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NOAA 2021 Atlantic Hurricane Season Outlook

Issued: 4 Aug 2021

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Atlantic Hurricane Outlook & Seasonal Climate Summary Archive

The 2021 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 the National Hurricane Center (NHC) and the Hurricane Research Division (HRD). 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.


Hurricane-related disasters can occur whether 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), the National Hurricane Center (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, 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 1) predictions of large-scale climate factors known to influence seasonal hurricane activity, and 2) climate forecast models that directly predict seasonal hurricane activity.

Sources of uncertainty in the seasonal outlooks:

  1. Will La Niña develop and reinforce the conditions that are conducive for tropical cyclone development across the Atlantic Main Development Region (MDR)? Predicting El Niño and La Niña events (also called the El Niño-Southern Oscillation, or ENSO) and their impacts on Atlantic region hurricane activity, is an ongoing scientific challenge facing scientists today. Such forecasts made during the spring generally have limited skill, especially when border-line El Niño or La Niña events are predicted.

  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 shorter-lived storms or fewer longer-lived storms with greater intensity.

  3. Model predictions of various factors know 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.

2021 Atlantic Hurricane Season Outlook: Summary

a. Predicted Activity

NOAA’s updated 2021 Atlantic Hurricane Season Outlook indicates that an above-normal hurricane season is the most likely outcome with a possibility the season could be extremely active. The outlook indicates a 65% chance of an above-normal season, a 25% chance of a near-normal season, and a 10% chance of 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 2021 outlook calls for a 70% probability for each of the following ranges of activity:

  • 15-21 Named Storms
  • 7-10 Hurricanes
  • 3-5 Major Hurricanes
  • Accumulated Cyclone Energy (ACE) range of 110%-190% of the median
which includes the activity up this point (5 names storms, 1 hurricane, and the ACE contributions from those).

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 season is expected to produce above-average numbers of tropical storms, hurricanes, and major hurricanes. The centers of the predicted ranges of named storms, hurricanes, and major hurricanes (18, 9, and 4, respectively) are above the 1991-2020 seasonal averages of about 14 named storms, 7 hurricanes, and 3 major hurricanes.

Compared to the May outlook, the August update has a slight increase in the probability of above-normal activity and in the forecast ranges for likely seasonal counts of named storms and hurricanes. The range of predicted ACE is unchanged.

The ACE index measures the combined intensity and duration of all tropical storms and hurricanes during the season. NOAA uses this robust measure of overall seasonal activity to help classify hurricane season strength. The predicted ACE range is centered in the above-normal/active range. The range extends from the near-normal category (75-130% of median) into the above-normal category, and even exceeding the threshold for an extremely-active season (>165% of median).

b. Reasoning behind the outlook

The predicted 2021 activity reflects a continuation of the Atlantic high-activity era that began in 1995. Since the current Atlantic high-activity era began in 1995, 18 of 26 (about two-thirds) seasons have been above normal and only 4 (15%) have been below normal based on the 1951-2020 climatology of ACE. Most (10 out of the 18) of the above-normal years were hyper-active (ACE > 165% of median). There are some competing factors that could mitigate the overall activity despite the fact that the 2021 season featured the earliest 5th named storm on record. If average activity for August-November, as defined over 1991-2020, occurs over the remainder of the season, that would result in 17 named storms and 7 hurricanes overall. For the remainder of the season, we expect (with 70% probability for each range) an additional 10-16 named storms, with 6-9 becoming hurricanes and 3-5 of those becoming major hurricanes.

The continuation of the high-activity era is related to a set of conditions including lower wind shear, weaker trade winds, and stronger than average West African Monsoon. While ENSO-Neutral conditions are currently in place, it is somewhat likely that La Niña conditions will develop later in the season. Mitigating factors of near- or just slightly below-normal SSTs in the tropical Atlantic and above-normal sea-level pressures are currently observed.

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.


1. Expected 2021 activity

NOAA's outlook for the 2021 Atlantic Hurricane Season indicates that an above-normal hurricane season is most likely. The outlook indicates a 65% chance of an above-normal season, only a 25% chance of a near-normal season, and a 10% chance of a below-normal season. See NOAA definitions of above-, near-, and below-normal seasons.

