This 2019 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 specialists 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 location.
Hurricane-related 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. 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), 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 conditions and uncertainties to those expected this year. They do not represent the total possible range 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 which 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
1. 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.
2. 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.
3. Weather patterns that are unpredictable on seasonal time scales can sometimes develop and last for weeks or months, possibly affecting seasonal hurricane activity.
2019 Eastern Pacific Hurricane Outlook Summary
a. Predicted Activity
NOAA's 2019 eastern Pacific Hurricane Season Outlook indicates a 70% chance of an above-normal season. There is a 20% chance of a near-normal season and only a 10% chance of a below-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 north of the equator.
The 2019 outlook calls for a 70% probability for each of the following ranges of activity:
- 15-22 Named Storms
- 8-13 Hurricanes
- 4-8 Major Hurricanes
- Accumulated Cyclone Energy (ACE) range of 100%-180% 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. These predicted ranges are centered above the 1981-2010 averages of 15 named storms, 8 hurricanes, and 4 major hurricanes.
The eastern Pacific hurricane season officially runs from May 15th through November 30th.
There are no further updates to this outlook.
b. Reasoning behind the outlook
Two climate factors are expected to contribute to a stronger hurricane season across the eastern (and central) Pacific hurricane basin. These factors include El Niño, and above-average sea-surface temperatures (SSTs) across the eastern and central tropical North Pacific. These conditions are already in place, and are expected to continue through the peak months of the hurricane season (July-September, JAS).
The most recent forecast from the NOAA Climate Prediction Center indicates about a 60% chance of El Niño during JAS. The latest model forecasts predict a weak- or moderate-strength El Niño during this period, which means there is some uncertainty as to how much El Niño will enhance the hurricane season.
1. Expected 2019 activity
NOAA's 2019 eastern Pacific Hurricane Season outlook indicates a 70% chance of an above-normal season. There is a 20% chance of a near-normal season and only a 10% chance of a below-normal season. See NOAA definitions of above-, near-, and below-normal seasons.
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 2019 outlook indicates a 70% chance that the ACE range will be 100%-180% of the median. An ACE value of 80%-115% 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.
The 2019 eastern Pacific hurricane season is predicted to produce (with 70% probability for each range) 15-22 named storms, of which 8-13 are expected to become hurricanes, and 4-8 of those are expected to become major hurricanes. These ranges are centered well above the official NHC 1981-2010 seasonal averages of 15 named storms, 8 hurricanes, and 4 major hurricanes.
Predicting the location, number, timing, and strength of hurricane landfalls are ultimately related to the daily weather patterns, 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 hurricane this season.
2. Science behind the 2019 Outlook
NOAA's eastern Pacific hurricane season outlook is based on predictions of the main climate factors and their associated conditions known to influence the hurricane season. The outlooks are 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) models, the North American Multi-Model Ensemble (NMME), the United Kingdom Met Office (UKMET) GloSea5 model, and the European Centre for Medium Range Weather Forecasting (ECMWF) model. ENSO forecasts are also provided from a suite of statistical and other dynamical models contained in the suite of Niño 3.4 SST forecasts, which is compiled by the IRI (International Research Institute for Climate and Society) and the NOAA CPC.
NOAA's 2019 eastern Pacific hurricane season outlook reflects two main factors:
(1) The likely continuation of El Niño during the peak months of the hurricane season. El Niño generally enhances the eastern (and central Pacific) hurricane seasons, while La Niña usually suppresses them. El Niño enhances hurricane formation and intensification by decreasing the vertical wind shear.
(2) The likely continuation of above-average SSTs across much of the hurricane formation region northwestward across the subtropical eastern Pacific Ocean, in association with a positive phase of the Pacific Decadal Oscillation (PDO). SSTs have generally been well above average in this region since 2014, and models are predicting this warmth to continue through the hurricane season.
a. Weak or moderate-strength El Niño
El Niño developed in late 2018 and is still present. SSTs are currently 0.5°C to 1.5°C above average across the central and east-central equatorial Pacific, and the latest weekly SST index for the Niño 3.4 region is near 0.5°C. The Niño 3.4 region spans the east-central equatorial Pacific between 120°W-170°W and 5°N-5°S. El Niño is classified as a Niño 3.4 index at or above 0.5°C for five consecutive overlapping 3-month seasons, along with consistent atmospheric impacts. A weak El Niño is defined by a sustained Niño 3.4 index between 0.5°C and 1.0°C, and a moderate-strength El Niño is defined by a sustained Niño 3.4 index between 1.0°C and 1.5°C.
The current atmospheric anomalies reflect a weak El Niño. At present, its main convective forcing onto the atmosphere is confined to the western and central equatorial Pacific, as measured by Outgoing Longwave Radiation (OLR). In the tropics, low OLR values indicate high and cold cloud tops associated with deep convection, while high OLR values indicate little or no convection. The current El Niño is associated with negative OLR anomalies (enhanced convection) across the west-central and central equatorial Pacific and with positive OLR anomalies (suppressed convection) over Indonesia. A time-longitude section shows that this pattern has been very persistent since last winter. By comparison, a stronger El Niño would typically have a much farther eastward extension of enhanced convection than is currently observed.
The low-level (850-hPa) atmospheric zonal wind anomalies are also typical of a weak El Niño. In recent months, the low level easterly winds have been weaker than average (indicated by westerly anomalies, orange-red shading) mainly over the west-central or western equatorial Pacific Ocean. These conditions have been associated with the enhanced convection near the date line. A stronger El Niño would typically feature a farther eastward extension of the westerly anomalies.
Based on current conditions, the recent oceanic evolution, and the spread in model forecasts, NOAA's latest ENSO outlook indicates about a 60% chance of El Niño during JAS 2019.
Model predicted SST anomalies in the Niño 3.4 region for JAS 2019 generally reflect a weak or moderate-strength El Niño. Both the dynamical model average (red line) and statistical model average (green line) indicate a weak El Niño through the peak months of the hurricane season (JAS time period).
b. Eastern North Pacific SST anomalies
Eastern Pacific hurricane activity is also related to global patterns of SST anomalies that occur on decadal and multi-decadal time scales. One such pattern is called the Pacific Decadal Oscillation (PDO), and spans most of the North Pacific Ocean. This climate pattern is associated with decadal fluctuations in hurricane activity. It contributes to the background climate patterns upon which the inter-annual ENSO signals overlay.
Four of the last five eastern Pacific hurricane seasons were above normal, and were associated with above-average SSTs across the central and eastern Pacific hurricane regions. A similar period of increased activity and anomalous warmth was observed during 1981-1994. In both periods, the anomalously warm SSTs were associated with the positive phase of the PDO. In contrast, the intervening low-activity era of 1995-2013 was associated with below-average SSTs across the hurricane region and with a negative phase of the PDO.
The most recent SST anomaly pattern again shows above-average SSTs in the eastern and central Pacific hurricane regions, along with a larger-scale pattern that reflects the positive phase of the PDO.
For July-September 2019, NOAA's CFS model predicts a likely continuation of the anomalous warmth across a large portion of the tropical eastern and central North Pacific. This forecast is consistent with predictions from the NMME model and the GFDL models. Consequently, this 2019 hurricane outlook also reflects a prediction for above-average SSTs in the eastern Pacific main hurricane development region, along with a continued positive phase of the PDO. These conditions, combined with El Niño, suggest a high likelihood (70% chance) of another above-normal season in the eastern Pacific basin for 2019.
Climate Prediction Center
National Hurricane Center