There is a moderate (50%) likelihood that the upcoming North Atlantic hurricane season will have normal levels of overall activity, according to a consensus of scientists at the National Oceanic and Atmospheric Administration's (NOAA) Climate Prediction Center (CPC), National Hurricane Center (NHC) and Hurricane Research Division (HRD).  Given the anticipated conditions over the tropical North Atlantic, the 2001 hurricane season will likely have less overall activity than five of the last six seasons (the exception being the inactive 1997 season), but more activity than most of the relatively quiet 1970-1994 period. On average, seasons with normal levels of activity have 1-2 landfalling hurricanes in the U.S., and 1 landfalling hurricane in the region around the Caribbean Sea.

DISCUSSION

1. Expected Level of Overall Activity - Normal

Our forecast is for a 50% chance of normal levels of activity during the 2001 Atlantic hurricane season, a 25% chance of above-normal activity and a 25% chance of below-normal activity.  Using the "Accumulate Cyclone Energy" [ACE] index as the basis for measuring overall activity [(see Background Information)], the historical record indicates that 55% of seasons with normal levels of activity have featured 8-11 tropical storms, 67% have featured 5-7 hurricanes, and 67% have featured 2-3 major hurricanes [categories 3-4-5 on the Saffir-Simpson scale].   Only 44% of all seasons with normal levels of activity feature the combination of 8-11 tropical storms, 5-7 hurricanes and 2-3 major hurricanes.  Thus, while it is reasonable to expect 8-11 tropical storms, 5-7 hurricanes and 2-3 major hurricanes this season, the season can certainly feature normal levels of activity without all three of these criteria being met.

Based on past historical data a season with normal levels of activity also averages 1-2 landfalling hurricanes in the continental United States and about one hurricane in the region around the Caribbean Sea.

2. Expected Climate Conditions- La Niña/ El Niño not expected to play important role

The recent, long-running La Niña has dissipated, but its related climate patterns persist at this time. However, these patterns are expected to dissipate over the next few months, and are unlikely to favor above-normal activity this season as they did during the past three (1998-2000) seasons.  Instead, the primary global and regional climate conditions guiding this year’s outlook are decadal-scale patterns of enhanced tropical rainfall on a global scale, and average to slightly above-average Atlantic sea-surface temperatures during August-October. Similar conditions contributed to the active decades of the 1950’s and 1960’s, and to the dramatic upturn in hurricane activity observed since 1995. A secondary climate factor, easterly winds in the lower stratosphere, is expected to provide a slightly suppressing influence on overall Atlantic hurricane activity this season.

The above combination of climate conditions indicates a 50% chance of normal levels of activity this hurricane season, a 25% chance of above-normal activity and a 25% chance of below-normal activity.

3. Uncertainties in the Outlook

The main uncertainties in this outlook are related to uncertainties in forecasting the transition from La Niña to El Niño conditions, and the timing and magnitude of the changes in the related atmospheric circulation and tropical convection patterns. At this time, however, we anticipate that the La Niña- related atmospheric circulation and tropical convection patterns will dissipate by the August-October peak in hurricane activity. Also, we do not foresee the development of an El Niño strong enough to be a dominant factor in this year’s hurricane season. We will continue to closely monitor these climate conditions prior to the release of an updated outlook in early August, which is the beginning of the active portion of the Atlantic hurricane season.

Background Information

CAUTIONARY NOTES

1) This Outlook represents our best estimate for the expected overall level of activity for the Atlantic basin.  No outlook can give certainty as to whether or not a particular locality will be impacted by a hurricane in any given year.  Residents and government agencies of coastal or near-coastal regions should always maintain hurricane preparedness efforts, regardless of the overall outlook for a given year.

2) Far more damage can be done by one major hurricane hitting a heavily populated area than by several hurricanes hitting sparsely populated areas or, of course, not making landfall at all.  Because of this, hurricane-spawned disasters can occur even in years with normal (or below-normal) levels of activity.  Examples of years with normal levels of activity that featured extensive hurricane damage and numerous fatalities include 1960 (Hurricane Donna), 1979 (Hurricanes David and Frederic), and 1985 (Hurricanes Elena, Gloria and Juan). Moreover, the nation’s most damaging hurricane, Andrew in 1992, occurred during a season with below-normal levels of activity.

ACKNOWLEDGMENTS

This outlook is not designed to compete with hurricane outlooks issued by groups outside NOAA.  We gratefully acknowledge the pioneering research of Dr. William Gray and others, which has significantly increased scientific understanding of the links between various climate factors (particularly the El Niño/ La Niña cycle) and the atmospheric circulation features that affect Atlantic hurricane activity.  We also acknowledge the leading role that Dr. Gray and colleagues at the Colorado State University have played in developing and providing seasonal forecasts of Atlantic basin hurricane activity.

CONTACTS

Dr. Lixion Avila, Meteorologist, National Hurricane Center; ph: 305-229-4470; lixion@nhc.noaa.gov

Dr. Gerald Bell, Meteorologist, Climate Prediction Center: ph: 301-763-8000 x 7536; gbell@ncep.noaa.gov

Dr. Muthuvel Chelliah, Physical Scientist, Climate Prediction Center: ph: 301-763-8000 x 7546; mchelliah@ncep.noaa.gov

Mr. Stanley Goldenberg, Meteorologist, Hurricane Research Division: ph: 305-361-4362;goldenberg@aoml.noaa.gov

Dr. Vernon Kousky, Meteorologist, Climate Prediction Center:
ph: 301-763-8000 x 7539; vkousky@ncep.noaa.gov

Dr. Christopher Landsea, Meteorologist, Hurricane Research Division: ph: 305-361-4357; landsea@aoml.noaa.gov

Dr. Richard Pasch, Meteorologist, National Hurricane Center; ph: 305-229-4411; richard@nhc.noaa.gov