NOAA 2024 Atlantic Hurricane Season Outlook

The 2024 North Atlantic Hurricane Season Outlook is an official product of the National Oceanic and Atmospheric Administration (NOAA) Climate Prediction Center (CPC). The outlook is produced in collaboration with hurricane experts from NOAA’s National Hurricane Center (NHC) and Atlantic Oceanic and Meteorological Laboratory (AOML). The Atlantic hurricane region includes the North Atlantic Ocean, Caribbean Sea, and Gulf of Mexico.

Interpretation of NOAA's Atlantic hurricane season outlook:
This outlook is a general guide to the expected overall activity during the upcoming hurricane season. It is not a seasonal hurricane landfall forecast, and it does not predict levels of activity for any particular location.

Preparedness:
Hurricane-related disasters can occur during any season, regardless if the season is active or relatively quiet. It only takes one hurricane (or 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 Ready.gov and Listo.gov, the National Hurricane Center, 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, and those patterns 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 analyses of 1) predictions of large-scale climate factors known to influence seasonal hurricane activity, and 2) climate forecast models that directly predict seasonal hurricane activity. The outlook also takes into account uncertainties inherent in such climate outlooks.

Preparedness for tropical storm and hurricane landfalls:
It only takes one storm hitting an area to cause a disaster, regardless of the overall activity for the season. Therefore, residents, businesses, and government agencies of coastal and near-coastal regions are urged to prepare every hurricane season regardless of this, or any other, seasonal outlook.

Sources of uncertainty in the seasonal outlooks:

1. Predicting El Niño and La Niña events (also called the El Niño-Southern Oscillation, or ENSO) and their impacts on North Atlantic basin hurricane activity, is an ongoing scientific challenge facing scientists today. Such forecasts made during the spring generally have limited skill, but that skill increases during the summer. Specific to this outlook, the major sources of uncertainty are rooted in the interplay between the current El Niño and the conditions local to the North Atlantic.
2. 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 shorter-lived storms or fewer longer-lived storms with greater intensity.
3. Model predictions of various factors known to influence seasonal hurricane activity in the Atlantic region, such as sea surface temperatures (SSTs), vertical wind shear, moisture, and atmospheric stability are still showing some spread for August-October (ASO), the peak months of the hurricane season, and it is unclear as to exactly how conducive these conditions will be for tropical cyclone development.
4. Shorter-term weather patterns that are unpredictable on seasonal time scales can sometimes develop and last for weeks or months, possibly affecting seasonal hurricane activity.

a. Predicted Activity

NOAA's updated outlook for the 2024 Atlantic Hurricane Season indicates that an above-normal season is most likely, with low possibilities the season could be near-normal and even lower odds for a below-normal season. The outlook calls for an 85% chance of an above-normal season, along with a 10% chance for a near-normal season and a 5% chance for a below-normal season. See NOAA definitions of above-, near-, and below-normal seasons. The Atlantic hurricane region includes the North Atlantic Ocean, Caribbean Sea, and Gulf of Mexico.

The updated 2024 outlook calls for a 70% probability for each of the following ranges of activity during the 2024 hurricane season, which officially runs from June 1st through November 30th:

• 17-25 Named Storms
• 8-13 Hurricanes
• 4-7 Major Hurricanes
• Accumulated Cyclone Energy (ACE) range of 150%-245% of the median

The seasonal 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 ranges of activity seen in past similar years. These expected ranges are centered well above the 1991-2020 seasonal averages of 14 named storms, 7 hurricanes, and 3 major hurricanes. Most of the predicted activity is likely to occur during the peak months (August-October, ASO) of the hurricane season.

