09 April 2015

CSU issues hurricane forecast: 'Quiet' season expected

For the 32nd consecutive year, Colorado State University issued a long-range seasonal outlook for hurricane activity in the Atlantic.  Seasonal prediction of hurricane activity is done by several groups and agencies now, but the pioneer was Bill Gray in the early 1980s.  Several of his students through the years made great contributions to the techniques, and since the early 2000s, Phil Klotzbach has been an integral part of the forecasts.  Since 2006, Phil has been the lead author, and in 2016, Bill Gray will be stepping down from the forecasts (not sure why... he'll only be 86).  During my 13+ years at CSU, I often chatted with Bill, Phil, and others about the forecasts, conditions, etc and gained an appreciation for the process and the curiosity that inspires it.

When you see/hear/read about these seasonal outlooks, it is important to understand what they mean to you.  An active season does not mean you will get hit by a hurricane or two, and an inactive season does not mean that no storms will affect you.  "Active" and "inactive" are relative to the average... so even during inactive years there will still be hurricanes, just fewer than average.  But if there are only 4 hurricanes, and 3 of them make landfall near you..... well, you get the point.

What purpose do they serve??  I outlined a few reasons for making them in the last section of this blog post from September 2013 (scroll down to "Why bother forecasting seasonal activity at all?").

CSU's April forecast for the 2015 season, by the numbers:

  • Tropical Storms --- 7 (58% of average)
  • Hurricanes --- 3 (46% of average)
  • Major Hurricanes --- 1 (50% of average)
  • Overall Activity (ACE) --- 40 (43% of average)

The primary reasons for the below-average forecast:

  • the current weak El Nino is expected to amplify to a moderate or strong El Nino
  • ocean temperatures across the key regions of the Atlantic are cooler than average

They also search through the historical data for "analog" years, or years when large-scale conditions most closely match what we're seeing so far this year.  Those seasons are 1957, 1987, 1991, 1993, and 2014. Out of a total of 20 hurricanes that occurred during those years, the only U.S. landfalling ones were Audrey (1957), Floyd (1987), Bob (1991), and Arthur (2014).

You can read the entire report HERE which includes many more important details than I highlighted in this brief post.

Atlantic hurricane season officially begins on June 1, but storms can and have formed before that, and sometimes the first storm forms well after that date.