The prediction for 2009's Atlantic Hurricane season follows, courtesy
of WeatherUnderground:


Average hurricane season foreseen by CSU and NOAA

Posted by: JeffMasters, 4:45 PM GMT on June 02, 2009
A near-average Atlantic hurricane season is on tap for 2009, according
to the seasonal hurricane forecast issued June 2 by Dr. Phil Klotzbach
and Dr. Bill Gray of Colorado State University (CSU). The CSU team is
calling for 11 named storms, 5 hurricanes, and 2 intense hurricanes,
and an Accumulated Cyclone Energy (ACE) 88% of average. Between 1950 -
2000, the average season had 10 named storms, 6 hurricanes, and 2
intense hurricanes. But since 1995, the beginning of an active
hurricane period in the Atlantic, we've averaged 15 named storms, 8
hurricanes, and 4 intense hurricanes per year. The new forecast is a
step down from their April forecast, which called for 12 named storms,
6 hurricanes, and 2 intense hurricanes. The new forecast calls for a
near-average chance of a major hurricane hitting the U.S., both along
the East Coast (28% chance, 31% chance is average) and the Gulf Coast
(28% chance, 30% chance is average). The Caribbean is also forecast to
have an average risk of a major hurricane.

The forecasters cited several reasons for an average season:

1) Sea surface temperature (SST) anomalies in the tropical Atlantic
are quite cool. In fact, these SST anomalies are at their coolest
level since July 1994. Cooler-than-normal waters provide less heat
energy for developing hurricanes. In addition, an anomalously cool
tropical Atlantic is typically associated with higher sea level
pressure values and stronger-than-normal trade winds, indicating a
more stable atmosphere with increased levels of vertical wind shear
detrimental for hurricanes. Substantial cooling began in November 2008
(Figure 1), primarily due to a stronger than average Bermuda-Azores
High that drove strong trade winds. These strong winds increased the
mixing of cool waters to the surface from below, and caused increased
evaporational cooling.

2) Hurricane activity in the Atlantic is lowest during El Niño years
and highest during La Niña or neutral years. This occurs because El
Niño conditions bring higher wind shear over the tropical Atlantic.
The CSU team expects the current neutral conditions may transition to
El Niño conditions (70% chance) by this year's hurricane season. I
discussed the possibility of a El Niño conditions developing this year
in a blog posted Friday

Analogue years
The CSU team picked five previous years when atmospheric and oceanic
conditions were similar to what we are seeing this year: neutral to
slightly warm ENSO conditions, slightly below-average tropical
Atlantic SSTs, and above-average far North Atlantic SSTs during April-
May. Those five years were 2002, which featured Hurricane Lili that
hit Louisiana as a Category 1 storm; 2001, featuring Category 4 storms
Michelle, which hit Cuba, and Iris, which hit Belize; 1965, which had
Category 3 Betsy that hit New Orleans; 1960, which had two Category 5
hurricanes, Ethyl and Donna; and 1959, which had Category 3 Hurricane
Gracie, which hit South Carolina. The mean activity for these five
years was 10 named storms, 6 hurricanes, and 2 intense hurricanes,
almost the same as the 2009 CSU forecast.

How accurate are the June forecasts?
The June forecasts by the CSU team have historically offered a skill
of 20 - 30% higher than a "no-skill" forecast using climatology
(Figure 2). This is a decent amount of skill for a seasonal forecast,
and these June forecasts can be useful to businesses such as the
insurance industry and oil and gas industry that need to make bets on
how active the coming hurricane season will be. This year's June
forecast uses the same formula as last year's June forecast, which did
quite well predicting the 2008 hurricane season (prediction: 15 named
storms, 8 hurricanes, 4 intense hurricanes; observed: 16 named storms,
8 hurricanes, 5 intense hurricanes). An Excel spreadsheet of their
forecast skill (expressed as a mathematical correlation coefficient)
show values from 0.44 to 0.58 for their June forecasts, which is

NOAA's 2009 hurricane season forecast
The National Oceanic and Atmospheric Administration (NOAA), issued its
2009 Atlantic hurricane season forecast on May 21. NOAA anticipates
that an average season it most likely, giving a 50% chance of a near-
normal season, 25% chance of an above-normal season, and a 25% chance
of a below-normal season. They give a 70% chance that there will be 9
- 14 named storms, 4 - 7 hurricanes, 1 - 3 major hurricanes, and an
Accumulated Cyclone Energy (ACE) in the 65% - 130% of normal range.
The forecasters cited the following main factors that will influence
the coming season:

1) We are in an active period of hurricane activity that began in
1995, thanks to a natural decades-long cycle in hurricane activity
called the Atlantic Multidecadal Oscillation (AMO).

2) There will either be an El Niño event or neutral conditions in the
Equatorial Eastern Pacific. An El Niño event should act to reduce
Atlantic hurricane activity. However, our skill at predicting an Niño
in late May/early June is poor, so there is high uncertainty about how
active the coming hurricane season will be.

3) Cooler-than-average SSTs are currently present in the eastern
tropical Atlantic. These cool SSTs are forecast to persist through
into August-September-October (ASO). ASO SSTs in the eastern tropical
Atlantic have not been below average since 1997. Cooler SSTs in that
region are typically associated with a reduction in Atlantic hurricane

Thus, they expect that even though we are in an active hurricane
period, the presence of an El Niño or cool SSTs in the eastern
Atlantic could easily suppress activity, making a near-average season
the most likely possibility. They note that two promising computer
models, the NOAA CFS model and the European Center for Medium-Range
Weather Forecasts (ECMWF) Global Climate Model System 3, both forecast
the possibility of a below-average hurricane season.

2009 Atlantic hurricane season forecast from Tropical Storm Risk, Inc.
The British private forecasting firm Tropical Storm Risk, Inc. (TSR),
issued their most recent 2009 Atlantic hurricane season forecast in
April, when they called for an active year: 15 named storms, 7.8
hurricanes, and 3.6 intense hurricanes. Their updated forecast is due
out out June 4, and I expect their numbers will fall more in line with
NOAA's and CSU's.

Air France crash
The Air France Flight 447 A330 aircraft that disappeared over the mid-
Atlantic Ocean yesterday definitely crossed through a thunderstorm
complex near the Equator, according to a detailed meteorological
analysis by Tim Vasquez. He concludes that "the A330 would have been
flying through significant turbulence and thunderstorm activity for
about 75 miles (125 km), lasting about 12 minutes of flight time" but
that "complexes identical to this one have probably been crossed
hundreds of times over the years by other flights without serious
incident". See also the excellent CIMSS satellite blog for more images
and analysis of the weather during the flight.

Invest 92
NHC is tracking a storm near the Azores Islands (Invest 92L) that is
probably the remnants of the core of an extratropical cyclone that
closed off some warm air at the center. The system has developed some
heavy thunderstorm activity near its center, making this a hybrid
storm. However, with ocean temperatures near 62°F (16°C), this storm
has little chance of becoming a named subtropical storm.

Jeff MastersPrediction for 2009's Atlantic Hurricane season