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The eastern Pacific hurricane season outlook is an official product of the National Oceanic and Atmospheric Administration (NOAA) Climate Prediction Center (CPC), and is produced in collaboration with scientists from the NOAA National Hurricane Center (NHC).
Interpretation of NOAA’s eastern Pacific seasonal hurricane outlook
1. Preparedness
- This outlook provides the public with a general guide to the expected overall activity for the upcoming hurricane season. It is not a seasonal hurricane landfall forecast, and it does not imply levels of activity for any particular region.
- Hurricane disasters can occur whether the season is active or quiet. Residents, businesses, and government agencies of coastal and near-coastal regions should prepare for every hurricane season regardless of the seasonal outlook. NOAA, FEMA, the NHC, Small Business Administration, and the Red Cross all provide important hurricane preparedness information on their web sites. It only takes one hurricane (or even tropical storm) to cause a disaster.
2. NOAA does NOT make seasonal hurricane landfall predictions
- NOAA does not make hurricane landfall predictions on a seasonal timescale. Hurricane landfalls are largely determined by the weather patterns in place as the hurricane approaches, which are not predictable more than 5-7 days in advance.
3. Nature of this Outlook and the “likely” ranges of activity
- This outlook is probabilistic, meaning the stated “likely” ranges of activity have a certain likelihood of occurring. These ranges are typically seen in 2 of 3 seasons with similar climate conditions and uncertainties to those expected this year.
- These likely ranges do not represent the total ranges of activity seen in past seasons having similar climate conditions to those expected this year, but are simply the most likely.
- The outlook is based on predictions of large-scale climate factors known to be strong indicators of upcoming seasonal eastern Pacific hurricane activity, and takes into account uncertainties inherent in such climate outlooks (see item 4 below)
4. Three major sources of uncertainty in the seasonal outlooks
- El Niño and La Niña forecasts are presently the biggest source of uncertainty for the hurricane outlook. The period between March - July is referred to as the “springtime forecast barrier,” a period when predicting these phenomena can be difficult because the atmosphere is in a state of transition.
- Many combinations of named storms and hurricanes can occur for the same set of climate conditions. One cannot know with certainty whether a given climate signal will be associated with several short-lived storms or fewer longer-lived storms with greater intensity.
- Weather patterns that are unpredictable on seasonal time scales can sometimes develop and last for weeks or months, possibly affecting seasonal hurricane activity.
2009 Eastern Pacific Hurricane Outlook Summary
The Climate Prediction Center’s 2009 Eastern Pacific Hurricane Season Outlook calls for an 80% chance of a near- to below-normal season. Because of uncertainties in current predictions for El Nino, a near-normal and below-normal season are equally likely at this time. The outlook also indicates a 20% chance of an above-normal season. See NOAA definitions of above, near-, and below-normal seasons.
This outlook is based on the analysis and prediction of two main climate signals:
- The ongoing conditions that have been suppressing eastern Pacific hurricane seasons since 1995, and
- Either ENSO-neutral conditions or El Niño.
Climate patterns similar to those expected this year have historically produced a wide range of activity. Allowing for uncertainties, we estimate a 70% chance of occurrence for each of the following ranges of activity:
- 13- 18 named storms,
- 6- 10 hurricanes,
- 2- 5 major hurricanes,
- An ACE range of 70%-130% of the median
These likely ranges have been observed in about 70% of past seasons having similar climate conditions to those expected this year. They do not represent the total ranges of activity seen in those past seasons.
The eastern Pacific hurricane region covers the eastern Pacific Ocean east of 140oW north of the equator.
There will be no further updates to this outlook.
DISCUSSION
1. Expected 2009 Activity
This Outlook is a general guide to the expected overall activity for the 2009 eastern Pacific hurricane season. It is not a seasonal hurricane landfall forecast, and it does not imply levels of activity for any particular area.
The climate factors expected to guide the 2009 hurricane season are 1) the continuation of conditions that have been suppressing activity since 1995, and 2) either ENSO-neutral (no El Niño or La Niña) conditions or El Niño during the peak (July-September) of the season.
