The official start of the 2015 Atlantic hurricane season begins on Monday (6/1), and a lot is being made about what to expect for the summer. With that, we checked in with our resident meteorological expert Jacob Meisel to get his expert take on what to expect this season, and we have provided a summary of his comments below. Jacob heads up our Bespoke Weather Service research package which includes weekly analysis of the weather’s impact on the natural gas market, daily notes, and trading alerts. If you are interested in this service, please ping Jacob using our contact form.
The general consensus among most forecasters is that the current season is forecast to be below-average, and it’s a forecast we agree with. Like any seasonal or long range forecast, though, predicting the strength and intensity of a hurricane season is an imperfect science. However, there are some key indicators that we as meteorologists are able to use to determine what are some of the most likely scenarios. One of the main indicators we look to is the variation of sea surface temperatures across the central Pacific Ocean from their historical average, more commonly referred to as the La Nina/El Nino cycle. These temperature trends have global impacts on weather patterns, and thus are crucial to any forecast.
Over the past few months, we have established a weak El Nino, with a February/March/April (FMA) El Nino Southern Oscillation (ENSO) value of 0.5. This indicates sea surface temperatures were around half a degree above average through that timeframe. Looking at how sea surface temperatures impact the hurricane season before it begins, we ran historic FMA ENSO data against historic Accumulated Cyclone Energy (ACE) data for the Atlantic Ocean. The ACE may sound complicated, but put simply it is a measure of the activity of each hurricane season. Higher readings are indicative of a busy and strong season while low readings indicate hurricane seasons with less activity. As the chart below illustrates, any correlation between the two series was extremely inconclusive.
As the FMA ENSO value is the most recent data point we have available, we had to rely on our computer model projections for El Nino strength to determine our expectations for the hurricane season. A wide range of climate models around the world showed a consensus of a very strong El Nino, with the July/August/September (JAS) ENSO value predicted to be generally between 0.7 and 1.7 (a very wide range, but predicting El Nino strength is also an imperfect science).
One of the primary pieces of guidance, the CFSv2 climate model, though likely overdone, is predicting an even stronger El Nino when going into hurricane season.
What does the data show about JAS ENSO and the Atlantic ACE index? While the correlation is not very strong, it certainly exists.
Perhaps the biggest story here is that whenever the JAS ENSO value is over 0.6 (the odds of which are 80-90% this year), the highest ACE value has been 137. The National Hurricane Center defines any season with an ACE at or above 111 as an abnormally active season, and a “hyperactive” season has been defined elsewhere as a season with an ACE value above 153. As mentioned earlier, the JAS ENSO forecast range for El Nino is between 0.7 and 1.7 this season. No historical El Nino within this range has yielded a hyperactive season since officials began tracking these statistics in 1950, and only two of the eight years featured abnormally active seasons. Meanwhile, four of the eight years yielded hurricane seasons that were abnormally inactive (Atlantic ACE 66 or lower).
Though a small sample size, this trend shows one of the key reasons that numerous weather services are forecasting a below-average hurricane season. As always, there still remains the possibility of an active season, but it looks to be only at around 20-25%, with the chance of an inactive season much more likely. In terms of real economic impacts, however, all this analysis is irrelevant anyways. It only takes one major storm to make landfall in the United States to cause devastation and change the public interpretation of the hurricane season, and this is something that cannot be forecast more than a week or two in advance. Even the slowest seasons can still produce one or two very strong storms. Thus, once the seasonal drivers are identified and analyzed, forecasting economic impacts from the tropics really just becomes a waiting game.