The problem with understanding seasonal forecast skill is that statistics and verification numbers don't tell the whole story. In any given year, statistics tells us that on average, we can expect 12-14 named storms. That's why there are just 21 names on the Atlantic name list each year; we're not likely to need more. So if you were to randomly forecast anywhere from 10 to 15 named storms, for example, you'd be very close to correct in almost every season, giving your forecasts the appearance of skill. But in fact, you're just forecasting the obvious -- most seasons are close to these average numbers. To use a statistical term, the standard deviation in the number of storms is usually quite low.
The challenge of forecasting hurricanes is that certain seasons over-perform. By a lot. Like 2004 and 2005. With potentially huge consequences on loss of life and property damage. These outlier seasons are what we're really interested in identifying in advance.
There's a reason why Colorado State University's seasonal hurricane forecast lost most of its financial sponsors many years ago. Their forecasts were well-intentioned and display a small amount of skill, but they are not really useful in identifying outlier seasons --- seasons which are seriously above or below average. Even the NHC forecasts are poor at identifying outlier seasons in advance.
So ask yourself, what evidence do you have that human beings can correctly identify hyperactive seasons in advance? You won't find any. So my point is, seasonal forecasting is in its infancy and does not yet provide meaningful data as to what we're likely to see for 2017. It could be a repeat of 2005. We have no way of forecasting it, aside from some very general trends we might notice in ENSO state. Aside from ENSO and any serious abnormalities in ocean water temperature, we really don't know what we're in for.
Looking at 2017, the conditions look decent. No major ENSO. No wild deviations in Atlantic SSTs. So it's a mystery what we'll get in 2017.
As proof of my assertions, I offer you the NHC Seasonal Forecast for 2005, issued in May. It forecasts only 12-15 named storms. The result was 28 named storms.
http://www.cpc.ncep.noaa.gov/products/o ... icane.html
SUMMARY
NOAA�s 2005 Atlantic hurricane season outlook indicates a 70% chance of an above-normal hurricane season, a 20% chance of a near-normal season, and only a 10% chance of a below-normal season. This outlook is produced by scientists at the National Oceanic and Atmospheric Administration's (NOAA) Climate Prediction Center (CPC), Hurricane Research Division (HRD), and National Hurricane Center (NHC). See NOAA�s definitions of above-, near-, and below-normal seasons.
The outlook calls for 12-15 tropical storms, with 7-9 becoming hurricanes, and 3-5 of these becoming major hurricanes. The likely range of ACE index is 120%-190% of the median. This prediction reflects a very likely continuation of above-normal activity that began in 1995.