The 2013 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). The eastern Pacific hurricane region covers the eastern North
Pacific Ocean east of 140°W north of the equator.
Interpretation of NOAA’s eastern Pacific hurricane season outlook
This outlook is general guide to the expected overall activity during 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 relatively quiet. It only takes one hurricane (or even a tropical storm) to cause a disaster.
Therefore, residents, businesses, and government agencies of coastal and near-coastal regions are urged to prepare for every hurricane season regardless of this, or
any other, seasonal outlook. NOAA, the Federal Emergency Management Agency (FEMA), the NHC, the Small Business Administration, and the American Red Cross all provide
important hurricane preparedness information on their web sites.
NOAA does not make seasonal hurricane landfall predictions
NOAA does not make seasonal hurricane landfall predictions. Hurricane landfalls are largely determined by the weather patterns in place as the hurricane approaches,
which are only predictable when the storm is within several days of making landfall.
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. The seasonal activity is expected to fall within
these ranges in 7 out of 10 seasons with similar climate conditions and uncertainties to those expected this year. They do not represent the total possible ranges of
activity seen in past similar years.
This outlook is based on predictions of large-scale climate factors and conditions known to strongly influence seasonal eastern Pacific hurricane activity, along with
climate model forecasts. The outlook also takes into account uncertainties inherent in such climate outlooks.
Sources of uncertainty in this seasonal outlook
- Predicting El Niño and La Niña (also called ENSO) impacts is an ongoing scientific challenge facing climate scientists today. Such forecasts made during the spring generally have limited skill.
- Many combinations of named storms and hurricanes can occur for the same general set of climate conditions. For example, 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.
2013 Eastern Pacific Hurricane Outlook Summary
NOAA’s 2013 eastern Pacific Hurricane Season Outlook indicates a 55% chance of a below-normal season, a 35% chance of a near-normal season,
and a 10% chance of an above normal season. See NOAA definitions of above, near-, and below- normal seasons. The eastern
Pacific hurricane region covers the eastern North Pacific Ocean east of 140oW north of the equator.
This outlook is based on the analysis and prediction of three climate signals:
Historically, these conditions tend to suppress eastern Pacific hurricane activity. We estimate a 70% chance of
occurrence for each of the following ranges of activity this season:
- 11-16 named storms,
- 5-8 hurricanes,
- 1-4 major hurricanes,
- An ACE range 60%-105% of the median.
The seasonal activity is expected to fall within these ranges in 7 out of 10 seasons with similar climate conditions
and uncertainties to those expected this year. They do not represent the total possible ranges of activity seen in past similar years.
Note that the predicted ranges are centered below the official NHC 1981-2010 seasonal averages of 15 named storms, 8
hurricanes, and 4 major hurricanes.
There will be no further updates to this outlook.
1. Expected 2013 Activity
This Outlook is a general guide to the expected overall activity for the 2013 eastern Pacific hurricane season. It is not a seasonal hurricane landfall forecast, and
it does not imply levels of activity for any particular location.
Known climate signals and evolving oceanic and atmospheric conditions, combined with dynamical model forecasts, indicate that a below-normal 2013 eastern Pacific
hurricane season is most likely. This outlook calls for a 55% chance of a below-normal season, a 35% chance of a near-normal season, and a 10% chance of an
An important measure of the total seasonal activity is NOAA’s Accumulated Cyclone Energy (ACE) index, which accounts
for the combined strength and duration of tropical storms and hurricanes during the season. We estimate a 70% chance that the 2013 seasonal ACE index will be in the
range of 60%-105% of the median. According to NOAA’s definitions of season strength, an ACE value below 80% of the 1981-2010
median indicates a below normal season, and a value of 80%-115% of the median indicates a near-normal season.
Consistent with the expected ACE range, other likely (70% chance) ranges of activity for 2013 are 11-16 named storms, 5-8 hurricanes, and
1-4 major hurricanes.
