NOAA 2019 Atlantic Hurricane Season Outlook

The updated 2019 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 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 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 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 climate conditions and uncertainties to those expected this year. The ranges do not represent the total possible 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 models that directly predict seasonal hurricane activity.

1. Although El Niño has dissipated, there is uncertainty as to how strong and persistent its impacts will be during the peak months (August-October, ASO) of the hurricane season. El Niño and La Niña are opposite phases of the El Niño-Southern Oscillation (ENSO), and both can significantly influence hurricane activity. Predicting these impacts is an ongoing scientific challenge facing climate scientists today. Such forecasts often 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. Model predictions of sea surface temperatures (SSTs), vertical wind shear, moisture, atmospheric stability, and other factors known to influence overall seasonal hurricane activity have limited skill, especially during periods of significant ENSO evolution.
   
   
4. Weather patterns that are unpredictable on seasonal time scales can sometimes develop and last for weeks or months, possibly affecting seasonal hurricane activity.
   
   

2019 Atlantic Hurricane Season Outlook: Summary

a. Predicted Activity

NOAA's updated outlook for the 2019 Atlantic Hurricane Season indicates that an above-normal season has the highest chance of occurring (45%), followed by a 35% chance for near-normal season and a 20% chance for a below-normal season. This outlook reflects the potential for more activity than was predicted in NOAA's pre-season outlook issued on 23 May. 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.

• 10-17 Named Storms
• 5-9 Hurricanes
• 2-4 Major Hurricanes
• Accumulated Cyclone Energy (ACE) range of 85%-165% 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 ranges of activity seen in past similar years. These expected ranges are centered at or above the 1981-2010 seasonal averages of 12 named storms, 6 hurricanes, and 3 major hurricanes. Most of the activity is predicted to occur during the peak months (August-October, ASO) of the hurricane season.

To date, the 2019 Atlantic hurricane season has produced two named storms (one each in May and July), with Hurricane Barry making landfall in Louisiana in July. For the remainder of the season, we expect an additional 8-15 named storms, with 4-8 becoming hurricanes and 2-4 of those becoming major hurricanes.

Changes from the pre-season outlook issued on 23 May 2019

Current and predicted conditions now indicate that the 2019 Atlantic hurricane season could be more active than was predicted in May. Compared to the May outlook, the likelihood of an above-normal season has increased from 30% to 45%. The likelihood of near-normal activity has dropped from 40% to 35%, and the likelihood of a below-normal activity has dropped from 30% to 20%.

The predicted numbers of named storms, hurricanes, and seasonal ACE have also increased from the May outlook (which indicated likely seasonal ranges of 9-15 named storms, 4-8 hurricanes, 2-4 major hurricanes, and an ACE range of 65%-140% of the median). These may not seem like large changes, but they certainly show the guidance has shifted towards a more active season.

Reason why the season could now be more active than was predicted in May

The main reason why the season could be more active is that El Niño dissipated during July, and ENSO-neutral conditions (i.e., No El Niño or La Niña) are now present. El Niño's lingering impacts are expected to fade over the next few months, but to still have a suppressing influence (via stronger vertical wind shear, anomalous sinking motion and increased atmospheric stability) on Atlantic hurricane activity during at least a portion of the ASO season. Overall, however, this suppressing influence is now expected to be weaker and of shorter duration compared to what was anticipated in the May outlook, when there was a 60% chance of El Niño persisting through the ASO season.

Therefore, these conditions are less likely to markedly offset those which favor increased activity in association with the ongoing high-activity era for Atlantic hurricanes. As a result, overall atmospheric conditions are predicted to be more conducive to above-normal activity than had been predicted in May.

The predicted ranges of hurricane activity reflect uncertainty in model forecasts for how long and strong El Niño's lingering impacts will be. Stronger and/or longer-lasting impacts could result in activity near the lower end of the predicted ranges, while weaker and/or shorter-lasting impacts could favor activity near the upper end of the predicted ranges.

Preparedness for Tropical Storm and Hurricane Landfalls:

It is important to remember that 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.

DISCUSSION

1. Expected 2019 activity

NOAA's updated outlook for the 2019 Atlantic Hurricane Season indicates that an above-normal season has the highest chance of occurring (45%), followed by a 35% chance for near-normal season and a 20% chance for a below-normal season. This outlook reflects the potential for more activity than was predicted in the pre-season outlook issued on 23 May. 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 all named storms and hurricanes during the season. This updated outlook indicates a 70% chance that the seasonal ACE range will be 85%-165% of the median. According to NOAA's hurricane season classifications, an ACE value between 71.4% and 120% of the 1981-2010 median reflects a near-normal season. Values above (below) this range reflect an above-normal (below-normal) season.

The 2019 Atlantic hurricane season is predicted to produce (with 70% probability for each range) 10-17 named storms, of which 5-9 are expected to become hurricanes, and 2-4 of those are expected to become major hurricanes. These ranges are centered at or above the 1981-2010 period averages of about 12 named storms, 6 hurricanes and 3 major hurricanes.

To date, the 2019 Atlantic hurricane season has produced two named storms (one each in May and July), with one becoming Hurricane Barry. For the remainder of the season, we expect an additional 8-15 named storms, with 4-8 becoming hurricanes and 2-4 of those becoming major hurricanes. [The August-November seasonal averages are about 10 named storms, 6 hurricanes and 3 major hurricanes.]

