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HOME > Expert Assessments > Atlantic Hurricane Outlook

June-November Atlantic Hurricane Outlook:

Issued 27 May 1999

There is a strong likelihood of above-average tropical storm and hurricane activity over the North Atlantic basin during the June-November 1999 hurricane season, in response to an expected continuation of ongoing La Niņa conditions and its associated atmospheric circulation and tropical rainfall patterns, according to a consensus reached by scientists at the National Oceanic and Atmospheric Administration's (NOAA) Climate Prediction Center (CPC), National Hurricane Center (NHC) and Hurricane Research Division (HRD). There is also a strong likelihood of at least three major hurricanes this year. Most of this activity is expected to occur during the peak three months (August-October) of the season. An updated outlook will be issued in early August.

This Outlook should be used as a guide of overall expected activity for the Atlantic basin. The Outlook does not give any indication of whether a particular locality will be impacted by a tropical storm or hurricane during 1999. Residents and government agencies of coastal or near-coastal regions should always maintain normal hurricane preparedness efforts regardless of the overall outlook for a given year.

La Niņa refers to cooler than average sea-surface temperatures across the central and eastern tropical Pacific. In combination with these oceanic conditions, the present pattern of tropical rainfall is dominated by above-normal rainfall across Indonesia and the eastern Indian Ocean, and by a near-absence of rainfall across the eastern equatorial Pacific. This pattern of tropical rainfall is associated with atmospheric circulation features which often favor an active hurricane season. It appears at this time that the ongoing La Niņa episode, and associated tropical rainfall and atmospheric circulation patterns, will persist through the current hurricane season.

If, as expected, these atmospheric conditions persist through the season, then they will likely favor an active hurricane season by influencing conditions over the North Atlantic in two fundamental ways: 1) by reducing the vertical wind shear across the tropical Atlantic and Caribbean Sea, and 2) by producing a structure and location of the African easterly jet which is thought to be more efficient for providing energy to developing tropical systems as they propagate westward from the African coast.

During active hurricane seasons, the continental United States usually experiences a higher number of landfalling hurricanes than average. The Caribbean region is also far more at risk of experiencing a tropical storm or hurricane during active seasons than at other times, as was recently observed during the 1995, 1996, and 1998 seasons. In an average season the United States experiences 1-2 land-falling hurricanes, while the Caribbean Islands experience 1 hurricane.

The hurricane season for the North Atlantic basin (which includes the North Atlantic Ocean, Caribbean Sea and Gulf of Mexico) officially runs from June 1st through November 30th. During this period the average number of systems reaching tropical storm status (maximum sustained winds between 39-73 mph), hurricane status (maximum sustained winds of at least 74 mph) and major hurricane status (maximum sustained winds exceeding 110 mph, and corresponding to categories 3-4-5 on the Saffir-Simpson scale ) are nine, six, and two, respectively. However, the vast majority of tropical storm and hurricane activity typically occurs during August - October, which is considered the peak of the hurricane season.

This outlook is meant to provide users with a consensus statement from NOAA scientists regarding the upcoming Atlantic basin hurricane activity based on current and expected climate conditions as described above. The expectation of above-average activity during 1999 is not based on global warming associated with elevated carbon dioxide levels.

This outlook is not designed to compete with other existing hurricane forecasts and outlooks issues by persons or groups outside of NOAA. We gratefully acknowledge the pioneering research provided by Dr. William Gray and others, which has significantly increased scientific understanding of the association between the various climate factors (particularly the ENSO cycle) and the atmospheric circulation features that affect Atlantic basin 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 tropical storm and hurricane activity.


1) Far more damage can be done by one major hurricane hitting a heavily populated area than by several major hurricanes hitting sparsely populated areas or, of course, not making landfall at all.

Because of this, hurricane-spawned disasters can occur even in relatively inactive years from landfalling systems.

2) Increased tropical storm and hurricane activity during a particular year does not automatically mean increased storm-related damage. For example, in 1992 Hurricane Andrew, the only major hurricane to develop in that relatively inactive year, caused over $25 billion in damage to the continental United States. In contrast there was less than $4 billion in damage to the continental United States during 1995, one of the most active seasons on record.

3) Although major hurricanes tend to be the deadliest and costliest tropical systems, disasters can and indeed do occur due to flooding from less intense hurricanes and tropical storms.

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Page last modified: May 27, 1999
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