There is a 50% probability of a below normal Northeast Pacific hurricane season during 2003, a 40% probability of near-normal season, and 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.

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

The 2003 Northeast Pacific outlook calls for 11-15 tropical storms (normal is 15), with 6-10 becoming hurricanes (normal is 9), and 2-5 becoming major hurricanes (normal is 4 to 5). This expected activity is based on a 70% likelihood that La Niña conditions will develop during the next few months, combined with the overall reduced hurricane activity observed since 1995.

DISCUSSION

1. Expected Activity - 50% Chance Below Normal, 40% 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 2003 East Pacific hurricane season, the ACE index is expected to be 60%-110% of the median. The main climate signal for this prediction is the likely development of La Niña conditions during the summer months. The increased vertical wind shear associated with La Niña is not conducive to an above-normal season. Historically, La Niña has been associated equally with near-normal and below-normal hurricane seasons, but rarely with an above-normal season.

Based on the historical record these conditions will likely bring 11-15 tropical storms, with 6-10 becoming hurricanes, and 2-5 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 East 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. 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 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

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