NOAA’s seasonal hurricane forecast performed well this year. In May, the Climate Prediction Center predicted a relatively quiet season, with eight to 13 named storms, three to six hurricanes, and one to two major hurricanes. In reality, there were eight named storms, six of which became hurricanes, and two of those became major hurricanes — at least a category 3 on the Saffir-Simpson scale.
Strong vertical wind shear and substantial amounts of mid-level dry air combined to limit tropical cyclone formation across the tropical Atlantic, and as such, only one storm became a hurricane in the tropics, south of 23.5° North.
Although there were not many named storms, it’s worth noting that all of the first three storms became hurricanes, which is something that has not happened since 1992. This year’s “C” storm (Cristobal) was the latest formation of the third named storm since 1992 (Charlie).
Topping out at 125 knots (145 mph), Gonzalo became the strongest hurricane in the Atlantic since Igor in 2010. It was the only storm of the season to become a hurricane in the tropics. Gonzalo also maintained hurricane intensity up to 50.7º North, the furthest north of any storm since Debby in 1982.
Accumulated cyclone energy (ACE) is a metric commonly used for gauging seasonal activity. The 2014 season ended up at 62.5 percent of an average season. As you can see in the chart below, the bulk of a season’s ACE typically comes in August and September, but this year, 46 percent of the ACE was realized in October.
“More ACE was accrued during October (30 units) than during August and September combined (29 units),” said Phil Klotzbach, a research scientist who studies hurricanes at Colorado State University. “The last time that this happened was 1963.”
Major hurricane landfall drought continues for U.S.
2014 is now the ninth year without a major hurricane landfall in the U.S. The last one was Wilma on Oct. 24, 2005, and the unprecedented streak will continue into at least 2015. The only storm to make U.S. landfall in 2014 was Arthur, a category 2 hurricane that bruised the Outer Banks of North Carolina on the night of July 3. It was the strongest U.S. landfall since Ike hit Texas on September 13, 2008.
Another way to look at this statistics is that none of the last 25 major hurricanes in the Atlantic have made landfall in the U.S. According to Klotzbach, an average of 29 percent of all major hurricanes hit the U.S., so the odds of avoiding 25 consecutive storms is about 1-in-5,200.
Florida, one of the climatological hotspots for hurricane landfalls, has not been hit by a hurricane of any intensity since Wilma in 2005. Going back to 1851, the previous longest hurricane-free streak in Florida was 1980-1984 (five years), so the current streak of nine years and counting is utterly unprecedented.
The good luck unfortunately did not apply everywhere in the basin. Bermuda was hit by Fay on October 12 as it was nearing hurricane intensity. Then, just five days later, it got clobbered by Category 3 Hurricane Gonzalo.
It is important to point out that hurricanes do not have any concept of being “overdue” at a particular location. Unlike earthquakes, there is no built-up stress associated with a long period of hurricane-free conditions somewhere. For example, just because a hurricane has not hit Florida in nine years does make it more likely to occur next year. Though extremely unlikely, it could be another nine years until the next one. And as Bermuda found out this year, there’s nothing to say that a specific location can’t get two hurricanes in a week either!
Hurricane forecasts continue to improve
In terms of forecast accuracy, the forecasters at the National Hurricane Center performed better on intensity than their five-year average error at every lead time, and on track at every lead time except for five days.
In the charts below, NHC’s forecaster error for intensity and track is shown by the black line (OFCL), and their average error over the past five seasons is marked by dark red X’s. Two leading global models, GFS (AVNI) and ECMWF (EMXI), and two leading regional models, HWRF (HWFI) and GFDL (GHMI), are also shown on each chart.
For intensity, GFS always outperformed ECMWF, although neither have a high enough spatial resolution to be skilled at forecasting hurricane intensity. The HWRF and GFDL performed well, and were very close to each other at all lead times. NHC forecasters performed extremely well at all lead times.
For track, the HWRF was the clear winner, which is an incredible achievement — it even beat NHC forecasters by some healthy margins. Global models are generally considered the best for track forecasting, so to have a regional model do so well is noteworthy. GFS outperformed ECMWF at every lead time, and GFDL brought up the rear (with the exception of 5 days where ECMWF had the greatest error).
Major upgrades are in store for both GFS and HWRF by the time the 2015 season arrives, so hopefully we will see forecast errors decrease again.
The 2015 hurricane season is now six months away, and the first three names on the list are Ana, Bill, and Claudette. Ana and Claudette are still original names from the 1979 list (it will be their seventh use), and Bill has been in the list since 1997 (it will be its fourth use).
East Pacific season ends as most active since 1992
Hurricane season in the East Pacific also came to a close on Sunday, ending with an amazing 20 named storms. NOAA writes about the busy Pacific season in a press release:
Meanwhile, the eastern North Pacific hurricane season met or exceeded expectations with 20 named storms – the busiest since 1992. Of those, 14 became hurricanes and eight were major hurricanes. NOAA’s seasonal hurricane outlook called for 14 to 20 named storms, including seven to 11 hurricanes, of which three to six were expected to become major hurricanes. Two hurricanes (Odile and Simon) brought much-needed moisture to the parts of the southwestern U.S., with very heavy rain from Simon causing flooding in some areas.“Conditions that favored an above-normal eastern Pacific hurricane season included weak vertical wind shear, exceptionally moist and unstable air, and a strong ridge of high pressure in the upper atmosphere that helped to keep storms in a conducive environment for extended periods,” added [Gerry Bell, lead hurricane forecaster at NOAA’s Climate Prediction Center].