The Atlantic hurricane season starts in just over a week, and long-range
models are already pointing to the possibility that the Western
Caribbean will be capable of brewing the season's first "Invest" during
the first week of June. But so far, the major hurricane forecasting
groups are not impressed with this season's potential to be an active
one. They are calling for 2014 to be a below average to near-average
year for the Atlantic.
NOAA's prediction, issued this Thursday morning,
forecasts
a 50% chance of a below-normal season, a 40% chance of an near-normal
season, and only a 10% chance of an above-normal season. They predict a
70% chance that there will be 8 - 13 named storms, 3 - 6 hurricanes, and
1 - 2 major hurricanes, with an Accumulated Cyclone Energy (ACE) 40% -
100% of the median. If we take the midpoint of these numbers, NOAA is
calling for 10.5 named storms, 4.5 hurricanes, 1.5 major hurricanes, and
an ACE index 70% of normal. This is below the 1981 - 2010 average of 12
named storms, 6 hurricanes, and 3 major hurricanes. Hurricane seasons
during the active hurricane period 1995 - 2013 have averaged 15 named
storms, 8 hurricanes, and 4 major hurricanes, with an ACE index 151% of
the median.
NOAA cites three key factors influencing their forecast for a below-normal to near-normal hurricane season:
1)
An El Niño event is predicted for the summer and fall, which is
expected to bring strong wind shear-inducing upper-level winds over the
Tropical Atlantic. Vertical wind shear during the past 30 days was
stronger than average across much of the Main Development Region (MDR)
for hurricanes, from the coast of Africa to the Caribbean. Sinking air
at mid-and upper-levels was also stronger than average. The development
of El Niño would mean a likely continuation of these non-conducive
conditions, and both versions of NOAA's long-range CFS model are
predicting enhanced vertical wind shear across the western MDR during
August-September-October 2014. Strong vertical wind shear and sinking
motion, linked to a rare jet stream pattern of record strength,
were key suppressing factors during the unexpectedly quiet 2013 Atlantic hurricane season.2)
Sea Surface Temperatures (SSTs) are near average in the MDR. Many
long-range dynamical computer forecast models are predicting that SSTs
in the MDR will remain near- or below-average throughout the hurricane
season.
3) We are in an active hurricane period that began in
1995, and this positive phase of the Atlantic Multi-decadal Oscillation
(AMO) may act to keep hurricane activity higher than it would otherwise
be.
Colorado State predicts a below-average hurricane season: 9 named storms
A below-average Atlantic hurricane season is on tap for 2014, according to the
seasonal hurricane forecast
issued April 10 by Dr. Phil Klotzbach and Dr. Bill Gray of Colorado
State University (CSU). The CSU team is calling for 9 named storms, 3
hurricanes, and 1 intense hurricane, and an
Accumulated Cyclone Energy
(ACE) of 55, a little more than half of average. The forecast calls for
a below-average chance of a major hurricane hitting the U.S., both
along the East Coast (20% chance, 31% chance is average) and the Gulf
Coast (19% chance, 30% chance is average). The risk of a major hurricane
in the Caribbean is also below average, at 28% (42% is average.)
CSU's Analogue years: 2002, 1997, 1965, 1963, and 1957The
CSU team picked five previous years when atmospheric and oceanic
conditions were similar to what they expect for this year: moderate El
Niño conditions, neutral to slightly cool sea surface temperatures in
the tropical Atlantic, and a positive phase of the Atlantic
Multi-decadal Oscillation (AMO). Those five years were
2002, which featured two major hurricanes that got their names retired:
Lili and
Isidore; 1997, a quiet year with only 8 named storms and 3 hurricanes;
1965, a quiet year with only 6 named storms (but one of these was a real doozy--
Hurricane Betsy, which struck Louisiana as a Category 3 storm;)
1963, with 9 named storms and 7 hurricanes, including Cuba's deadliest hurricane of all-time:
Hurricane Flora (8,000 killed); and
1957, a below-average year with 8 named storms and 2 major hurricanes, including June's deadly
Hurricane Audrey,
which was re-analyzed as a Category 3 storm this year. The average
activity during these five analogue years was 9 named storms, 4
hurricanes, and 2 major hurricanes. The CSU team will issue an updated
forecast on Monday, June 2, 2014.
TSR predicts a near-average hurricane season: 12 named storms
The April 7 forecast for the 2014 Atlantic hurricane season made by British private forecasting firm
Tropical Storm Risk, Inc. (TSR) calls for a near-average season with 12 named storms, 5 hurricanes, 2 intense hurricanes, and an
Accumulated Cyclone Energy
(ACE) of 75. The long-term averages for the past 64 years are 11 named
storms, 6 hurricanes, 3 intense hurricanes, and an ACE of 102. TSR rates
their skill level as modest for these April forecasts: 7 - 15% higher
than a "no-skill" forecast made using climatology. They project that 3
named storms will hit the U.S., with 1 of these being a hurricane. The
averages from the 1950-2013 climatology are 3 named storms and 1
hurricane hitting the United States. TSR rates their skill at making
these April forecasts for U.S. landfalls just 5% - 8% higher than a
"no-skill" forecast made using climatology. In the Lesser Antilles
Islands of the Caribbean, TSR projects one named storm and no hurricanes
in 2014. Climatology is 1.1 named storms and 0.5 hurricanes.