The total seasonal activity is measured by NOAA’s Accumulated Cyclone Energy (ACE) index, which accounts for the combined intensity and duration of all named storms and hurricanes during the season. This outlook indicates a 70% chance that the 2021 seasonal ACE range will be 110%-190% of the median. This activity is the same as the prediction from May (110%-190% of the median ACE). Also, the updated ACE range is centered at 150% of median, which is above NOAA’s threshold (130% of median) for an above-normal season. Therefore, 2021 will likely extend the record of consecutive above-normal seasons to six.

The 2021 Atlantic hurricane season is now predicted to produce (with 70% probability for each range) a total of 15-21 named storms (which includes the five named storms to date), of which 7-10 are expected to become hurricanes(which includes the one hurricane to date), with 3-5 of these expected to become major hurricanes. These ranges are centered well above the 1991-2020 averages of about 14 named storms, 7 hurricanes and 3 major hurricanes.

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 updated 2021 Atlantic hurricane season outlook reflects competing factors, most of which support an above-normal season, but some point to more moderate outcomes.

  1. Atmospheric conditions now present within the MDR are generally conducive for hurricane development, and some of these conditions are predicted to last through the peak months of the hurricane season (August-October). The MDR spans the tropical Atlantic Ocean and Caribbean Sea (Goldenberg and Shapiro 1996). The underlying climate factor for these conditions is the ongoing Atlantic high-activity era, 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).

  2. There is about a 55% chance of La Niña during September-November (SON), and virtually no chance that El Niño will develop and suppress the hurricane activity this season. The combination of La Niña and a warm phase of the AMO typically results in weaker vertical wind shear in the MDR, which favors more activity. Currently, ENSO-neutral is being observed over the tropical Pacific, though the official CPC-IRI ENSO outlook suggests the development of La Niña during the latter portions of the Atlantic hurricane season. The West African Monsoon has been stronger than average with rains in June near the 80th percentile of historical observations. Additionally, the African Easterly Jet, as assessed at 700-hPa, has been shifted northward.

  3. Some observed conditions are not supportive of an active season. Near to slightly below-average sea-surface temperatures have been measured in portions of the tropical Atlantic for much of June and July. The comparison of tropical Atlantic sea-surface temperatures to the temperatures of the global tropics is part of the statistical tools used by the forecast team, and those tools would favor a near-normal, rather than above-normal season. Additionally, sea-level pressures have been generally above normal, a condition which does not enhance storm development.

  4. Enhanced June-July activity in the eastern Caribbean/tropical Atlantic (Hurricane Elsa) reinforces the expectation for an above-normal season. Historically, years with early-season activity in this region have a much higher likelihood of being above-normal

These expectations are based on extensive monitoring, analysis, and research activities, a suite of statistical prediction tools, and dynamical model forecasts. The dynamical model predictions come from the NOAA Climate Forecast System (CFS), NOAA Geophysical Fluid Dynamics Lab (GFDL) FLOR-FA and SPEAR-MED model, the United Kingdom Met Office (UKMET) GloSea5 model, and the European Centre for Medium Range Weather Forecasting (ECMWF) models. ENSO forecasts also use a combination of statistical and other dynamical models contained in the suite of Nino 3.4 SST forecasts, which is compiled by the IRI (International Research Institute for Climate and Society) and the NOAA Climate Prediction Center.

a. Long-term conditions and related circulations

An inter-related set of atmospheric and oceanic conditions, which is conducive for hurricane development, is now present in the MDR and some features are likely to continue through the peak of the hurricane season (August-September-October). The AMO is still positive, so the warm AMO conditions are likely to continue through the season and set a background for generally elevated activity. Of the set of conditions associated with the warm phase of the AMO, weaker vertical wind shear, weaker tropical easterly trade winds, a more conducive African Easterly Jet (AEJ), and a stronger West African Monsoon have been observed this year. Weak vertical shear is largely forecast to continue. This set of conditions allows for stronger African easterly waves, from which tropical storms and hurricanes can more easily develop (Bell and Chelliah, 2006). These storms then have an extended area with conducive conditions in which to intensify as they propagate westward over progressively warmer waters, and within an environment of reduced vertical wind shear, increased tropical moisture, and decreased atmospheric stability. The result is more, stronger, and longer-lived tropical storms and hurricanes.

