The 2021 Atlantic hurricane season officially begins a week from today, June 1. However, we have already seen one named storm form: Tropical Storm Ana, which formed northeast of Bermuda on Saturday and became a remnant low late Sunday night. Ana’s formation marked the seventh straight year with a pre-season named storm in the Atlantic basin. While tropical cyclogenesis appears unlikely for at least the next 7-10 days in the Atlantic basin, Cyclonic Fury is forecasting yet another above-average Atlantic hurricane season in 2021. It appears unlikely that El Niño conditions will be in place for the peak of the hurricane season, and the Atlantic sea surface temperature anomaly pattern is somewhat similar to last year but not particularly similar to other recent hyperactive seasons. Overall, our forecast has not changed much from March.

Atlantic Sea Surface Temperatures

Overall, the sea surface temperature anomaly pattern in the Atlantic basin does not resemble the positive or negative phase of the Atlantic Multidecadal Oscillation (AMO). Over the past month, sea surface temperatures in the tropical Atlantic and Caribbean have been near to slightly-below average, while sea surface temperatures over the entire subtropical Atlantic have been well above average. While anomalously sea surface temperatures in the western subtropical Atlantic in May are not correlated with active Atlantic hurricane seasons, anomalously warm sea surface temperatures in the eastern subtropical Atlantic are. Although the Atlantic sea surface temperature pattern may not be typical of a positive AMO, the active Atlantic hurricane era that began in 1995 still appears to be in full swing, so I am not expecting it to have a significant detrimental effect on the Atlantic hurricane season. It also remains a possibility that the above-normal sea surface temperatures in the eastern subtropical Atlantic could migrate southward into the tropical Atlantic if trade winds are anomalously weak over the coming months. While this sea surface temperature pattern does not resemble the composite of recent hyperactive Atlantic hurricane seasons, it is very close to last year, which became the most active Atlantic hurricane season on record in terms of named storms. Overall, I would expect the Atlantic sea surface temperature anomaly pattern to have a neutral to slightly enhancing effect on Atlantic hurricane activity this season.

El Niño Southern Oscillation (ENSO)

La Niña conditions have recently dissipated over the equatorial Pacific, as the Climate Prediction Center recently declared the 2020-21 La Niña event over. The latest weekly Niño 3.4 sea surface temperature anomaly value was -0.2°C, which is in the neutral range. This is the warmest sea surface temperature anomaly value for the Niño 3.4 region since June 2020. The 90-day average of the Southern Oscillation Index has decreased to +1.65, which is also consistent with ENSO-neutral. Since mid-March 2021, subsurface sea surface temperature anomalies have been warmer than average over the equatorial Pacific, which suggests it is unlikely La Niña redevelops in the immediate future. It would not be terribly surprising to see ENSO reach warm-neutral territory this summer, even if only briefly. The May CPC/IRI probabilistic forecast gives a 50% chance of ENSO-neutral, a 42% chance of La Niña, and only an 8% chance of El Niño for August-September-October 2021. However, the May CPC/IRL model-based forecast has significantly higher chances of El Niño, with a 55% chance of ENSO-neutral, a 24% chance of La Niña, and a 21% chance of El Niño – a high enough chance to where it must be considered as a possibility. Even in the unlikely event that El Niño does develop by Northern Hemisphere fall, it would likely be too weak and too late to have a significant suppressing effect on the 2021 Atlantic hurricane season. Without El Niño, it is unlikely that there will be persistent strong shear over the deep tropical Atlantic during the peak of the season. Therefore, I expect ENSO to have a slightly enhancing effect on the 2021 Atlantic hurricane season.

West African Monsoon

Based on the recent above-normal precipitable water over Africa, it appears likely that the recent trend of a strong West African Monsoon (WAM) will continue this year. Rainfall in the Sahel region of Africa has consistently been above-normal in recent years, and climate models, including the NMME model blend, show that happening again this year during the July-October period. With above-normal precipitation likely over Africa, it appears as if the strong West African Monsoon will have an enhancing effect on the 2021 Atlantic hurricane season. However, it is also a possibility if the WAM is too strong, it could lead to large disturbances that are slower to consolidate, which would decrease the chance of MDR (Main Development Region) long-track hurricanes, like we saw in 2020.

