632 1956   24.328   24.596   24.925   25.391   25.722   25.783   25.946   26.450   26.332   26.061   25.555   25.193 1957   25.003   25.167   25.477   26.071   26.629   26.874   27.309   27.601   27.437   27.052   26.732   26.174 1958   25.766   25.749   26.041   26.493   26.819   27.045   27.249   27.373   27.305   27.004   26.502   25.910 1959   25.709   25.749   25.899   26.386   26.832   26.833   27.136   27.309   27.229   26.822   26.070   25.383 1960   24.879   24.689   25.290   25.984   26.236   26.355   26.810   26.988   26.783   26.402   25.781   25.311 1961   24.889   24.893   25.241   25.747   26.208   26.329   26.538   26.644   26.413   26.243   25.693   25.034 1962   24.626   24.811   25.113   25.493   25.903   25.985   26.453   26.792   26.607   26.268   25.713   25.126 1963   24.849   24.975   25.501   26.272   26.513   26.665   26.900   27.185   27.210   27.095   26.531   25.783 1964   25.191   25.127   25.226   25.692   26.053   26.091   26.415   26.392   26.202   25.952   25.454   24.678 1965   24.390   24.491   25.005   25.741   26.156   26.092   26.409   26.850   26.933   26.801   26.630   25.934 1966   25.312   25.149   25.587   26.176   26.499   26.575   26.882   26.937   26.767   26.444   25.943   25.283 1967   24.874   24.805   25.349   25.815   26.408   26.436   26.648   26.912   26.779   26.456   25.994   25.279 1968   24.807   24.755   25.114   25.801   26.276   26.500   26.743   26.954   26.877   26.668   26.260   25.734 1969   25.523   25.531   25.558   26.162   26.580   26.696   26.869   26.985   26.974   26.700   26.116   25.553 1970   25.147   25.071   25.429   25.999   26.053   26.083   26.076   26.246   26.164   26.025   25.495   24.818 1971   24.284   24.086   24.484   25.029   25.448   25.492   25.874   26.091   26.039   25.730   25.028   24.445 1972   24.297   24.401   24.950   25.740   26.223   26.302   26.776   27.126   27.058   26.966   26.524   26.018 1973   25.391   25.251   25.514   25.709   25.982   25.989   26.281   26.353   26.174   25.918   25.529   24.676 1974   24.440   24.408   24.851   25.437   25.730   25.830   26.151   26.408   26.261   25.984   25.402   24.821 1975   24.316   24.394   24.718   25.248   25.499   25.481   25.746   26.022   25.850   25.561   25.064   24.335 1976   23.837   24.214   24.922   25.308   25.669   26.033   26.422   26.689   26.783   26.798   26.321   25.657 1977   25.195   25.095   25.312   25.605   26.174   26.256   26.684   26.963   26.975   26.628   25.957   25.577 1978   25.385   25.243   25.627   26.172   26.507   26.466   26.618   26.805   26.645   26.532   26.092   25.477 1979   25.145   25.009   25.417   25.997   26.273   26.497   26.640   26.917   26.878   26.885   26.341   25.930 1980   25.715   25.637   26.000   26.125   26.552   26.512   26.650   26.733   26.703   26.295   25.884   25.236 1981   24.784   24.812   25.202   25.722   26.109   26.304   26.459   26.689   26.841   26.679   26.261   25.909 1982   25.348   25.294   25.724   26.549   26.862   26.776   26.768   27.176   27.278   26.892   26.574   26.036 1983   25.624   25.415   25.560   25.913   26.455   26.658   26.889   26.911   26.713   26.592   26.307   25.788 1984   25.149   25.184   25.552   25.765   26.167   26.200   26.408   26.583   26.585   26.314   25.784   25.092 1985   24.594   24.543   25.064   25.601   26.135   26.293   26.541   26.790   26.851   26.678   26.209   25.513 1986   25.100   25.241   25.471   26.179   26.573   26.461   26.805   27.147   27.201   26.789   26.531   25.969 1987   25.240   25.374   25.482   25.800   26.490   26.610   26.859   27.053   27.544   27.175   26.759   26.106 1988   25.507   25.311   25.665   26.200   26.658   26.198   26.394   26.404   26.460   26.190   25.873   24.988 1989   24.397   24.220   24.648   25.684   26.239   26.401   26.712   26.753   26.590   26.311   26.296   25.467 1990   24.966   25.037   25.602   26.451   26.847   26.849   26.987   27.247   27.145   26.948   26.406   25.802 1991   25.542   25.387   25.855   26.283   26.669   26.698   27.014   27.106   27.160   26.716   26.210   25.528 1992   25.012   24.979   25.561   26.130   26.904   27.085   26.933   27.142   27.079   26.853   26.544   25.808 1993   25.572   25.691   25.943   26.424   26.893   26.921   26.916   27.052   26.827   26.904   26.645   26.243 1994   25.866   25.764   26.135   26.610   26.780   26.805   27.147   27.138   27.264   26.996   26.612   25.765 1995   25.498   25.592   26.005   26.236   26.524   26.623   26.827   26.867   26.835   26.546   26.238   25.715 1996   24.755   24.927   25.339   25.824   26.310   26.492   26.637   26.974   26.976   26.699   26.140   25.329 1997   24.908   24.830   25.245   25.837   26.587   27.091   27.302   27.784   27.820   27.458   27.069   26.339 1998   25.726   25.491   25.652   25.882   26.608   26.691   26.837   27.181   26.974   26.545   25.968   25.156 1999   24.558   24.551   24.875   25.489   25.888   26.022   26.188   26.391   26.272   25.800   25.494   24.751 2000   24.310   24.511   24.884   25.573   26.097   26.150   26.457   26.777   26.713   26.452   25.931   25.351 2001   24.932   24.777   24.971   25.494   26.037   26.218   26.633   27.139   27.028   26.651   26.320   25.582 2002   24.923   24.733   25.281   25.992   26.381   26.339   26.722   27.040   26.972   26.893   26.294   25.857 2003   25.304   25.531   25.776   26.065   26.542   26.543   26.718   27.193   27.293   26.903   26.573   25.675 2004   25.228   25.073   25.507   26.034   26.456   26.638   26.791   27.207   27.137   27.071   26.466   25.640 2005   25.405   25.341   25.577   26.052   26.516   26.652   26.672   26.975   27.026   26.472   25.970   25.448 2006   24.968   24.855   25.290   26.062   26.323   26.278   26.780   27.194   27.228   27.143   26.435   25.655 2007   25.038   24.999   25.327   25.908   26.168   26.362   26.690   26.761   26.836   26.364   25.706   25.132 2008   24.345   24.407   24.875   25.414   26.007   26.079   26.303   26.854   26.788   26.538   26.071   25.434 2009   25.015   25.015   25.377   26.030   26.469   26.920   27.193   27.579   27.738   27.551   26.658   26.226 2010   25.513   25.362   25.431   26.052   26.350   26.273   26.364   26.561   26.496   26.076   25.564   24.695 2011   24.287   24.247   24.776   25.496   26.005   25.871   26.070   26.477   26.589   26.199   25.680   24.972 2012   24.622   24.666   24.843   25.594   26.027   26.073   26.444   26.755   27.042   26.886   26.349   25.905 2013   25.048   25.061   25.176   25.965   26.614   26.470   26.818   27.129   27.001   26.831   26.241   25.627 2014   25.053   25.310   25.888   26.335   26.770   27.010   27.402   27.600   27.286   27.314   26.773   26.160 2015   25.756   25.828   26.105

