The 2024 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 hurricane experts from the NOAA National Hurricane Center (NHC) and the Hurricane Research Division (HRD). 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 location.
Preparedness
Hurricane-related disasters can occur during any season, even for years with low overall activity. It only takes one hurricane (or even a tropical storm) to cause a disaster. It is crucial that residents, businesses, and government agencies of coastal and near-coastal regions prepare for every hurricane season regardless of this, or any other, seasonal outlook. The Federal Emergency Management Agency (FEMA) through www.ready.gov and www.listo.gov, 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 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 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 climate model forecasts, and on predictions of large-scale climate factors and conditions that are known to strongly influence seasonal eastern Pacific hurricane activity. The outlook also takes into account uncertainties inherent in such climate outlooks.
Sources of uncertainty in this seasonal outlook
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Predicting El Niño and La Niña events (also called El Niño-Southern Oscillation, ENSO) and specific impacts on eastern Pacific hurricane activity is an ongoing scientific challenge facing climate scientists today. Such forecasts made during the spring generally have more uncertainty than those made closer to the peak of hurricane season.
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Uncertainty as to whether the eastern Pacific has shifted to a persistent low-activity era, or that the recent quiescent period will be short lived and there will be a return to the high-activity era that lasted from 2014-2019.
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Predicting the combined impacts associated with the Pacific Decadal Oscillation (PDO), ENSO, and the Atlantic Multidecadal Oscillation (AMO) remains a challenge, especially when they have different temporal variability that sometimes results in competing influences.
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Many combinations of named storms, hurricanes, and major 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.
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Shorter-term weather patterns that are unpredictable on seasonal time scales can sometimes develop and last for weeks or months within a season, possibly affecting seasonal hurricane activity.
2024 Eastern Pacific Hurricane Outlook Summary
a. Predicted Activity
NOAA's 2024 eastern Pacific Hurricane Season outlook indicates a below-normal season is most likely (60% chance). There is a 30% chance of a near-normal season and only 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 140°W and north of the equator.
The 2024 outlook calls for a 70% probability for each of the following ranges of activity:
- 11-17 Named Storms
- 4-9 Hurricanes
- 1-4 Major Hurricanes
- Accumulated Cyclone Energy (ACE) range of 50%-110% of the median.
The activity is expected to fall within these ranges in 70% of seasons with similar climate conditions and uncertainties to those expected this year. These ranges do not represent the total possible activity seen in past similar years. The predicted ranges are centered below the 1991-2020 averages of 15 named storms, 8 hurricanes, and 4 major hurricanes.
The eastern Pacific hurricane season officially runs from May 15th through November 30th. The peak months of the season are July-September (JAS).
There will be no further updates to this outlook.
b. Reasoning behind the outlook
Two main climate factors are expected to contribute to an below-normal 2024 hurricane season across the eastern Pacific hurricane basins, as follows:
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The latest monthly sea-surface temperature (SST) anomalies reflect El Niño conditions, on the path to the predicted La Niña, and a negative PDO structure, while also showing the North Atlantic SSTs as above-normal for much of the basin. SST anomalies in the regions where many of the tropical storms and hurricanes form (110°W - 140°W) are near normal. The predicted SST anomaly patterns indicate near or below-average SSTs across the eastern Pacific hurricane region, though there is some evidence of influence from the negative PDO related circulation pushing cooler waters southward. The cooler waters are expected to occur mainly east of 120°W. SSTs across the Atlantic Main Development Region (MDR) are above normal, with near record warmth. Historically, this combination tends to be associated with below-normal hurricane activity in the eastern Pacific, as La Niña does tend to have a larger influence than either the Pacific Decadal Oscillation (PDO) or Atlantic conditions. La Niña conditions, concurrent with a negative PDO, are common and found to reinforce a negative PDO.
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The most recent forecast from the NOAA Climate Prediction Center indicates La Niña conditions are likely through the hurricane season. The ENSO influence on eastern Pacific hurricane activity is highly dependent upon the background SST patterns across the eastern Pacific hurricane region and the Atlantic MDR. The combination of La Niña and above-normal temperatures in the Atlantic MDR tends to favor decreased eastern Pacific hurricane activity, often resulting in a below-normal hurricane season.
DISCUSSION
1. Expected 2024 activity
NOAA’s 2024 eastern Pacific Hurricane Season Outlook indicates a below-normal season is most likely (60% chance). There is a 30% chance of a near-normal season and only a 10% chance of an above-normal season.
The 2024 eastern Pacific hurricane season is predicted to produce (with a 70% probability for each range) 11-17 named storms, of which 4-9 are expected to become hurricanes, and 1-4 of those are expected to become major hurricanes. These ranges are centered below the 1991-2020 seasonal averages of 15 named storms, 8 hurricanes, and 4 major hurricanes.