Cyclonic Fury’s May 2021 Atlantic hurricane season forecast update

• 15-20 named storms (1991-2020 average: 14.2)
• 7-10 hurricanes (1991-2020 average: 7.2)
• 3-5 major (Category 3+) hurricanes (1991-2020 average: 3.2)
• Accumulated Cyclone Energy 140 (+/- 40) (1991-2020 average: ~122)

Cyclonic Fury also gives the following probabilities of activity. Since NOAA has recently switched to using 50-year-averages for Accumulated Cyclone Energy, I will use 50-year averages for this metric as well, because of the recent high bias in the 1991-2020 period due to it being mostly in an ongoing active era.

• Hyperactive season: 25% (Accumulated Cyclone Energy (ACE) of 160 or greater. This will likely occur if anomalous tropical Atlantic warming occurs during the next few months, and ENSO is cool neutral or weak La Nina during the peak.)
• Above normal season: 40% (Accumulated Cyclone Energy (ACE) of 126-159. This is the most likely scenario and assumes that the near-average MDR will slightly damper activity compared to the most hyperactive seasons, or ENSO remains warm-neutral during the peak with a warm MDR).
• Near normal season: 20% (Does not fall into the Below Normal, Above Normal or Hyperactive criteria. This scenario could occur if the Atlantic MDR remains near-average and ENSO is warm-neutral during the season.)
• Below normal season: 15% (Accumulated Cyclone Energy (ACE) of 73 or less. This is an unlikely scenario, but could occur in the unlikely event that El Nino develops before the fall.)

Cyclonic Fury also considers the following four years to be the best possible analogs for the 2021 Atlantic hurricane season. It should be stressed, however, that every hurricane season is different and nobody should expect a “repeat” of any season. 

• 2001 – 15 named storms, 9 hurricanes, 4 major hurricanes
• 2008 – 16 named storms, 8 hurricanes, 5 major hurricanes
• 2011 – 19 named storms, 7 hurricanes, 4 major hurricanes
• 2017 – 17 named storms, 10 hurricanes, 6 major hurricanes
• Analog average – 16.75 named storms, 8.5 hurricanes, 4.75 major hurricanes

Cyclonic Fury May Forecasts Verification

This is the fifth year Cyclonic Fury has issued a May Atlantic hurricane season forecast. Our first May Atlantic hurricane season forecast was released in 2017, predicting 13 named storms, 6 hurricanes and 3 major hurricanes (excluding Tropical Storm Arlene). This forecast fell well short of the actual activity, which was 17 named storms, 10 hurricanes, and 6 major hurricanes. In May 2018, Cyclonic Fury began to use ranges as I do now, predicting 10-14 named storms, 4-7 hurricanes, 2-3 major hurricanes, and an ACE index of 90 +/- 25 units. This forecast, just like expert groups in 2018, fell well short of the actual activity of 15 named storms, 8 hurricanes, 2 major hurricanes and an ACE index of 130 units. In May 2019, Cyclonic Fury predicted 11-15 named storms, 5-8 hurricanes, and 1-3 major hurricanes, with an ACE index of 105 +/- 40 units. Atlantic hurricane activity verified higher than my forecast, as 18 named storms, 6 hurricanes, and 3 major hurricanes formed, with an ACE index of 130 units. However, I did correctly suggest that El Niño persisting was not a guarantee, while NOAA expected it to persist in May 2019. In May 2020, I correctly predicted an above-average to hyperactive season, predicting 15-19 named storms, 7-10 hurricanes and 3-5 major hurricanes. Once again, Atlantic hurricane activity verified higher than my forecast, with 30 named storms forming, 14 hurricanes and 7 major hurricanes. While Cyclonic Fury has under-forecast the past four Atlantic hurricane seasons, the same has been true for most expert groups aside from NOAA (and even NOAA was too low in 2020).