MIAMI The La Nina weather phenomenon in the
eastern Pacific will likely extend the Atlantic hurricane
season this year, with four more storms forming and two
becoming hurricanes, a noted forecasting team said on Tuesday.
The Colorado State University hurricane research team
boosted its season forecast from 15 to 17 storms, of which six
would be hurricanes. Thirteen storms have already formed this
year and four of those have become hurricane.
The CSU team, founded by forecasting pioneer Bill Gray and
now led by researcher Phil Klotzbach, also said it expected
Tropical Storm Karen to be raised to hurricane status in a
post-season analysis, increasing the hurricane total to seven.
The official six-month Atlantic hurricane season runs from
June 1 to November 30, but historically the busiest part ends
The CSU forecasters said typically the end of the season is
marked by rising wind shear, a difference in wind speeds at
different altitudes that can tear apart hurricanes. But the
formation of the cool-water La Nina phenomenon in the eastern
Pacific could change that pattern this year.
"We expect La Nina conditions through this fall. La Nina
conditions tend to reduce levels of vertical wind shear in the
tropical Atlantic and therefore, the end of the Atlantic basin
hurricane (season) will likely be extended this year," the
While the season so far has seen more tropical storms than
normal, surprisingly strong wind shear has prevented many from
strengthening and made them short-lived.
A month ago, the Colorado State team predicted the season
would produce 15 tropical storms, of which seven would become
hurricanes and four would be major hurricanes with winds over
110 mph (177 kph).
Its preseason prediction, issued at the end of May, was for
17 tropical storms with nine hurricanes and five major
The latest forecast called for one more "major" hurricane,
Category 3 or higher on the five-stage Saffir-Simpson scale of
hurricane intensity with sustained winds topping 110 mph (177
The season has already seen two major hurricanes, Dean and
Felix, both of which reached Category 5, the top rank on the
five-stage Saffir-Simpson scale of hurricane intensity.
Dean skirted Jamaica and then hammered Mexico in August and
Felix struck Central America in early September, killing scores
of people. It was the first time two Category 5 hurricanes have
hit land in the Atlantic basin in a single season since
record-keeping began in 1851.
The long-term average for Atlantic hurricane seasons is
about 10 storms, of which six become hurricanes. There were 28
named storms in 2005, a record-setting year, and 15
strengthened into hurricanes, including Katrina, which killed
1,500 on the U.S. Gulf Coast and swamped New Orleans.