These totals are much warmer than even 1992.

On another note, the SST configuration could put Baja California Sur and Hawaii at high risk for strikes, though a cool pool northwest of the islands, and only slightly above normal (cooler than last year) ocean temperatures exist. However, SST's near Hawaii started to warm up considerably at this time last year, so we'll see. Even if the sST's near Hawaii do not warm up, a pool of above average ocean temperatures east of Hawaii could callow systems to maintain their strength.

Other factors
In addition to the warm ocean temperatures, wind shear has been below average and vertical instability was above average. Vertical instability favors stronger storms, and wind shear also favors more storms and stronger ones in general. Both are positive factors for 2015. However, if Nino 1+2 region cools down a bit, wind shear could be much stronger, and thus, prevent storm formation. Conversely, if things stay were they are, 2015 could rival 1992 in activity.

Negative factors
The QBQ is not as - as it was last year. -QBQ favors more systems but of slightly less quality? Now the odds of a re-2013? Small. First of all, the very high vertical instability should help in that department. Secondly, it is tough to imagine a 1 or 2 major year in a multi-year El Nino event.

Another negative factor could be a possible late start to the season due to El Nino and the warm Nino region 1+2. The reason for this is the factor that cooler rather than warmer waters off the South American coast favors a more northerly ITCZ due to the fact cool waters means drier air, which means higher pressures in that part of the world, which forces the ITCZ upward. Howe3ver, I'd still favor an early start based on recent trends, as over the past 15 years, we have average a little over a storm per May. The reason for this is that the -IOD has been persistent since e1999, and favors a more northern ITCZ. This is also aided by a cool Gulf of Guinea and an Atlantic Nina, which favors higher pressure, which once again lifts the ITCZ up. The position of the ITCZ is very important in determining the start of the EPAC season. When the TICZ lands at around 10N, the EPAC season usually starts. Though sometimes if the ITCZ gets too north as in 2013, that could be bad as well, since the storms are forming close to cool waters. This was an big time issue in 2013.

Overall
Overall, I forecast the following numbers for 2015:


 * 23 named storms
 * 10 hurricanes
 * 5 major hurricanes
 * ACE:152 (Above average, but not hyperactive)

Confidence in this prediction is high, but if wind shear can remain low, it would not surprise me if 2015 was much active than indicated above. Given the above forecast, it is likely that the activity level observed in 2015 will be comparable, if not busier, to the 2014, as well as the glory days of the 80s and 90s.