NOAA 2023 Atlantic Hurricane Season Outlook

The updated 2023 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 2023 Atlantic Hurricane Season indicates that an above-normal season is most likely, with lower odds for a near- or below-normal season. The outlook calls for a 60% chance of an above-normal season, along with a 25% chance for a near-normal season and a 15% 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 2023 outlook calls for a 70% probability for each of the following ranges of activity during the 2023 hurricane season, which officially runs from June 1st through November 30th:

• 14-21 Named Storms, which includes the 5 named storms recorded thus far in 2023.
• 6-11 Hurricanes, which includes the 1 hurricane recorded thus far in 2023.
• 2-5 Major Hurricanes
• Accumulated Cyclone Energy (ACE) range of 105%-200% of the median, which includes the ACE from the 5 named storms (1 of which reached hurricane strength) recorded thus far in 2023.

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 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.

Compared to the May outlook (12-17 named storms, 5-9 hurricanes, and 1-4 major hurricanes), the August update has shifted all of the likely ranges of overall activity to higher levels. Also, there is an increase in the probability of above-normal activity (increased to 60% from 30%), and a decrease in the probabilities for a near-normal season (decreased to 25% from 40%) and a below-normal season (decreased to 15% from 30%). The predicted ACE range has also been shifted higher (up to 105%-200% from 70%-145%) since major hurricanes contribute significantly to the ACE. All of the ranges widened, except for major hurricanes due to uncertainties related to the competing impacts of ENSO versus the various factors in the Atlantic MDR such as record warm observed Atlantic SSTs.

b. Reasoning behind the outlook

This updated 2023 seasonal hurricane outlook reflects the expectation of competing and non-reinforcing large-scale climate factors during ASO, and this combination of factors have been historically associated with Atlantic hurricane seasons with a wide range of activity. Wide ranges in historical activity for similar climate conditions lead to increased uncertainty in the outlooks. The main climate factors for this outlook are:

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 2023. These conditions linked to the high-activity era typically include warmer SSTs, weaker trade winds, and with weaker 200-850 hPa vertical wind shear in the Atlantic hurricane Main Development Region (MDR), along with 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) ​​or the Tropical Multidecadal Mode (TMM). The MDR spans the tropical North Atlantic Ocean and Caribbean Sea (Goldenberg and Shapiro 1996). However, these atmospheric conditions are not as prominent or amplified at this point in the year as they were in the past 3 seasons (2020, 2021, and 2022). SSTs in the MDR are much warmer than last year, but the trade wind response has been more variable this year. The West African Monsoon rains have been above-normal through June 2023, but the associated lower-level and upper-level wind patterns have been closer to normal.
2. The most recent forecast from the NOAA Climate Prediction Center indicates El Niño conditions are expected through the hurricane season. The odds are highest for El Niño (96%), with low probabilities for ENSO-neutral (4%), and a negligible chance of a La Niña event (~0%). 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 with activity near the upper ends of the predicted ranges. Moderate or strong El Niño events typically have a dampening impact on tropical cyclone activity in the Atlantic basin by increasing 200-850 hPa vertical wind shear mainly in the western portion of the MDR.

DISCUSSION

NOAA's updated outlook for the 2023 Atlantic Hurricane Season indicates that an above-normal season is most likely (60% chance). The outlook also includes a 25% chance of a near-normal season, and a 15% chance of a below-normal season.

The 2023 North Atlantic hurricane season is predicted to produce (with 70% probability for each range) 14-21 named storms, of which 6-11 are expected to become hurricanes, and 2-5 of those are expected to become major hurricanes. These ranges are centered above the 1991-2020 period averages of about 14 named storms, 7 hurricanes, and 3 major hurricanes.

