Uncertainties in the Outlook, and a look back at 2007. Dr. Gerry Bell, Meteorologist; Gerry.Bell@noaa.gov Dr. Richard Pasch, Hurricane Specialist; Richard.J.Pasch@noaa.gov Another uncertainty is the possibility of lesser climate factors also influencing the seasonal activity. Atlantic hurricane seasons exhibit prolonged periods lasting decades of generally above-normal or below-normal activity. The regional atmospheric circulation anomalies that contribute to these long-period fluctuations in hurricane activity are strongly linked to the tropics-wide multi-decadal signal (Bell and Chelliah, 2006). Bull. The names Jessica, Micah, Sally, Teddy, Vicky and Wilfred were used for the first (and only, in the cases of Micah and Teddy) time this year. SSTs are already well above average in that region and along the west coast of northern Africa. The expected conditions during the 2008 Atlantic hurricane season are related to two main climate signals: 1) the continuation of conditions (called the multi-decadal signal) that have been conducive to above-normal Atlantic hurricane activity since 1995 , including above-normal sea-surface temperatures in the eastern tropical Atlantic Ocean, and 2) a possible La Ni�a influence or ENSO-neutral conditions during the peak months (August-October) of the season. In the latest ENSO Diagnostics Discussion released 8 May 2008, NOAA forecasters stated that La Ni�a has weakened since February, and that a transition to ENSO-neutral conditions is possible during June-July just prior to the peak months of the Atlantic hurricane season. These fluctuations in hurricane activity result almost entirely from differences in the number of hurricanes and major hurricanes forming from tropical storms first named in the Main Development Region (MDR), which spans the tropical Atlantic Ocean and Caribbean Sea between 30oW-87.5oW and 10oN-21.5oN (Goldenberg et al. 12-16 named storms, Three major sources of uncertainty in the seasonal outlooks. These include the three El Ni�o years (1997, 2002, and 2006) and the 2007 season. First, despite a strengthening La Ni�a during ASO 2007, the typical La Ni�a signal in the upper-tropospheric circulation was notably absent across the tropical North Pacific and MDR. As discussed by Gray (1984), La Ni�a favors more Atlantic hurricanes and El Ni�o favors fewer hurricanes. 2. This circulation led to increased vertical wind shear and anomalous mid-level sinking motion across the central and western MDR, two factors known to inhibit hurricane formation. 2008 WMHB Atlantic hurricane season (Sandy156), 2020 North Indian Ocean cyclone season (Olo72). Bell, G. D., and Co-authors 2007: The 2006 Atlantic Hurricane Season: A Climate Perspective. The likely (60%-70% chance) ACE range for the 2008 Atlantic hurricane season reflects three inter-related sources of uncertainty: 1) When La Ni�a will dissipate, 2) the likelihood that the current La Ni�a patterns of tropical convection and winds will persist into ASO, even if La Ni�a dissipates, and 3) the likely strength of those patterns. They do not represent the total ranges of activity seen in those past seasons. Most models are predicting ENSO-neutral conditions (neither El Ni�o nor La Ni�a) during the summer, with sea-surface temperature anomalies in the central and east-central equatorial Pacific between -0.5oC to 0.5oC. The current active hurricane era began in 1995. State of the Climate in 2006. On April 22, 2009, at the 31st Session of the RA IV Hurricane Committee, the World Meteorological Organization retired the names Farrah, Lili, Micah, Nana, Omar, Teddy, and Hussein from their rotating name lists due to the number of deaths and damage they caused, and they will not be used again for another Atlantic hurricane. A. M. Waple and J. H. Lawrimore, Eds. DISCUSSION Most of the 2008 activity is expected to take place during August through October (ASO), the peak months of the Atlantic hurricane season. Realtime monitoring of tropical East Pacific conditions. This outlook is based on the analysis and prediction of two main climate signals: Second, that upper-level trough was enhanced in association with a very persistent ridge over eastern North America. Another uncertainty is the possibility of lesser climate factors also influencing the seasonal activity. A. M. Waple and J. H. Lawrimore, Eds. An ACE range 100%-210% of the median While an above-normal season is most likely (65% chance), there is a significant 25% chance of a near-normal season and a 10% chance of a below-normal season. Stanley Goldenberg, Meteorologist; Stanley.Goldenberg@noaa.gov