Also in place is a more conducive African Easterly Jet. This wind pattern reflects weaker easterly winds (i.e., anomalous westerlies) along the equatorward flank of the AEJ axis. The resulting increase in cyclonic relative vorticity is more conducive to the intensification of African easterly waves, especially when that same environment features reduced vertical wind shear, increased moisture, and decreased atmospheric stability.

The above atmospheric conditions are all consistent with an enhanced West African monsoon system, which is an integral component of the warm AMO phase. The West African monsoon has been enhanced this summer, as indicated by negative velocity potential anomalies and enhanced upper-level divergence throughout the region. In fact, the monsoon rains have been well above average for several months, indicating an early start to the monsoon season as well.

b. La Niña or ENSO-neutral

Another climate pattern that can significantly impact Atlantic hurricane activity is the El Niño/ Southern Oscillation (or ENSO) (Gray 1984). ENSO is a coupled ocean-atmosphere phenomenon located over the central and eastern equatorial Pacific Ocean. ENSO has three phases: El Niño, Neutral and La Niña. El Niño, which refers to long periods (9-12 months) with above-average SSTs across the central and eastern equatorial Pacific, typically suppresses Atlantic hurricane activity. Conversely, La Niña, which refers to similar long periods with below average SSTs in the equatorial Pacific, typically enhances Atlantic hurricane activity. ENSO-neutral means no El Niño or La Niña.

The CPC classifies ENSO events and their strength using the area-averaged SST anomaly in the Niño 3.4 region, an area of the east-central equatorial Pacific between 120-170º W and 5ºN-5ºS. ENSO-neutral conditions are indicated by sustained Niño 3.4 region SST anomalies between -0.5ºC and +0.5ºC. ENSO-neutral conditions have been present this summer, but with generally below-average SSTs in the central tropical Pacific Ocean.

The CPC’s latest ENSO probability forecast issued in July predicts a 45% chance of La Niña during ASO, and about a 55% chance later in the season. These numbers have slightly increased from the forecast issued in May, which indicated about a 42% chance of La Niña during ASO 2021. The latest averages of the dynamical model predictions (thick red lines) now predict La Niña to develop during SON, while statistical models continue ENSO-Neutral. La Niña is classified by the Niño3.4 index of -0.5ºC or cooler, along with consistent atmospheric impacts.

Recent observations suggest that atmospheric and oceanic conditions continue to evolve toward La Niña. The latest weekly Niño 3.4 index value was -0.5 ºC, which is CPCs lower threshold for La Niña. The low-level winds across the Pacific are also aligned with La Niña conditions. Anomalous convection over the last month is more representative of ENSO-Neutral, so there is still some time before a linked atmospheric response would manifest over the Atlantic.

c. Current Seasonal Activity

Sea-surface temperatures over the Atlantic have been slightly below-average and cooler than the global tropics, which is not generally conducive for an active season. ERSST data shows that average SSTs in the MDR are 0.06ºC below the global tropical average. Tropical Atlantic SSTs are forecast to become closer to average or slightly above average by many of the dynamical models. Additionally, sea-level pressures have been generally above normal in the Atlantic during the last 45 days though pressures have been lower for portions of the eastern MDR. High resolution, developmental versions of the CFS contain predictions for sea-level pressures to remain above average for most of the region.

d. Mitigating Factors

The early portion of the 2021 season was more active than normal, with the earliest 5th named storm (Hurricane Elsa) on record (named July 1st). Basin wide, early season activity is generally not used directly as a predictor for overall seasonal activity as much of the early season activity can be subtropical or related to mid-latitude circulation features. All years with a hurricane formation in the MDR in June or July have ended with above-normal seasonal activity. Since Hurricane Elsa formed in the deep tropics during July, that is another predictive factor pointing to an above-normal season. Furthermore, historically 90% of the activity in a season occurs during ASO, so a fast start with the bulk of the season points toward an overall active season.


Climate Prediction Center

  • Matt Rosencrans, Physical Scientist; Matthew.Rosencrans{at}
  • Dr. Hui Wang, Physical Scientist; Hui.Wang{at}

National Hurricane Center

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

Hurricane Research Division

  • Stanley Goldenberg, Meteorologist; Stanley.Goldenberg{at}


  • 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.

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