TSR's
two predictors for their statistical model are the forecast July -
September trade wind speeds over the Caribbean and tropical North
Atlantic, and the forecast August - September 2013 sea surface
temperatures (SSTs) in the tropical North Atlantic Main Development
Region (MDR) for hurricanes. Their model is calling for SSTs 0.32°C
below average and trade winds 1 m/s stronger than average during these
periods; both of these factors should act to decrease hurricane and
tropical storm activity. The July-September 2014 trade wind prediction
is based on an expectation of moderate El Niño conditions in
August-September 2014. TSR will issue an updated forecast on May 27,
2014.
Penn State predicts a below-average hurricane season: 9 named stormsA statistical model by Penn State's Michael Mann, alumnus Michael Kozar, and researcher Sonya Miller
is calling for a quiet Atlantic hurricane season
with 9.3 named storms, plus or minus 3 storms. Their prediction was
made using statistics of how past hurricane seasons have behaved in
response to sea surface temperatures (SSTs), the El Niño/La Niña
oscillation, the North Atlantic Oscillation (NAO), and other factors.
The statistical model assumes that the mid-May 2014 0.29°C above average
SSTs in the MDR will persist throughout hurricane season, a moderate El
Niño will be in place, and the North Atlantic Oscillation (NAO) will be
near average.
The PSU team has been making Atlantic hurricane
season forecasts since 2007, and these predictions have done pretty
well, except for in 2012, when an expected El Niño did not materialize.
They were the only major forecast group that issued a successful 2013
Atlantic hurricane season forecast.
2007 prediction: 15 named storms, Actual: 15
2009 prediction: 12.5, named storms, Actual: 9
2010 prediction: 23 named storms, Actual: 19
2011 prediction: 16 named storms, Actual: 19
2012 prediction: 10.5 named storms, Actual: 19
2013 prediction: 16 named storms, Actual: 14
UK Met Office predicts a below-average hurricane season: 10 named stormsThe
UKMET office forecast for the 2014 Atlantic hurricane season,
issued May 16, calls for below-average activity, with 10 named storms, 6
hurricanes, and an ACE index of 84. In contrast to the statistical
models relied upon by CSU, TSR, PSU, and NOAA, the UKMET forecast is
done strictly using two dynamical global seasonal prediction systems:
the Met Office GloSea5 system and ECMWF system 4. Their forecasts for
the past two years have not verified well:
2012 prediction: 10 named storms, ACE index of 90; Actual: 19 named storms, ACE index of 123
2013 prediction: 14 named storms, 9 hurricanes, ACE index of 130; Actual: 14 named storms, 2 hurricanes, ACE index of 31
NOAA predicts an above-normal or near-normal Eastern Pacific hurricane season: 17 named stormsAs is usually the case when an El Niño event is threatening,
NOAA's pre-season prediction for the Eastern Pacific hurricane season,
issued on May 22, is calling for an active season. NOAA expects there
to be 14 - 20 named storms, 7 - 11 hurricanes, 3 - 6 major hurricanes,
and an ACE index 95% - 160% of the median. The mid-point of these ranges
gives us a forecast for 17 named storms, 9 hurricanes, and 4.5 major
hurricanes, with an ACE index 127.5% of average. The 1981 - 2010
averages for the Eastern Pacific hurricane season are 15 named storms, 8
hurricanes, and 4 major hurricanes. The outlook calls for a 50% chance
of an above-normal season, a 40% chance of a near-normal season, and a
10% chance of a below-normal season. El Niño decreases the vertical wind
shear over the tropical Eastern Pacific, favoring the development of
more and stronger tropical cyclones. Since 1995 the Eastern Pacific has
been in an era of low activity for hurricanes, but this pattern will be
offset in 2014 by the impacts of El Niño.
NOAA predicts a near-normal or above-normal Central Pacific hurricane seasonNOAA's pre-season prediction for the Central Pacific hurricane season,
issued on May 22, calls for a near-normal or above-normal season, with 4
-7 tropical cyclones. An average season has 4 - 5 tropical cyclones,
which include tropical depressions, tropical storms, and hurricanes. The
outlook calls for a 40% chance of a near-normal season, a 40% chance of
an above-normal season, and a 20% chance of a below-normal season. El
Niño decreases the vertical wind shear over the tropical central
Pacific, favoring the development of more and stronger tropical
cyclones. Since 1995 the central Pacific has been in an era of low
activity for hurricanes, but this pattern will be offset in 2014 by the
impacts of El Niño. Hawaii is the primary land area affected by Central
Pacific tropical cyclones.
Even a quiet hurricane season can be devastatingQuiet
hurricane seasons with below-average activity can still produce major
hurricanes that cause massive devastation. The five seasons that CSU
lists as analogue years for 2014 produced five hurricanes that had their
names retired, including one that killed 8,000 people in Cuba (Flora of
1963) and one that killed over 400 people in Texas and Louisiana
(Audrey of 1957.) Even if an El Niño does develop this year, that
doesn't mean it will be a quiet season. Recall the El Niño year of 2004,
when four major hurricanes pounded the U.S.--Ivan, Charlie, Jeanne, and
Frances. Those of you in Hurricane Alley should
prepare for the 2014 season the same way you would for a predicted hyperactive season, and
be ready for the Storm of the Century to hit your location.
Jeff Masters