The 2023 North Atlantic hurricane season could mark a return to above-normal activity following a near-normal 2022 season. The last consecutive near-normal seasons were 2006 and 2007. Since the current Atlantic high-activity era began in 1995, 19 of 28 (about 68%) seasons have had above-normal activity, and only 5 (18%) and 4 (15%) have had near- and below-normal activity, respectively, based on the 1951-2020 climatology. Also, 9 (almost half) of the above-normal years (thus 32% of the 28 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 2023 outlook indicates a 70% chance that the seasonal ACE range will be 105-200% 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 2023 predicted ACE range is centered in the above-normal range, with a small overlap into the near-normal range, hence the reduced probabilities for a near- or below-normal season. The upper end of the ACE range is above the hyper-active threshold, and if the current El Niño event does not have a strong suppressing influence on Atlantic basin hurricane activity, the overall activity for 2023 could be above that threshold.

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. Newly added this year was a regression model designed to capture the combined variability based on the SSTs in both the Niño 3.4 region and the MDR simultaneously based on work at NOAA’s AOML (West et al. 2022).

NOAA's 2023 North Atlantic hurricane season outlook reflects the expectation of competing climate factors during August-October (ASO), as follows:

1. The main climate factor that could act to suppress Atlantic hurricane activity is the current El Niño event. The most recent NOAA ENSO probability forecast indicates a 96% chance that El Niño conditions will continue through the hurricane season, and only a 4% chance that ENSO-neutral conditions could be in place during the peak months (ASO) of the season. Additionally, the ENSO outlook calls for elevated odds of a moderate to strong El Niño this year. Strong El Niño conditions were last present in 2015 during ASO, and that year had below-normal activity.
2. One of the climate factors that would support above-normal activity is the expected 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) (Goldenberg et al. 2001, Bell and Chelliah 2006, Klotzbach and Gray 2008). 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 recently observed and predicted atmospheric conditions for ASO 2023 generally reflect the warm AMV phase, and with several factors conducive for higher levels of activity such as weaker trade winds, warmer SSTs across much of the MDR, and weaker 200-850 hPa vertical wind shear across much of the MDR. SSTs in the Atlantic MDR established a new record for warmth in June-July. The trade winds over the Atlantic were below average for most of June but near average for most of July. Also, the observations and predictions of the Atlantic MDR trade winds are not as anomalous as in the prior three years (2020, 2021, and 2022). Predictions of wind shear during 2020-2022 were for almost record low wind shear, while this year, the latest predictions are for below normal, but not record low, 200-850 hPa vertical wind shear.
3. The West African Monsoon, which is positively correlated with Atlantic tropical cyclone activity, is providing mixed signals. Typically the conditions associated with a warm AMV are coincident with an enhanced West African monsoon circulation, but in 2023, although the monsoon rains are above normal, the wind pattern is near-normal. The precipitation during June was well above normal, but West African Monsoon circulation values are not as anomalous as in the prior three years (2020, 2021, and 2022). Upper-level circulation over the West African Monsoon is near normal, and has been varying from unfavorable to favorable on intraseasonal time scales.
4. Enhanced June-July activity in the tropical Atlantic reinforces the expectation for an above-normal season. There have already been a total of five named storms in the North Atlantic hurricane basin; one subtropical storm in January, three tropical storms in June, and one hurricane in July for a sum total of 16.2 of ACE (16.7 % of median). Two of these (Tropical Storms Bret and Cindy) formed in the tropical Atlantic. In general, the activity prior to the peak months of ASO bears little relationship to the peak (ASO) and overall seasonal activity as there have been numerous years with even several pre-ASO named storms that produced near- and even below-normal overall activity. For instance, 1997 had six pre-ASO named storms, two of them reaching hurricane strength, but a strong El Niño event that year resulted in ASO activity that was far below normal with only 44.6% median ACE for the year, the second to lowest ACE in the current high-activity era. In addition none of those pre-ASO storms in 1997 formed in the MDR. If only the years with named storms developing pre-ASO in the tropics, specifically the southeast portion of Atlantic hurricane basin (~ 9-22°N, 15-77°W) are taken into account, that activity has been shown to be highly correlated with ASO and overall-seasonal activity since the early formation in the eastern MDR is an indicator that, when the peak months come, the MDR will be conducive to more development. In the current high-activity era, which began in 1995, of the 11 years with at least one named storm developing pre-ASO in that eastern MDR region, all but one (2013) have had above-normal overall activity and 7 of those years (64%) have had hyper-active levels of activity (i.e., % median ACE ≥ 165%). Almost half of the years since 1995 with above-normal activity and even several with hyper-active levels of activity did not have a pre-ASO storm develop in the eastern MDR. So although this pre-ASO tropical development is usually a sufficient condition for above-normal activity, it is by no means a necessary condition. This outlook includes the formation of tropical storms Bret and Cindy in the eastern MDR as one of several indicators strongly suggesting a season with above-normal or even hyper-active levels of activity. But the uncertainty due to the ongoing El Niño is still an issue even when considering the strong indicator related to these two storms.