The North Atlantic hurricane season officially runs from June 1st through November 30th. This outlook will be updated in early August to coincide with the onset of the peak months of the season (ASO).

b. Reasoning behind the outlook

1. The set of conditions that have produced the ongoing high-activity era for Atlantic hurricanes which began in 1995 are likely to continue in 2024. These conditions include warmer sea-surface temperatures (SSTs) and weaker trade winds in the Atlantic hurricane Main Development Region (MDR), along with weaker vertical wind shear, and an enhanced West African monsoon. The oceanic component of these conditions is often referred to as the Atlantic Multidecadal Oscillation (AMO), while the ocean/atmosphere combined system is sometimes referred to as Atlantic Multidecadal Variability (AMV). The MDR spans the tropical North Atlantic Ocean and Caribbean Sea. Of note, the SSTs in the MDR are at record warm levels. Currently observed SSTs in the MDR and North Atlantic are similar to those normally observed in late July and early August. Saharan Air Layer outbreaks could mitigate some of the record warming that has been observed so far this year. Tradewinds are quite weak, and the circulation with the West African Monsoon is near average, though predicted to be above-average for the entire season.
2. 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 (77%), with a small probability for ENSO-neutral (22%), and a negligible chance of an El Niño event (1%). During a high-activity era, ENSO-neutral is typically associated with above-average levels of activity. La Niña tends to reinforce those high-activity era conditions and further increases the likelihood of an above-normal season.

DISCUSSION

NOAA's outlook for the 2024 Atlantic Hurricane Season indicates that an above-normal season is most likely (85% chance). The outlook also includes a 10% chance of a near-normal season, and a 5% chance of a below-normal season.

The 2024 North Atlantic hurricane season is predicted to produce (with 70% probability for each range) 17-25 named storms, of which 8-13 are expected to become hurricanes, and 4-7 of those are expected to become major hurricanes. These ranges are centered well above the 1991-2020 period averages of about 14 named storms, 7 hurricanes, and 3 major hurricanes. The 2024 forecast ACE range is centered above the threshold for a hyper-active season (165% of median).

The 2024 North Atlantic hurricane season could be the eighth out of the last 10 with above-average activity. Since the current Atlantic high-activity era began in 1995, 20 of 29 (about 70%) seasons have had above-normal activity, and only 5 (17%) and 4 (14%) have had near- and below-normal activity, respectively, based on the 1951-2020 climatology. Also, 9 (almost half) of the above-normal years (thus 31% of the 29 years) have been hyper-active (% median ACE ≥ 165%).

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 all named storms and hurricanes during the year. This 2024 outlook indicates a 70% chance that the seasonal ACE range will be 150-245% of the median. According to NOAA’s hurricane season classifications, an ACE value between 75.4% and 130% of the 1951-2020 median reflects a near-normal season. Values above (below) this range reflect an above- (below-) normal season. The 2024 predicted ACE range is centered in the above-normal range, and furthermore above the threshold for a hyper-active 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 not possible to reliably predict the number or intensity of landfalling hurricanes in a seasonal outlook, or whether a given locality will be impacted by a tropical storm or hurricane this season.

2. Science behind the Outlook

NOAA’s North Atlantic Hurricane Season Outlooks are based on predictions of the main climate factors and their associated conditions known to influence seasonal Atlantic hurricane activity. These predictions 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) HiFLOR-S and SPEAR-MED models, 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.

Two of the statistical tools and one of the hybrid tools were updated for this year. The multiple-linear regression tool was updated for new coefficients, and a redundant predictor (SST anomalies in the MDR versus local climatology) was removed as it was found to add no information over the SST anomalies in the MDR versus the global topics. The AOML regression tool was updated to add properly calibrated spread. The hybrid prediction method using the NMME was updated to incorporate the CESM1 constituent of the NMME.

