Dweymiller@vines.colostate.edu
Friday, June 5, 1998
RAPIDLY FADING EL NINO WILL PUT 1998 HURRICANE SEASON CLOSE TO
AVERAGE, SAYS COLORADO STATE'S HURRICANE EXPERT GRAY
Note to editors: Forecast totals are in the attached chart. A taped
interview with Professor William Gray is available by calling
(970) 491-1525. The complete hurricane forecast, plus related
research and press releases, are available on the World Wide Web at:
http://tropical.atmos.colostate.edu/forecasts/index.html
FORT COLLINS--In a report released today, Colorado State
University hurricane forecaster William Gray said a fading El Niño will
help produce more hurricane activity this year than in 1997.
However, storm totals should only constitute what is considered
average for the past 50 years, he said. The faster-than-expected
disappearance of the strongest El Niño on record will eliminate a factor
that works against hurricane formation. The El Niño phenomenon caused
last year's season to be unusually quiet.
Gray's third report of the 1998 season calls for 10 tropical storms to
form in the Atlantic Basin through Nov. 30. Six tropical storms will
evolve into hurricanes and two will go on to become intense hurricanes
with winds of 111 mph or more.
Gray and his team initially predicted nine tropical storms, five
hurricanes and two major or Andrew-type intense hurricanes in their initial
report last December and increased their forecast total of storms and
hurricanes to 10 and six, respectively, in an early April update.
On average, 9.3 tropical storms, 5.8 hurricanes and 2.2 intense
hurricanes form annually.
"The basis of our forecast is that the El Niño, the strongest one
we've ever had by nearly a factor of two, is fading out fast and should be
dissipated by the start of the active part of the hurricane season in
mid-August," Gray said. "We may even have some slightly cool water in the
eastern equatorial Pacific by the height of the hurricane season in
September. So we don't think El Niño will be a significant inhibiting
factor this year."
Last year's hurricane activity was suppressed by what turned out to
be the strongest El Niño ever recorded during the peak hurricane months
of August to October. In today's update, Gray and his colleagues predict
that the fading of El Niño, plus other climate changes favorable to storm
formation, will combine to produce a season with more hurricane activity
than last year.
"We think we'll see a slightly above-average number of named
storms, slightly above average for the hurricanes and slightly below
average for major storms," Gray said. "So I would characterize it as an
average season in terms of the last 48 years."
However, Gray said, taken in light of the "remarkable downturn" in
storms evident in the period from 1970 to 1994, this year's numbers
represent activity busier than what has been seen during most years in
recent decades.
While the El Niño phenomenon sometimes is followed by a
condition in the eastern Pacific called La Niña, Gray said data suggest that
if the cold water does appear in the eastern equatorial Pacific, it will
probably do so too late to have much effect on the hurricane season, which
ends by November.
Several climatic factors beside the fading of El Niño appear
favorable to formation of storms this year. These include above-average
sea surface temperatures in the tropical north Atlantic and a ridge of
eastern Atlantic air near the Azores Islands in the North Atlantic that has
remained weak since last October. This reduced high pressure causes
weaker East Atlantic trade winds and is more favorable for hurricane
development in the following season, according to Gray.
One of the uncertainties in the 1998 forecast involves rainfall in the
Western Sahel region of Africa. When this region is wetter than normal, it
typically promotes hurricane formation and the season's net hurricane
activity will be increased. When dryer than normal conditions are present
in this region, hurricane activity typically is inhibited.
Although information on rainfall in the Sahel region of West Africa
isn't clear, "We're pretty sure it's not going to be dry this year," Gray
said. Recent drier-than-average conditions in this region were brought
on by El Niño and therefore should not be considered an indication that
1998 hurricane activity will be greatly reduced, according to the team's
report.
As of the end of May, the only negative factor for hurricane
formation is the Quasi-Biennial Oscillation, the equatorial stratospheric
winds at 68,000 to 75,000 feet that are expected to blow from an easterly
direction this summer. This easterly flow tends to inhibit hurricane
development. When the QBO blows in a westerly direction, there is
typically 50 percent to 75 percent more hurricane activity, according to
Gray.
Throughout the season Gray and research team members Chris
Landsea at the National Oceanic and Atmospheric Administration
Hurricane Research Division in Miami, Fla., and Colorado State faculty
members Paul Mielke and Kenneth Berry also take into account
temperature and pressure readings in West Africa, Caribbean Sea-level
pressure readings, temperature readings above Singapore at about 54,000
feet and tropospheric winds at 40,000 feet.
Gray's hurricane forecasts - issued annually in early December,
April, June and August - do not predict landfall and apply only to the
Atlantic Basin, the area encompassing the Atlantic Ocean, Caribbean Sea
and Gulf of Mexico.
Although El Niño suppressed hurricane activity last year, statistics
show that the period between 1995-1997 still was the busiest three-year
period for hurricane activity on record. The three-year span generated 39
named storms, 23 hurricanes (12 of which were intense) and 107 hurricane
days.
Based on that record, Gray theorizes that the Atlantic Basin is
entering an era that will see many decades of increased hurricane activity
and which will include particularly intense or major hurricanes.
HURRICANE FORECASTS--1998 SEASON
TODAY'S 4/98 12/97
1. Named Storms (9.3)* 10 10 9
2. Named Storm Days (46.9) 50 50 40
3. Hurricanes (5.8) 6 6 5
4. Hurricane Days (23.7) 25 20 20
5. Intense Hurricanes (2.2) 2 2 2
6. Intense Hurricane Days (4.7) 4 4 3
7. Hurricane Destruction Potential (70.6)** 70 65 50
8. Net Tropical Cyclone Activity (100%) 100% 95% 90%
'97 ACTUAL 8/97 6/97 4/97 12/96
1. Named Storms (9.3) 7 11 11 11 11
2. Named Storm Days (46.9) 28 45 55 55 55
3. Hurricanes (5.8) 3 6 7 7 7
4. Hurricane Days (23.7) 10 20 25 25 25
5. Intense Hurricanes (2.2) 1 2 3 3 3
6. Intense Hurricane Days (4.7) 2.2 3 5 5 5
7. Hurricane Destruction Potential (70.6) 26 60 75 75 75
8. Net Tropical Cyclone Activity (100%) 54 100% 110% 110% 110%
* Number in ( ) represents average year totals based on 1950-1990
** Hurricane Destruction Potential measures a hurricane's potential for
wind- and ocean-surge damage. Tropical Storm, Hurricane and Intense
Hurricane Days are four, six-hour periods where storms attain wind speeds
appropriate to their category on the Saffir-Simpson scale.
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