El Niño 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 (Gray 1984; Goldenberg and Shapiro 1996). 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 July 13, 2023, El Niño conditions are present. The weekly SSTs are currently well above average across much of the central and eastern equatorial Pacific and the SST index for the Niño 3.4 region is +1.1°C. The Niño 3.4 index has shown a significant warming trend since December 2022 and the weekly Niño 3.4 index has increased from -0.5°C in February of 2023 to its current value of +1.1°C. The wind and outgoing longwave radiation patterns over the central Pacific are beginning to reflect El Niño conditions, but there are some portions of the anomaly patterns that are not yet aligned. The area of enhanced easterly anomalies over the eastern equatorial Pacific and the lack of upper-level anticyclones over the Central Pacific highlight the delayed atmospheric response. The OLR field, showing enhanced convection spreading over the Central and Eastern Pacific, is indicative of a growing atmospheric response.

Looking forward, model-predicted SST anomalies in the Niño 3.4 region generally indicate El Niño conditions (Niño 3.4 index greater than +0.5 °C) throughout the remainder of the North Atlantic hurricane season. The dynamical model average (dashed black line) indicates El Niño conditions continuing through the remainder of 2023. When using a larger pool of models that includes multiple dynamical models, many statistical models, and unique combinations of those models, 23 of 24 models indicate El Niño conditions at least through November 2023.

NOAA’s Climate Forecast System (CFS) and the North American Multi-model Ensemble (NMME) are also predicting that the current El Niño will persist throughout the remainder of the hurricane season. The CFS and the NMME predict below-normal shear over the MDR. The vertical wind shear predicted by the NMME this year is closer to climatology than the lower shear that was predicted last year for much of the Atlantic basin. The predicted shear for 2023 is closer to normal despite local factors favoring lower shear (e.g., warm AMO), and this could possibly be showing the influence of El Niño on the MDR vertical shear in the model outlooks. The pattern in the vertical wind shear is not typical of El Niño events of the past, so the uncertainty in the response contributes to the wide ranges in the outlook. . How this pattern will actually evolve, especially during the peak months of the season (ASO) is what will determine the overall seasonal hurricane activity.

The official NOAA ENSO outlook from July of 2023 indicates about a 96% chance of El Niño during the peak months (ASO) of the hurricane season, only small chances of ENSO-neutral (4%) or of La Niña (0%). Furthermore, the CPC ENSO team has also indicated a 76% chance of the current El Niño event becoming moderate or even strong (i.e. ASO Niño 3.4 SST anomaly of +1.0 °C or more), making the likelihood of teleconnections to the Atlantic more likely if we reach those higher Niño 3.4 values (L’Heureux, 2019). These teleconnections typically increase vertical shear over the MDR thus reducing Atlantic basin hurricane activity. These conditions that are not conducive to tropical cyclone formations may emerge later in the ASO period.

