The Coast (Likely) is Clear
Little activity is expected for the reaminder of the 2006 season.

by Howard Shingle


When all is said and done, the 2006 hurricane season is most likely to end up average. Through the end of September, the forecast team at Colorado State University (CSU), Fort Collins, CO, reports “average hurricane activity” for the season.

June and July began with “about average” activity, the CSU team notes. August was an inactive month; September had above-average activity; and during the first week of October the team expected to see below-average activity for the month largely due to developing El Niño conditions in the central and eastern Pacific. For November, the CSU team pointed out that hurricane activity that month is very rare in El Niño years.

Most notable for this season is the fact that U.S. landfall has been well below average. No hurricanes have made landfall along the U.S. coastline this year.

OCTOBER-NOVEMBER
Specifically, in its October-only forecast the CSU team calls for two named storms and one hurricane (no major hurricanes). It forecasts no tropical cyclone activity in November.

Tropical cyclone activity in November is not very frequent. Since 1950, only 27 percent of years have witnessed the development of one or more hurricanes, the team reports. Only four years since 1950 have had a major hurricane develop in November. The probability of named storm, hurricane and major hurricane development becomes even less likely in El Niño years.

The trend of no hurricanes making landfall is likely to continue through the end of the season. The CSU forecast team has recently developed a methodology for calculating the probability of hurricane landfall along the entire U.S. coastline. Based on a 1950-2001 data, it has calculated the probability of various intensities of tropical cyclones making landfall over the rest of the season. It places the probability of a Category 1 or 2 hurricane making landfall at 14 percent, and of a Category 3, 4 or 5 hurricane making landfall at four percent—both figures below average.

UNEXPECTED EL NIÑO
The 2006 hurricane season will be considerably less than the seasonal activity the CSU forecast team anticipated in earlier forecasts—first issued in early December 2005 and updated in early April, late May and early August. By the August forecast the team had lowered by two the number of hurricanes it expected this season to seven with three expected to be major (Category 3, 4 or 5).

“We judge this reduced seasonal activity to be due to mid-level dryness in the tropical Atlantic (with large amounts of African dust), which greatly reduced August activity and to the rapid late summer development of an El Niño event, which we and nearly all [El Niño] forecasts did not anticipate,” the CSU team reported October 4.

June and July 2006 had about average activity with two named storms forming during the two-month period (Alberto and Beryl). The June and July long-period (1950-2000) average is approximately 1.5 named storm formations and 0.6 hurricane formations. Unlike 2005 when two major hurricanes (Dennis and Emily) developed and intensified in the tropical Atlantic and Caribbean, there was no activity in the deep tropics during June and July 2006.

August had about average named storm activity, but the amount of hurricane and intense hurricane activity was well below average. Only one hurricane formed during August (Ernesto), and it lasted less than one day due to interaction with Caribbean basin landmasses. Unexpected subsidence, dry air and mid-level dust across the tropical Atlantic during the month of August are believed to be the primary contributors to the surprisingly inactive August. This subsidence is believed to be a result of the development of weak El Niño conditions in the eastern and central equatorial Pacific.

The team’s September forecast was on target. Even though conditions in August were not favorable for Atlantic cyclone activity, it predicted that they would likely become more favorable for hurricane development in September, and this prediction verified quite well. Four named storms (Florence, Gordon, Helene and Isaac) formed during September, and all four of these storms became hurricanes. Gordon and Helene became major hurricanes.