An important measure of the total seasonal activity is NOAA’s Accumulated Cyclone Energy (ACE) index , which accounts for the combined intensity and duration of named storms and hurricanes during the season. This 2024 outlook indicates a 70% chance that the ACE range will be 50%-110% of the median. An ACE value of 80%-120% of the median indicates a near-normal season. Values above this range reflect an above-normal season, and values below this range reflect a below-normal season.
Specific predictions of the location, number, timing, and intensity of hurricane landfalls are ultimately related to the daily weather patterns which determine storm genesis locations and steering patterns. These patterns are not predictable weeks or months in advance. As a result, it is currently not possible to reliably predict the number or intensity of landfalling hurricanes at these extended ranges, or whether a given locality will be impacted by a tropical storm or hurricane this season.
2. Science behind the Outlook
NOAA’s eastern Pacific Hurricane Season Outlook is based on predictions of the main climate factors and their associated relationships to the hurricane season, as well as direct output from numerical models. The outlook is based on extensive monitoring, analysis, research activities, a suite of statistical prediction tools, and dynamical models. The dynamical model predictions come from the NOAA Climate Forecast System (CFS), NOAA Geophysical Fluid Dynamics Lab (GFDL) HiFLOR and SPEAR-MED modes, the North American Multi-Model Ensemble (NMME), the United Kingdom Met Office (UKMET) GloSea6 model, and the European Centre for Medium-Range Weather Forecasting (ECMWF) Seas5 model. ENSO forecasts are also provided from the NMME dynamical models contained in the suite of Niño 3.4 SST forecasts, which is compiled by NOAA’s CPC.
NOAA's 2024 eastern Pacific hurricane season outlook reflects two main factors:
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The predicted SST anomaly patterns across the eastern Pacific hurricane region indicate near to below-average SSTs and above-average SSTs across the Atlantic MDR. In the region where most tropical cyclones form in the eastern Pacific, SSTs are currently near normal. For the Pacific, these conditions also project onto the negative phase of the Pacific Decadal Oscillation (PDO) and also onto the warm (positive) phase of the Atlantic Multidecadal Oscillation (AMO) and the Atlantic Meridional Mode (AMM). Historically, this combination of climate patterns tends to be associated with below-normal activity in the eastern Pacific hurricane region. The exact interplay and net result of the interbasin relationships is uncertain and still a focus of ongoing research, and that uncertainty is reflected in the relatively moderate probabilities in this outlook.
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The most recent forecast from the NOAA Climate Prediction Center indicates La Niña conditions are likely through the hurricane season. The odds are highest for La Niña (69%), with a smaller probability for ENSO-neutral (30%), and a negligible chance of an El Niño event (1%). Historically, La Niña events usually mean less tropical storm/hurricane activity for the East Pacific, and often for the Central Pacific. During low-activity eras in the East Pacific, typically associated with high activity eras in the Atlantic (which we are in now), La Niña conditions can produce about as many storms as El Niño.
The most recent forecast from the CPC favors El Niño (91% chance) conditions during JAS with negligible odds for the development of La Nina (~0%). Historically, El Niño events usually mean more activity for the East Pacific, and often for the Central Pacific. During high activity eras in the East Pacific, typically associated with low activity eras in the Atlantic - which we are not in now, ENSO-neutral can produce about as many storms as El Niño. The conclusion the team drew from that is that during uncertain eras, ENSO can have an outsized impact, but that other factors can increase the uncertainty.
a. La Niña favored
An El Niño advisory is in place and a La Niña watch has been issued. The weekly SSTs are currently slightly above average across much of the central and eastern equatorial Pacific and the SST index for the Nino3.4 region is +0.5 °C. The Niño 3.4 index has shown a significant cooling trend since December 2023 and the weekly Niño 3.4 index has decreased from +1.9 °C in December of 2023 to its current value of +0.5 °C. The wind and outgoing longwave radiation patterns over the central Pacific are also reflecting a breakdown of atmospheric response to last year’s El Niño forcings, and are currently showing more influence from intraseasonal modes.
Looking forward, model-predicted SST anomalies in the Niño 3.4 region generally indicate La Niña (Niño 3.4 index less than -0.5 °C) conditions throughout the hurricane season. The dynamical model average (dashed black line) indicates La Niña through the late summer and autumn of 2024, with only one modeling system indicating ENSO-neutral conditions, but still showing negative anomalies. When using a larger pool of models that includes multiple dynamical models, multiple statistical models, and unique combinations of those models, about 30% of the 26 models indicate La Niña conditions, with 4 results showing positive Niño 3.4 values.