This outlook is consistent with climate model forecasts. Predictions from NOAA’s Climate Forecast System (CFS), the European Centre for Medium Range Weather
Forecasting (ECMWF), and the EUROpean Seasonal to Inter-annual Prediction (EUROSIP) ensemble are all suggesting below-normal or near-normal tropical cyclone
activity in the eastern Pacific this season, though their forecast skill for the region is limited at this lead time.
2. Science behind the outlook
This outlook is based on the analysis and prediction of three climate signals. The first is a continuation of conditions that have been
suppressing eastern Pacific hurricane activity since 1995. The second is a likely continuation of ENSO-neutral
conditions through the season. The third is an expectation for near- or below-average sea-surface temperatures in the Niño-3 region of
the eastern tropical Pacific Ocean. SSTs in this region are an additional predictor for eastern Pacific hurricane activity, especially in the presence of
a. Expected continuation of low-activity hurricane era in the eastern Pacific
East Pacific hurricane seasons have been less active since 1995, while the Atlantic Basin has experienced increased activity. During 1995-2012, 39% of eastern
Pacific hurricane seasons were below normal, 39% were near normal, and only 22% were above normal. Seasons during this period averaged about 13 named storms,
7 hurricanes, and 3 major hurricanes, with an ACE value of 88% of the median.
Associated with the climate conditions that have contributed to this reduction in eastern Pacific hurricane activity, the Pacific
Inter-Tropical Convergence Zone (ITCZ) has been shifted farther north, allowing for extensive southwesterly flow into the eastern tropical North Pacific. Also, the
upper-level ridge over Mexico has been stronger than average, resulting in enhanced upper-level easterly winds. This combination of factors leads to increased
vertical wind shear, which typically limits the number, intensity, and duration of tropical storms and hurricanes. Also, these storms tend to form closer to Mexico
and closer to cooler ocean temperatures, both of which limit their duration.
The levels of hurricane activity since 1995 in the eastern Pacific (and the Atlantic basin) contrast sharply with those of the preceding period 1982-1994. The eastern
Pacific was much more active during this earlier period, while the Atlantic basin was more suppressed. For the eastern Pacific, 62% of hurricane seasons during
1982-1994 were above normal, 23% were near normal, and only 15% were below normal. Seasons during this period averaged about 18 named storms, 10.5 hurricanes, and
5 major hurricanes, with an ACE value of 150% of the median. This average value falls within NOAA’s definition for an above-normal season.
b. ENSO-neutral conditions
The ENSO (El Niño/ Southern Oscillation) is an important climate predictor for eastern Pacific hurricane activity. The three phases of ENSO are El Niño, La Niña, and
Neutral. El Niño acts to reduce the vertical wind shear, and is therefore more conducive to eastern Pacific hurricane activity. Conversely, La Niña increases the
wind shear and usually suppresses the activity. These typical impacts can be strongly modulated by conditions associated with the tropical multi-decadal signal.
SSTs in the eastern equatorial Pacific (i.e. the Niño-3 region) are also used to predict seasonal eastern Pacific hurricane activity, especially in the presence of
ENSO-neutral conditions have been present since last summer. Currently, equatorial Pacific SSTs are near average and the Niño 3.4 index is
slightly below zero. The equatorial Pacific sub-surface temperatures and oceanic heat content are also near average.
Most models contained in the suite of IRI/ CPC Niño 3.4 SST forecasts predict ENSO-neutral conditions to continue through ASO, with the
statistical model forecasts being generally cooler than the dynamical model forecasts. The CFS T-382 high-resolution model predicts La Niña for
ASO, which is consistent with its forecast for increased vertical wind shear across the eastern tropical Pacific.
The observations, ENSO model forecasts, the official CPC/IRI ENSO forecast issued in early May, all suggest that
ENSO-Neutral conditions are likely to continue through the summer and fall (55% chance). El Niño is not expected to develop this summer and enhanced the seasonal
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