NOAA's 2024 North Atlantic hurricane season outlook reflects the expectation of complementary climate factors during August-October (ASO), as follows:

1. The underlying climate factor again this season is the continuation of the high-activity era for Atlantic hurricanes, which began in 1995 in association with a transition to the warm phase of the Atlantic Multidecadal Oscillation (AMO). The recently observed and predicted atmospheric conditions for ASO 2024 reflect the warm AMV phase , and with several factors conducive for higher levels of activity such as weaker trade winds and warmer SSTs across much of the MDR, a more conducive African easterly jet, weaker vertical wind shear, and an above-average West African monsoon. When the oceanic and atmospheric conditions are considered as a whole, the variability is being more commonly referred to as Atlantic Multidecadal Variability (AMV) in recent literature. The SSTs in the MDR (North Atlantic) are at (near) record high levels. Tradewinds are weaker than average. Outflow from the West African Monsoon is not yet well established, but this is likely an impact of intraseasonal oscillations. Predictions of 200-850-hPa vertical wind shear are for very low levels, with some tools indicating values in the lower tercile of values relative to the 1991-2020 model history in absolute values, and lowest in the model record for total shear values.
2. The most recent NOAA ENSO probability forecast indicates a 77% chance that La Niña conditions will develop through the hurricane season, and a 22% chance that ENSO-neutral conditions could be in place during the peak months (ASO) of the season. The ENSO outlook calls for elevated odds of a moderate to strong La Niña this year, though uncertainty at these leads prevents us from deterministically delineating between a moderate or a strong La Niña. La Niña conditions were present during ASO of 2020, 2021, and 2022, with above-average activity during each of those years.

La Niña represents one phase of the climate phenomenon known as ENSO (El Niño-Southern Oscillation). The three phases of ENSO are El Niño, La Niña, and ENSO-neutral. El Niño tends to suppress Atlantic hurricane activity, while La Niña tends to enhance it. These impacts can be strongly modulated by conditions associated with a low- or high-activity era, and also by short-lived conditions during any specific year.

As of May 9, 2024, 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 a relatively high potential for 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 60% of the 26 models indicate La Niña conditions, with 2 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 below-normal vertical wind shear over the MDR. The shear predicted by the NMME this year is a record low for that modeling system. This is likely associated with the model predictions of La Niña, which is typically associated with below-normal vertical wind shear, especially over the western Atlantic basin.

The official NOAA ENSO outlook from May of 2024 indicates about a 77% chance of La Niña during the peak months (ASO) of the hurricane season, only a 22% chance of ENSO-neutral and a 1% chance of El Niño. Furthermore, the ENSO team also has indicated a 45% chance of a moderate to strong La Niña event (i.e. ASO Niño 3.4 SST anomaly of -1.0 °C or lower), though the increasing intensity of a La Niña event does not always translate into increasing impacts. These teleconnections typically decrease shear over the MDR, thus La Niña conditions do not inhibit tropical storm and hurricane formation in the Atlantic Basin.

Therefore, the current hurricane season outlook reflects the expectation that the La Niña conditions will complement and potentially reinforce the ongoing set of conditions associated with the current high-activity era for Atlantic hurricanes (discussed below).

b. Predicted conditions within the MDR

SSTs are currently above-average across the MDR, with an area-averaged anomaly during April of +1.22 °C (the value during 2023 was +0.46 °C). For the MDR as a whole, both the CFS and NMME models predict above-average SSTs during ASO, with the NMME predicting record warm values. The differences between MDR SSTs and the global tropics is another predictor favoring an above-normal season, and has been linked to some hyper-active years. Among the NMME models used in the hybrid outlook, the predicted values of MDR SST anomalies range from +0.55 °C to +1.05 °C, with the multi-model, spatial average being +0.86 °C. However, most models tend to have only modest skill in predicting the strength of the Atlantic SST anomalies this far in advance, though these model predictions are consistent with the ongoing warm phase of the AMV. SSTs across the North Atlantic basin are presently at or near record values and predicted to stay above-normal at least through ASO.