NOAA’s Climate Forecast System (CFS) and the North American Multi-Model Ensemble (NMME) are predicting La Niña. The CFS and NMME predict above-normal shear over the East Pacific. The shear predicted by the NMME as used in the hybrid model is positive, indicating above-normal shear, whereas 2023 outlook was for below-normal shear.
b. Eastern North Pacific high- and low-activity eras
In addition to year-to-year fluctuations, eastern Pacific hurricane activity exhibits strong variability on decadal and multi-decadal time scales. Periods of decreased activity (such as 1971-1981 and 1995-2013) are called low-activity eras, and periods of increased activity (such as 1982-1994 and 2014-2019) are called high-activity eras, though it’s not clear if the lull in 2019 and 2020 were indeed an end to a high-activity era, or simply a pause, given that the 2023 season was above normal and 2022 was near the threshold for an above-normal season. These are different from the high- and low-activity eras in the Atlantic hurricane region. The differences in seasonal activity between these two eras for the eastern Pacific are considerable. High-activity eras average about 4.5 more named storms, 2.8 more hurricanes, 2.3 more major hurricanes, and 56% more ACE, than low-activity eras. During high-activity eras, above-normal seasons occur about three times more frequently (63% of seasons compared to 20%), and below-normal seasons are about four times less frequent (11% compared to 43%).
High- and low-activity eras in the eastern Pacific hurricane region are related to global patterns of SST anomalies that change slowly and last for many years. It is upon these patterns that the inter-annual ENSO signal overlays. One such pattern is called the Pacific Decadal Oscillation (PDO). The PDO spans most of the North Pacific Ocean, and is associated with decadal fluctuations in hurricane activity. The positive (negative) phase of the PDO tends to be associated with high- (low-) activity eras. Another SST pattern is the Atlantic Multi-decadal Oscillation (AMO), and when linked to wind patterns can be more broadly described as Atlantic Multidecadal Variability (AMV), measured through the Atlantic Meridional Mode (AMM). The cold (warm) phase of the AMO increases the likelihood of a high- (low-) activity era. The AMO helps to explain the inverse relationship in activity between the eastern Pacific and Atlantic basins, with a warm AMO/positive AMM favoring increased Atlantic activity and decreased eastern Pacific activity. The AMO is positive this year with warm SSTs in the North Atlantic.
The 1982-1994 high-activity era was associated with a cold AMO and a positive PDO, while the period from 2014-2020 exhibited higher activity and primarily featured a strong positive PDO, there is uncertainty about the classification of the activity regime in the Pacific. Such a short period of years would not define an activity era. The relative lull in activity during 2020 and 2021 could just be more consistent with repeat La Niña events overriding the multi-year signals, which could be the case in 2023. The intervening 1995-2013 low-activity era featured a warm AMO and negative PDO. Of the years when the August PDO was negative, approximately 70% of those years were near normal or below normal for activity (17 of 23 since 1971). The current value of the PDO is -1.03, and the SST patterns from this spring are similar to many low-activity years. The SST patterns in 2022 and 2023 were also similar, but the eastern Pacific experienced near-normal activity and above-normal activity, respectively, during those years. That variation shows that interannual variability can override the decadal signals.
There is high confidence that the current negative PDO pattern will persist through the hurricane season. One reason is that the current negative PDO signal partly reflects the synoptic-scale wind and pressure patterns during the past months, influenced by El Niño, which is forecast to completely fade. ENSO changes typically lead PDO changes by months to seasons, with studies showing ENSO leading the PDO by 6 to 24 months. In addition, JAS Niño 3.4 values and JAS PDO values are correlated at about 0.50, and the predictions for Niño 3.4 are well below zero (i.e., La Niña) in many models. The official ENSO outlook probabilities indicate the relatively high likelihood of La Niña during a low-activity era (right). During La Niña years in low-activity eras, tropical cyclone activity in the eastern Pacific exhibits a wide range of outcomes. The current outlook, to account for uncertainty in the activity era classification, includes a 10% chance for an above-normal season.
NOAA FORECASTERS
Climate Prediction Center
- Matthew Rosencrans, Physical Scientist, Matthew.Rosencrans{at}noaa.gov
- Dr. Hui Wang, Physical Scientist; Hui.Wang{at}noaa.gov
- Dr. Daniel Harnos, Meteorologist; Daniel.Harnos{at}noaa.gov
National Hurricane Center
- Eric Blake, Senior Hurricane Specialist; Eric.S.Blake{at}noaa.gov
- Dr. Christopher Landsea, Meteorologist; Chris.Landsea{at}noaa.gov
Hurricane Research Division
- Stanley Goldenberg, Meteorologist; Stanley.Goldenberg{at}noaa.gov
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