Welcome to this outlook; doing something I have not done in quite some time. 2014 and 2015 were some of the most banner, yet tiring years in the Eastern Pacific's long history. Does the season continue on it's 2014 and 2015 legacy, or do we head down a new path?
Due to the activity of the 2013 Pacific typhoon season, which resulted in a series of insane intense typhoons, a westerly wind burst, in which the warmer waters of the West Pacific are moved to the Central and Eastern Pacific, was triggered, which combined with a warm sub-surface Pacific, sparked a weak El Nino event by September 2014. This Nino event stayed weaker than what most expected for much of 2014, but as the normally warm waters of the West Pacific cooled in early 2015, resulting in the atmospheric conditions more resembling an El Nino event, the sub-surface began to warm again, along with a strengthening +PDO and strong support within the CFS and ECMWF models, and speculation of a super El Nino returned. This time the speculation proved correct, and the result was the strongest El Nino in recorded history, with SST's in Nino 3+4 exceeding 2.0C for several months, and briefly exceeded 3.0C. By March, this Nino event began to weaken rapidly at last, and by May, the Nino had died completely.
Since last fall, global models have at least been hinting at a La Nina event this summer. This appears to be verifying. A cool sub-surface pool was seen as early as February, and by May, stronger traditional easterly trade winds, have returned. For whatever reason, the climate models have backed off the forecast of a La Nina somewhat, but I advise you to not fall for it, as models tend to be conservative right before July and January, when either an upwelling (cold water) or downwelling phase of a Kelvin Wave (warm waters) develop, and ENSO forecasts by computer models become much more aggressive. A quick look at the historical dataset suggests that following a super Nino, a weak La Nina around -.8C is likely. However, one must remember we are also in a +PDO era, and that often, if the very weak La Nina from 1983-85 is any proof, SOI, the main basis for ENSO records prior to around 1979, tends to stay somewhat negative during strong +PDO regimes like this one. Henceforth, I think it is reasonable to assume that in reality the Nina will peak around -1.5C.
So let's now take a step back and think what in most people's eyes La Nina means to the EPAC. Most people who read this, and post on places like Strom2k or to a lesser extent WU or AmericanWx, especially if they track these systems more casually, think La Nina is to the EPAC like what Donald Trump is to the Republican party. An indication of a dead season.
Well it's not that simple. A quick look at ENSO and PDO datasets one will point out two things. First, the EPAC tends to be quite favorable during +PDO spikes. Secondly, it seems some post-Nino years tend to do better than others. Well, why is that? There are two reasons. The first reason is quite simple, -PDO makes the background state for the EPAC quite unfavorable especially in a developing, rather then a stagnant La Nina. Secondly, the strngeth of the previous Nino. If an El Nino event is largely sub-surface driven and not driven by a temporary or even decade-long +PDO spike, it is likely that a cool sub-surface pool emerges as Nino fades (like what we are seeing this year), leaving the EPAC devoid of energy, and conditions overall are less conducive, despite the persistent +PDO pattern that sometimes occurs when this happens. This occurred during El Nino events of 1972-73, 1994-95, 1997-98, 2009-10, and appears to be happening against this year. From the list, the notable El Nino of 1982-83 is missing. Why? Since that dinn't leave the EPAC devoid of energy thereafter and only slowly converted to a La Nina that existed mostly in the Central Pacific, evident by historic Nino 1+2 readings and its slow weakening allowed for an El Nino base state to be maintained.
tl;dr 2016 is no 1983, and the El Nino base state from 2014-15 no longer exists.
So far we haven't had anything since Pali aside from 1E. While shear hasn't been too bad, vertical instability is below average and pressures have been higher than normal. The EPAC monsoon trough has returned to the Caribbean while the MJO seems mostly stuck in the Indian Ocean. Assuming this pattern continues, the EPAC is in for a dismal hurricane season.
However, there's some reasons to be excited. +PDO is at record levels and we have had the 2nd warmest EPAC SST's on record from February to May. In addition, climate models (except for the ECMWF) do generally suggest below normal shear and average to above average rainfall across the EPAC in future months, but until we actually get some activity, given the tendency of the GFS and ECMWF to overdue genesis, I am going to remain extremely skeptical. However, if what I mentioned above comes to fruition, the season could be busier than listed below, which is perhaps too biased towards extrapolation of the lack of activity seen so far.
Despite the La Nina, the season may have a bit of an oddball pattern. Normally, when we think of La Nina and EPAC, one thinks of the typical genesis shift from the CPAC to right offshore Mexico. I don't think we see this shift this season. The reason mostly has to do with SST configuration. First of all, this Nina seems EPAC biased, meaning that the difference between the CPAC equatorial SST's and the EPAC equatorial SST's is small, much like a Modoki El Nino, which favors shear further west than normal. Secondly, we have a +PDO horseshoe configuration, with cooler anomalies at high latitudes from 125W to 150W. These two factors favor tropical cyclones further west than normal, but due to northward ITCZ due to cooler 1+2 favoring high pressure there, I expect most storms to form further northwest, rather than southwest than normal.
In terms of land impacts, Hawaii tends to get hits from the east in La Ninas since there is little ridging over that island, not to mention the expected northwesterly track bias this year. Given the trends of the last several years, I also think the Baja California Peninsula is at higher than normal risk for a tropical cyclone impact, but I feel like I say this every year.
- 11 named storms
- 4 hurricanes
- 2 major hurricanes