Therefore, the lower end of the ranges for the current hurricane season outlook reflects the possibility that the El Niño conditions could compete with, and thus interfere with, the ongoing set of conditions associated with the current high-activity era for Atlantic hurricanes (discussed below). The unknown extent of this potential interference is the main factor contributing to a heightened uncertainty in the outlooks.

b. Predicted conditions within the MDR

SSTs are currently well above-average across nearly all of the MDR, with an area-averaged anomaly during June-July of +1.23°C, compared to only +0.14°C during June-July of last year. The record warm SSTs could compete and mitigate the potential impacts of the ongoing El Niño. For the MDR as a whole, both the CFS and NMME models predict above-average SSTs during ASO. The positive difference between MDR SSTs and the global tropics is another predictor favoring an above-normal season, and has been linked to some hyper-active years (Blake et al. 2018).

Two inter-related atmospheric features, also related to the warm phase of the AMO/AMV that are typically analyzed, are anomalous low-level winds across the central and eastern tropical Atlantic and the strength of the West African monsoon system. The 700-hPa winds show a weak anticyclonic circulation along 20°N near the Cape Verde Islands. Across the rest of the MDR, anomalies are quite weak as the African Easterly Jet (AEJ) is near its climatological location and strength. Sahel precipitation resulting from the monsoonal circulations has been above normal despite the circulation pattern showing mid and upper-level winds as near normal. Trade winds are now near normal after being quite weak during June, though westerly anomalies are building northward across the MDR as of late July. Weaker trade winds generally contribute to heightened activity.

The outflow at the top of the West African Monsoon, as analyzed by 200-hPa Velocity Potential Anomaly and divergent wind, is showing a weaker than normal circulation, but the Sahel precipitation resulting from the monsoonal circulations has been above normal. The Madden-Julian Oscillation (MJO) and some other modes of variability may have played a role in some early suppression of upper-level divergence. Some analyses point to low frequency modes (ENSO) as the associated factor, so that may signal the beginnings of the first remote influences of the ongoing El Niño event. However, in general, the various factors conducive for development do not fully align until sometime in August, the first month of the peak months (ASO).

Overall, the conditions local to the Atlantic MDR are either near normal or conducive for tropical cyclone development. These inter-related conditions include 1) anomalously warm SSTs and decreased vertical wind shear in the MDR, 2) an African Easterly Jet structure closer to climatological position and amplitude the allows for some low-pressure cloud systems (i.e., African easterly waves) to develop, and 3) the combination of increased moisture and decreased atmospheric stability. Because of these conditions, the enhanced African easterly waves can potentially develop more easily into tropical storms and hurricanes, thus creating a forcing that would be in opposition to the forcing associated with El Niño

c. Factors increasing the uncertainty

The main uncertainty in this seasonal hurricane outlook is the interplay between the ongoing El Niño event which can lead to lower overall activity and the predicted set of conditions in the MDR that are conducive for more activity. Will the current El Niño event be strong enough to create a suppressing influence on North Atlantic basin hurricane activity, especially in the Main Development Region (MDR)? Will that influence counter the factors (e.g., above-normal MDR sea surface temperatures (SSTs), below-average vertical wind shear, etc.) that are conducive for more hurricane activity? If the influence from the El Niño event is strong enough, the season’s activity could be at the lower end of (or even below) the ranges predicted in this outlook. However, if the El Niño influence is minimal, the season’s activity could be at (or even above) the upper ranges predicted in this outlook.

Even though El Niño conditions will potentially create the traditional teleconnection patterns associated with lower tropical storm and hurricane activity in the Atlantic Basin, development could come later in the ASO period, and therefore the local (MDR) conditions could dominate during the beginning of the peak months allowing for robust activity during that period. The upward shift in all of the ranges of activity in this updated outlook compared to those in our May outlook reflects that we are more confident that local conditions will likely counterbalance the remote influences from El Niño for enough of ASO to allow for more activity during that period. An additional factor in the uncertainty is that SSTs in the MDR are record-setting, therefore analogs to past years are minimal. For years with similar activity to the midpoints of the outlook ranges, the global SST patterns were dramatically different, suggesting there are differences in the overlying atmospheric circulation patterns.

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.