|
Save
25% on our special introductory offer.
Subscribe today for only $14.99 per year.
|
|
|
 |
|
Seasonal Forecast
ACTIVE TREND
This year could be the most active season
on record.
Even
before Hurricane Katrina turned to take aim at New Orleans; even before
it gathered strength over the Gulf of Mexico; even before it swept across
southern Florida; even, in fact, before it formed, U.S. hurricane experts
were upping their earlier forecasts and calling for more storms during the
2005 season. The National Oceanic and Atmospheric Administration (NOAA)
in early August warned that the bulk of this season’s storms are still
ahead of us.
NOAA now expects an additional 11 to 14 tropical storms from August through
November, with seven to nine becoming hurricanes, including three to five
major hurricanes. In total, this season is likely to yield 18 to 21 tropical
storms, with nine to 11 becoming hurricanes, including five to seven major
hurricanes, it reports. Earlier, NOAA had predicted three to five major
hurricanes this year (see HP, Summer 2005, page 22).
“This may well be one of the most active Atlantic hurricane seasons
on record, and will be the ninth above-normal Atlantic hurricane season
in the last eleven years,” said Brig. Gen. David L. Johnson, USAF (Ret.),
director of the NOAA National Weather Service.
“Although we have already seen a record-setting seven tropical storms
during June and July, much of the season’s activity is still to come,”
said Gerry Bell, lead meteorologist on NOAA’s Atlantic Hurricane Seasonal
Outlook.
In Fort Collins, CO, William Gray, Philip Klotzbach and the Colorado State
University (CSU) forecast team concur. In August, the team significantly
upped its earlier predictions and issued monthly forecasts for August, September
and October saying they expect all three of these months to be well above
average.
“Based on research data obtained through July, we foresee one of the
most active hurricane seasons on record,” Gray said. “This is
the highest level of hurricane activity we have ever forecast since beginning
seasonal hurricane forecasts at Colorado State in 1984.”
ABOVE AVERAGE LANDFALL RISK, TOO
The CSU team calls for a total of 20 named storms to form in the Atlantic
basin this year. Of these, 10 are predicted to become hurricanes and six
are anticipated to evolve into intense hurricanes with sustained winds of
111 mph or greater.
Gray and Klotzbach issued tropical cyclone forecasts for the specific months
of August, September and October. These newer monthly forecasts are now
in their fourth year. For September, the team predicts five named storms,
four hurricanes and two intense hurricanes. For October, they predict three
named storms, two hurricanes and one intense hurricane. Both of these forecasts
are well above the climatological average.
Another significant focus of the Colorado State team’s research involves
efforts to develop forecasts of the probability of hurricane landfall along
the U.S. coastline. The Colorado State forecast team continues to warn of
the considerably higher than average probability of at least one intense
(or major) hurricane making landfall in the United States this year.
According to their updated forecast, there is a 77 percent chance of an
intense hurricane hitting somewhere along the U.S. coastline during the
remainder of the 2005 season (long-term average is 52 percent). For the
U.S. East Coast, including the Florida Peninsula, the probability of an
intense hurricane making landfall is 58 percent (long-term average is 31
percent). For the Gulf Coast from the Florida Panhandle westward to Brownsville,
TX, the probability is 44 percent (long-term average is 30 percent). The
team also calls for above-average major hurricane landfall risk in the Caribbean
and in the Bahamas.
Conditions that steer hurricanes toward land are well known, but are difficult
to predict on seasonal time scales and are often related to daily weather
patterns. “Knowing precisely where a hurricane will strike and at what
intensity cannot be determined even a few days in advance,” said Max
Mayfield, director of the NOAA National Hurricane Center. Mayfield adds,
“Residents and government agencies of coastal and near-coastal regions
should embrace hurricane preparedness efforts and should be ready well before
a tropical storm or hurricane watch is posted.”
OPTIMAL CONDITIONS
The current confluence of optimal ocean and atmosphere conditions, which
include warmer-than-normal sea-surface temperatures and low wind shear,
has been known to produce increased tropical storm activity in multi-decadal
(approximately 20 to 30 year) cycles. Because of this, NOAA expects a continuation
of above-normal seasons for another decade or perhaps longer.
Similar conditions also produced very active Atlantic hurricane seasons
during the 1950s and 1960s. In contrast, the opposite phase of this signal
during 1970 to 1994 resulted in only three above-normal Atlantic hurricane
seasons in the entire 25-year period. These multi-decadal signals have also
produced a marked decrease in hurricanes in the eastern Pacific hurricane
region.
The last 10 years have witnessed 137 named storms, 77 hurricanes and 38
major hurricanes in the Atlantic basin, according to the CSU team. During
that period—including 2004 when three major hurricanes made landfall—only
six of the 38 major Atlantic basin hurricanes crossed the U.S. coastline.
Based on historical averages, about one in three Atlantic basin major hurricanes
comes ashore in the United States.
The storm seasons spanning 1995 to 2004 comprised the most active 10 consecutive
hurricane years on record, and the Colorado State team believes that 2005
will follow this active trend. The forecasters believe that the United States
is in a new, multi-decadal era for increased storm activity.
“Our research indicates that the United States has entered an era of
increased major hurricane activity which has been reflected in high activity
during eight of the last 10 years,” Klotzbach said. “We expect
this active tropical cyclone era to continue this year and to likely span
the next two or three decades.”
The most active U.S. hurricane season was in 1933 with 21 storms, followed
by 1995 with 19 storms. The most hurricanes in a season was 12 in 1969,
and the highest number of major hurricanes was eight in 1950. |
|
 |
|
|