Two inter-related atmospheric features, also related to the warm phase of the AMO/AMV that are typically analyzed, are anomalous winds at mid-levels (850-hPa, 700-hPa, and 600-hPa) across the central and eastern tropical Atlantic and the strength of the West African monsoon system. The 850-hPa winds show westerly anomalies, indicative of weaker trade winds. The outflow at 200-hPa from the West African Monsoon, as analyzed by 200-hPa Velocity Potential Anomaly and divergent wind, is showing a normal circulation. That signal has varied significantly, though variance in that signal before the core of the West African Monsoon season is common. If the monsoon is enhanced, as indicated in many of the model outlooks, then that would also favor increased Atlantic hurricane activity. These interrelated features include: 1) anomalously warm SSTs and decreased vertical wind shear, 2) an African Easterly Jet structure that allows for increased rotation of low-pressure cloud systems (aka African easterly waves) moving westward from Africa, and 3) the combination of increased moisture and decreased atmospheric stability. Because of these conditions, African easterly waves can develop more easily into tropical storms and hurricanes.

c. Factors contributing to the uncertainty

The main uncertainty in this seasonal hurricane outlook is timing of the transition to La Niña and the potential delay in onset of the resultant teleconnections. The odds for the development of La Niña are currently at 77%, which is confident but not certain. Additionally, the teleconnections from La Niña are not instantaneously realized and can be delayed by intraseasonal oscillations. A secondary source of uncertainty is in the local conditions in the Atlantic Basin. The SSTs are at or near record values, but there exists uncertainty on if the SSTs will remain as anomalously warm or return closer to climatological values as the Saharan Air Layer impacts solar insolation. Most model forecasts and even simple extrapolation of climatological cycles result in extremely favorable conditions across the Atlantic Basin. The impact of the combination of these various climate factors should be much clearer by the time of the August update of this outlook.

NOAA FORECASTERS

• Matt 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

• Eric Blake, Senior Hurricane Specialist; Eric.S.Blake{at}noaa.gov
• Dr. Chris Landsea, Branch Chief; Chris.Landsea{at}noaa.gov
• Dr. Richard Pasch, Senior Hurricane Specialist; Richard.J.Pasch{at}noaa.gov

• Stanley Goldenberg, Meteorologist; Stanley.Goldenberg{at}noaa.gov
• Dr. Hosmay Lopez, Oceanographer; Hosmay.Lopez{at}noaa.gov

REFERENCES

• Bell, G. D., and M. Chelliah, 2006: Leading tropical modes associated with interannual and multi-decadal fluctuations in North Atlantic hurricane activity. J. Climate, 19, 590-612.

• Blake, E. S., P. Klotzbach, and G. D. Bell, 2018: Climate factors causing the extremely active 2017 Atlantic hurricane season. Presented at AMS 33rd Conference on Hurricanes and Tropical Meteorology, April 2018.

• Goldenberg, S. B., C. W. Landsea, A. M. Mestas-Nuñez, and W. M. Gray, 2001: The recent increase in Atlantic hurricane activity: Causes and implications. Science, 293, 474-479.

• Goldenberg, S. B. and L. J. Shapiro, 1996: Physical mechanisms for the association of El Niño and West African rainfall with Atlantic major hurricane activity. J. Climate, 9, 1169-1187.

• Gray, W. M., 1984: Atlantic seasonal hurricane frequency: Part I: El Niño and 30-mb quasi-bienniel oscillation influences. Mon. Wea. Rev., 112, 1649-1668.

• Klotzbach, P.J., and W. M. Gray, 2008: Multi-decadal Variability in North Atlantic Tropical Cyclone Activity. J. Climate, 21, 3929 - 3935.

• L’Heureux, M. L., and Coauthors, 2019: Strength Outlooks for the El NiñoSouthern Oscillation. Wea. Forecasting, 34, 165175, https://doi.org/10.1175/WAF-D-18-0126.1.

• West, R., Lopez, H., Lee, S. K., Mercer, A. E., Kim, D., Foltz, G. R., & Balaguru, K. (2022). Seasonality of interbasin SST contributions to Atlantic tropical cyclone activity. Geophysical Research Letters, 49(4), e2021GL096712.