Predicting the location, number, timing, and intensity of landfalling hurricanes 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 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 hurricane this season.

2. Science behind the 2019 Outlook

NOAA's 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) FLOR model, 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. El Niño forecasts are also provided by statistical and other dynamical models contained in the suite of Niño 3.4 SST forecasts, which is compiled by the International Research Institute for Climate and Society (IRI) and the NOAA CPC.

Current conditions and model forecasts still point to competing factors during at least a portion of the ASO period. However, because El Niño has now dissipated, the suppressing factors are now expected to be weaker and of shorter duration compared to the May outlook, thus increasing the likelihood of a more active hurricane season.

This change in the outlook mainly reflects a reduction in both the predicted magnitude and duration of El Niño's suppressing influence on Atlantic hurricane activity. El Niño typically suppresses the activity by causing increased vertical wind shear (Gray 1984), anomalous sinking motion, and increased atmospheric stability across the western portion of the Atlantic hurricane Main Development Region. The MDR, spans the tropical Atlantic Ocean and Caribbean Sea (Goldenberg and Shapiro 1996). The recent dissipation of El Niño and a predicted reduction in its impacts, combined with conducive conditions associated with the ongoing high-activity era for Atlantic hurricanes, results in a higher likelihood of an above-normal season and a reduced likelihood of a below-normal season.

a. ENSO-neutral (i.e., No El Niño or La Niña) is most likely during ASO 2019

El Niño developed late in 2018 and dissipated in July 2019. Equatorial SSTs remain above average in the central Pacific, but are currently near average across the east-central Pacific and below average in the eastern Pacific. The areal extent of the anomalous warmth is now much less than was observed in May. Consistent with this evolution, tropical convection and oceanic heat content have both returned to near average across the eastern half of the Pacific Ocean.

However, there is some variability in model forecasts for the next several months. The average of the dynamical model predictions for the Niño 3.4 region indicates ENSO-neutral through the remainder of the year, while the average of the statistical models predicts a weak El Niño. [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.] Based on the recent oceanic evolution and the spread in model forecasts, NOAA's latest ENSO outlook indicates a 65%-70%% chance of ENSO-neutral during ASO, and only a 25%-30% chance of El Niño.

Dynamical predictions from NOAA's CFS and GFDL models, and forecasts from the NMME, all predict the below-average SSTs in the eastern Pacific to expand westward throughout the Niño 3.4 region during ASO, and to eventually erode the positive SST anomalies near the date line. The CFS models have the most aggressive cooling, with both the Hi-Res and Low-Res models predicting the development of a weak La Niña by October. The variations in model predictions for El Niño, and for its impacts on the vertical wind shear, produce uncertainty in this hurricane outlook.

b. Predicted conditions in the MDR

SSTs are currently above average in the central and western MDR, and below average near Africa. The For the MDR as a whole SSTs during July were about 0.2°C above average. Climate models predict near- or slightly above-average SSTs during ASO, with most models predicting departures of around 0.2°C.

In the atmosphere, competing factors are currently present. Conditions over the eastern MDR and western Africa favor increased activity, and are associated with the ongoing high-activity era for Atlantic hurricanes that began in 1995 (Goldenberg et al. 2001, Bell and Chelliah 2006, Klotzbach and Gray 2008). Conversely, conditions in the western MDR are consistent with reduced activity typically seen during El Niño.

Four inter-related atmospheric features are now present in the eastern MDR and western Africa in association with the ongoing high-activity era, and they are expected to persist. These factors include 1) an enhanced West African monsoon system, 2) anomalous westerly winds at 700-hPa and a more conducive African Easterly Jet, 3) an enhanced upper-level ridge, and 4) decreased vertical wind shear. These conditions directly contribute to increased hurricane activity in the eastern MDR.

In contrast, in the western MDR anomalously strong vertical wind shear and anomalous sinking motion have been present in association with El Niño. El Niño has now dissipated, and dynamical models predict a lessening of El Niño's impact on the vertical wind shear during ASO. The CFS Hi-Res and NMME models are predicting the anomalously strong shear to become confined to the western Caribbean Sea. The CFS Low-Res model is predicting near-average shear in that region, while the GFDL model is predicting below-average shear. Also, all four models are predicting below-average vertical wind shear across the northern MDR extending northward across the subtropical North Atlantic.

The activity within the MDR during ASO is the main contributor to the overall activity of the hurricane season. The combination of a more rapid demise of El Niño's lingering impacts, warmer SSTs in the MDR, weaker vertical wind shear, and a stronger West African monsoon favors hurricane activity near the upper ends of our predicted ranges. Conversely, if El Niño's lingering impacts are protracted and stronger, this would favor activity in the lower portion of the predicted ranges.

• Dr. Gerry Bell, Lead Forecaster, Meteorologist; Gerry.Bell@noaa.gov
• Matt Rosencrans, Meteorologist; Matthew.Rosencrans@noaa.gov
• Dr. Hui Wang, Physical Scientist; Hui.Wang@noaa.gov

• Eric Blake, Hurricane Specialist; Eric.S.Blake@noaa.gov
• Dr. Chris Landsea, Meteorologist; Chris.Landsea@noaa.gov
• Dr. Richard Pasch, Hurricane Specialist; Richard.J.Pasch@noaa.gov

• Stanley Goldenberg, Meteorologist; Stanley.Goldenberg@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.

• 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.