There is a 45% probability of a below normal tropical eastern North Pacific hurricane season during 2004, a 45% probability of near-normal season, and only a 10% probability of an above-normal season, according to a consensus of scientists at the National Oceanic and Atmospheric Administration's (NOAA) Climate Prediction Center (CPC), the Hurricane Research Division (HRD) and the National Hurricane Center (NHC). See Background Information for NOAA's definitions of above-, near-, and below-normal seasons.

The 2004 tropical eastern North Pacific outlook calls for 13-15 tropical storms (average is 15 to 16), with 6-8 becoming hurricanes (average is 9), and 2-4 becoming major hurricanes (average is 4 to 5). This expected activity is based on an expected continuation of ENSO-neutral conditions through August, combined with the overall reduced hurricane activity observed since 1995.

This is the second year that NOAA has issued an experimental outlook for the eastern North Pacific hurricane region, which covers the eastern North Pacific east of 140oW. Official hurricane outlooks for this region are expected to begin with the 2005 season.

DISCUSSION

1. Expected Activity - 45% Chance Below Normal, 45% Chance Near Normal, 10% chance Above Normal

An important measure of the overall seasonal activity is NOAA’s Accumulated Cyclone Energy (ACE) index, which accounts for the collective strength and duration of tropical storms and hurricanes during a given hurricane season (see Background Information). The ACE index is also used to define the above-, near-, and below-normal seasons.

For the 2004 tropical eastern North Pacific hurricane season, the ACE index is expected to be 65%-95% of the median. The main climate signals for this prediction are the expected continuation of ENSO neutral conditions through August 2004, combined with the ongoing trend of reduced eastern North Pacific hurricane activity observed since 1995. This reduced activity has occurred coincident with generally above-normal Atlantic hurricane seasons observed since 1995.

The East Pacific hurricane season is expected to bring 13-15 tropical storms, with 6-8 becoming hurricanes, and 2-4 becoming major hurricanes {categories 3-4-5 on the Saffir-Simpson scale}. While it is reasonable to expect this range of tropical storms, hurricanes, and major hurricanes, the total seasonal activity measured by the ACE index can certainly be in the expected range without all three of these criteria being met.

Most tropical storms that form in the eastern North Pacific track westward into open waters, sometimes reaching Hawaii and beyond. An additional one to two tropical storms either head northward or recurve toward western Mexico, and influence the summer precipitation amounts there. Regardless of their track East Pacific tropical storms and hurricanes can supply much needed moisture to the arid southwestern United States.

CAUTIONARY NOTES

1) It is important to recognize that it is currently not possible to confidently predict at these extended ranges the number or intensity of land falling hurricanes, or whether a particular locality will be impacted by a hurricane this season. Therefore, residents and government agencies of coastal and near-coastal regions should always maintain hurricane preparedness efforts regardless of the overall seasonal outlook.

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. Therefore, hurricane-spawned disasters can occur even in years with near-normal or below-normal levels of activity.

NOAA FORECASTERS

NOAA's Climate Prediction Center
Dr. Muthuvel Chelliah, Physical Scientist, Muthuvel.Chelliah@noaa.gov
Dr. Gerald Bell, Meteorologist, Gerry.Bell@noaa.gov
Dr. Kingtse Mo, Physical Scientist, Kingtse.Mo@noaa.gov

NOAA's Hurricane Research Division
Dr. Christopher Landsea, Meteorologist, Chris.Landsea@noaa.gov

NOAA's National Hurricane Center
Eric Blake, Meteorologist, Eric.S.Blake@noaa.gov