Forecast On The Internet In The Afternoon
Friday, April 4, 1997
RESEARCH TEAM STICKS WITH PREDICTION OF ABOVE-AVERAGE HURRICANE
YEAR; COLORADO STATE'S GRAY SAYS MORE ACTIVE STORM PERIOD BREWING
NOTE: Forecast totals in chart form attached. Gray's
complete forecast plus related research and press
releases available on the Internet at address listed
above. A taped interview with Gray is available at
(970) 491-1525.
FORT COLLINS--Colorado State University's team of hurricane
forecasters is sticking with its prediction of an above-average
hurricane year in 1997, with seven hurricanes and three intense
hurricanes.
The noted team, led by Professor William Gray, released an
updated forecast today for 1997, that, if it holds true, would
make this year the third consecutive active hurricane season. In
fact, if this forecast bears out, the period from 1995-97 would
become the most-active, three-year hurricane span in history.
That directly contrasts 1991-94, the most inactive four-year
period in history.
Gray says this recent active trend could signal the start of
a return of more tropical storms and hurricanes, particularly
more intense hurricanes.
"More and more it's looking like we have left a period of
lessened hurricane activity and we could be seeing a basic change
in the long-term global circulation patterns that could lead to
more hurricanes," Gray said. "What's particularly disturbing is
this change would likely increase the number of major hurricanes.
This is an area we need to look at to help determine what might
be in our future."
In this forecast--the second of four the team will issue for
the 1997 season--Gray and his research team predict 11 tropical
storms will form. Of those, the team says seven will become
hurricanes, and of those, three will become intense, or major,
hurricanes.
These major storms, which cause 75 percent of all storm-
spawned damage, are characterized by sustained winds of at least
111 mph. Major storms fall into Category 3,4 and 5 hurricanes on
the Saffir-Simpson scale. Hugo and Andrew were both Category 4
hurricanes when they made landfall.
In comparison, storms categorized simply as hurricanes have
sustained winds of 74 mph or greater.
In the research team's first forecast (Dec. 1996) for the
1997 hurricane season, Gray and his colleagues predicted that a
total of 11 tropical storms would form between June 1 and
Nov. 30, 1997. From those storms, seven hurricanes will evolve
and three will become major hurricanes. On average, 9.3 tropical
storms, 5.8 hurricanes and 2.1 major hurricanes form annually.
Gray's hurricane forecasts--issued in December, April, June
and August--do not predict landfall and apply only to the
Atlantic Basin, the area including the Atlantic Ocean, Caribbean
Sea and Gulf of Mexico.
Gray and his research team base their forecasts on a number
of global weather features. In today's forecast, Gray continues
to point to two factors that indicate above-average activity.
First, Gray and his team predict there will be no El Ni、o--a
period of warmer than normal water temperatures off the coast of
Peru. When El Ni、o is in place, it produces upper-level westerly
winds at 40,000 feet in the tropical Atlantic Ocean. This helps
shear off hurricane development. Gray predicts La Ni、a conditions
will be in place--meaning temperatures off the coast of Peru will
be slightly cooler than average--which will promote hurricane
activity.
In addition, the equatorial stratospheric winds at
68,000-75,000 feet--known as Quasi-Biennial Oscillation--will
blow from a relative westerly direction. This tends to promote
the formation of hurricanes--particularly major hurricanes. Gray
also relied on these factors heavily in issuing his forecast in
December.
Gray and his colleagues also look at other weather signals
around the globe. For example, Gray says that temperature
readings of air above Singapore at the 100 millibar level--or
about 54,000 feet--continue to be colder than usual, which is a
precursor for above-normal hurricane activity for the Atlantic
Ocean in the six-month period.
Gray and research team members Chris Landsea, a Colorado
State graduate and researcher at the NOAA's Hurricane Research
Laboratory in Miami, Fla., and John Knaff, Paul Mielke and
Kenneth Berry, all of Colorado State, rely primarily on the
following factors to issue their forecasts: the strength or
weakness of El Ni、o; the direction of equatorial stratospheric
winds at 68,000-75,000 feet; rainfall in the West African Sahel
region; temperature and pressure readings in West Africa;
Caribbean Sea-level pressure readings; Atlantic sea-surface
temperature readings; and tropospheric winds at 40,000 feet. The
research team also added pressure readings in the northeast
Atlantic to the forecast.
GRAY RESEARCH TEAM'S HURRICANE FORECAST FOR '97 SEASON
TODAY'S FORECAST 12/96
1. Named Storms (9.3) 11 11
2. Named Storm Days (46.1) 55 55
3. Hurricanes (5.7) 7 7
4. Hurricane Days (23) 25 25
5. Intense Hurricanes (2.1) 3 3
6. Intense Hurricane
Days (4.5) 5 5
7. Hurricane Destruction
Potential (68.1) # 75 75
8. Net Tropical Cyclone
Activity (100%) 110 110
'96 ACTUAL 8/96 6/96 4/96 11/95
1. Named Storms (9.3) 13 11 10 11 8
2. Named Storm Days (46.1) 78 50 45 55 40
3. Hurricanes (5.7) 9 7 6 7 5
4. Hurricane Days (23) 45 25 20 25 20
5. Intense Hurricanes (2.1) 6 3 2 2 2
6. Intense Hurricane
Days (4.5) 13 4 5 5 5
7. Hurricane Destruction
Potential (68.1) # 135 70 60 75 50
8. Net Tropical Cyclone
Activity (100%) 198 105 95 105 85
( ) 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.
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