Historically, seasons with climate patterns similar to those expected this year have produced a wide range of activity. This outlook considers the historical distribution of activity for these climate factors, uncertainties in whether El Niño will develop, and the possibility of other unpredictable factors also influencing the season. Based on these factors, we estimate an 80% chance of a near-normal to below-normal hurricane season (40% chance of each), and a 20% chance of an above-normal season.
An important measure of total seasonal activity is NOAA’s Accumulated Cyclone Energy (ACE) index, which accounts for the collective strength and duration of tropical storms and hurricanes during the season. The ACE index is also used to define the season type. A value of 92%-138% of the median (Median value is 109) defines a near-normal season.
Based on the above factors, we estimate a 70% chance that the 2009 seasonal ACE range will be 70%-130% of the median. This range can be satisfied even if the numbers of named storms, hurricanes, or major hurricanes fall outside their likely ranges.
The likely (70% chance) ranges of activity for 2009 are: 13-18 named storms, 6-10 hurricanes, and 2-5 major hurricanes.
2. The ongoing low-activity hurricane era in the eastern Pacific
The eastern Pacific has seen generally suppressed hurricane activity since 1995. During 1995-2008, 64% of seasons were below normal, 29% were near normal, only one was above normal. These seasons averaged about 14 named storms, 7 hurricanes, and 3 major hurricanes, with an ACE value of 80% of the median. This value falls within NOAA’s definition for a below-normal season. During this low-activity era, only the strong El Niño of 1997 produced an above-normal season. This ongoing low-activity era is the main reason we expect the 2009 hurricane season to be near- or below- normal.
These conditions contrast with the previous high-activity era (1982-1994) in the eastern Pacific, in which 62% of hurricane seasons were above normal, 31% were near normal, and only one was below normal. These seasons averaged 18.2 named storms, 10.8 hurricanes, and 5.6 major hurricanes, with an ACE value of 157% of the median. This value falls within NOAA’s definition for an above-normal season. During this period, 5 of 8 El Niño episodes led to an above-normal season, and only 1988 was categorized as below-normal, due to a strong La Niña.
3. ENSO
The El Niño/ Southern Oscillation (ENSO) is an important climate predictor for eastern Pacific hurricane activity. El Niño generally produces conditions that are more conducive to hurricane activity, while La Niña suppresses the activity. However, these typical impacts can be strongly modulated by conditions associated with a low- or high-activity era.
La Niña dissipated during April 2009, and current sea-surface temperature anomalies in the east-central equatorial Pacific are near average. NOAA defines these conditions as ENSO-neutral.
There is considerable spread and uncertainty in the climate models regarding the evolution of ENSO during the next several months, and most of the models have historically shown little-to-no skill at this time of the year. The most recent dynamical model forecasts suggest El Niño will develop during the summer, although there is considerable disagreement as to its strength. In contrast, all of the recent statistical model forecasts suggest ENSO-neutral conditions will prevail.
The seasonal hurricane outlook reflects the possibility of El Niño developing and becoming strong enough to impact the season. However, because of the ongoing low-activity era, the historical data suggests these impacts would most likely raise the activity into the near-normal range. However, some dynamical model simulations predict significant El Niño-related circulation anomalies to develop this summer, would leaves open the possibility (20% chance) of an above-normal season. A below-normal season is more likely if ENSO-neutral conditions persist, and a near-normal season is more likely if El Niño develops.
NOAA FORECASTERS
Climate Prediction Center
Dr. Gerald Bell, Meteorologist, Gerry.Bell@noaa.gov
Dr. Jae Schemm, Meteorologist, Jae.Schemm@noaa.gov
National Hurricane Center
Eric Blake, Hurricane Specialist, Eric.S.Blake@noaa.gov
Todd Kimberlain, Hurricane Specialist, Todd.Kimberlain@noaa.gov
Dr. Christopher Landsea, Meteorologist, Chris.Landsea@noaa.gov
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www.nws.noaa.gov 
