The peak of the Atlantic hurricane season is quickly approaching. So far, the Atlantic basin has seen three tropical depressions and two named storms, including one minimal hurricane (Barry). Barry was the first July hurricane to make landfall in the United States since Arthur in 2014. Atlantic basin activity has been close to normal, though Barry reached hurricane strength about three weeks prior to the average date of the first hurricane formation in the Atlantic. Unlike the past two seasons, the Atlantic basin has not yet had a tropical cyclone form in the deep tropics. However, there are already signs that may change, with the National Hurricane Center (NHC) monitoring a tropical wave over the eastern Atlantic as of today.

This a slight increase from our May forecast. and significantly higher than our March forecast. Most importantly, El Niño is no longer expected to be in place for the peak of the Atlantic hurricane season. The Atlantic has transitioned to more of a +AMO look than two months ago, but the Atlantic MDR sea surface temperatures remain only near normal. However, a strong West African Monsoon may enhance Atlantic hurricane activity in the Atlantic MDR, regardless of the less than ideal base state.

Atlantic basin conditions over the last month

There have been mixed signals with regards to Atlantic tropical activity over the past month, none of which are an overwhelming signal for an active or an inactive season. The Atlantic sea surface temperature anomaly pattern is more typical of the positive phase of the Atlantic Multidecadal Oscillation (AMO) than the negative phase, with the monthly average showing a distinct anomalous warm horseshoe. However, the warm horseshoe is displaced north and east from that of a typical +AMO. The far north Atlantic is much warmer than average, typical of +AMO. On the flip side, the Atlantic Main Development Region (MDR) has been cooler than normal, especially right off Africa. Closer to the Lesser Antilles, MDR sea surface temperatures have been slightly warmer than normal over the past month. Overall, sea surface temperatures in the Atlantic MDR in the last month near normal, though much warmer than July 2018. In the most active Atlantic hurricane seasons, such as 1995, 2004, 2005, 2010 and 2017, the Atlantic MDR was much warmer at this time. Therefore, it is highly unlikely 2019 will be as active as those seasons. In the lower subtropics (around 20°N-30°N), sea surface temperatures are well above normal, which could “rob” the Atlantic MDR of upward motion, which could reduce tropical cyclone activity in the deep tropics. However, last year the MDR was even cooler and there was still a burst of tropical cyclone activity in the MDR in September, so I’d be surprised if we do not see at least a few tropical cyclones form in the Atlantic MDR despite the less-than-ideal base state.

Over the past month, vertical wind shear over the Atlantic basin has been near to slightly below average in the Atlantic MDR east of the Lesser Antilles (except right off the African coast, where it has been above average), slightly above average in the Caribbean, especially the central Caribbean, and generally below average in the subtropical Atlantic. Overall, this shear pattern looks typical for that of a decaying El Niño. The CFS and CanSIPS climate models suggest that the current strong shear over the Caribbean Sea is likely to lessen as the hurricane season progresses, due to continued cooling of the El Niño Southern Oscillation (ENSO) regions. Wind shear in the Caribbean has been much lower over the past month than typical El Niño years, though. This likely suggests that the Caribbean will most likely be fairly quiet early in the season, but activity could pick up there late in the season when it is climatogically favored. The below-normal wind shear in the subtropical Atlantic likely suggests this region will be above normal in overall activity once again, though likely not as active as 2018.

The big wild card for the activity of this season is mid-level dry air. Over the past month, the Atlantic MDR, subtropical Atlantic, and Caribbean Sea have all been much drier than normal at 600mb. Mid-level dry air can slow tropical cyclone development, especially when wind shear is not favorable. When wind shear is lower, however, tropical cyclones are often able to develop despite dry mid-level air, although they usually are quite small. It remains unclear how much mid-level dry air will be able to suppress activity, but the Atlantic MDR is much drier at the mid-levels than the most active seasons. In addition, instability over the Atlantic MDR and Caribbean has generally been below normal, likely as a result of the warmest sea surface temperature anomalies being farther north as noted above. Regardless, the Atlantic MDR has generally been drier than normal over the past decade or so, and 6 of the last 10 Atlantic hurricane seasons have been more active than normal.

El Niño Southern Oscillation (ENSO)

Officially, a weak El Niño event is still present, but the event appears to be coming to an end. Sea surface temperature anomalies over the last three weeks have been below +0.5°C in the Niño 3.4 region, which suggests the event is likely ending. El Niño events typically increase westerly vertical wind shear over the western Atlantic MDR and Caribbean. With no significant westerly wind bursts expected west of the International Date Line during August, it appears unlikely that El Niño conditions will return by the peak of the season. The latest CPC/IRI ENSO forecast calls for a 62% chance of neutral ENSO during ASO (August-September-October), with a 30% chance of El Niño persisting and only an 8% chance of La Niña developing. Overall, I think ENSO will not play a major suppressing role on the activity of the season. However, if ENSO cools more than expected, the season will likely be more towards the upper end of my forecast range. Sea surface temperature anomalies at the Pacific subsurface are currently near normal, which is not typical of El Niño.

The Southern Oscillation Index (SOI) has been consistently negative over the past three months, which suggests the atmosphere is still in an El Niño like state. However, the SOI can be noisy at times, and does not always greatly reflect the current ENSO trend. It appears highly unlikely that La Niña will develop by ASO, considering that we have not seen significant strong trade bursts over the dateline. Considering how the atmosphere has remained El Niño-like based on the SOI index, there remains an outside chance El Niño makes a comeback by late Autumn, but this would be too late to have an effect on the 2019 Atlantic hurricane season. The most likely outcome for ENSO is that it remains in the neutral range throughout the rest of the hurricane season, neither El Niño or La Niña.

West African Monsoon

Throughout July, the West African Monsoon has remained stronger than normal, which should enhance Atlantic basin activity. This has been reflected with above-normal precipitable water and precipitation in the Sahel region of Africa.

Over the past three months, the strong WAM has been reflected in Velocity Potential anomaly maps, with a persistent area of rising motion over Africa called a “standing wave.” Climate models, like the CanSIPS, have underestimated this standing wave over the last few months, resulting in models showing a drier Sahel region than actually observed. There has been a persistent sinking branch of positive velocity potential anomalies at 200 mb over the western Atlantic. While there has been a lot of talk about this “sinking branch” significantly suppressing activity, it is a common feature when there is rising motion over Africa, and has been present in some of the most active Atlantic hurricane seasons. I am skeptical that this sinking branch will significantly suppress activity in the Atlantic basin, as long as the African standing wave of -VP anomalies persists.

Where will the activity be?

I expect the greatest concentration of activity this season to be in the lower subtropics (around 20-30°N). The strong West African Monsoon likely means that we will see several tropical cyclones develop over the Atlantic MDR, even though the base state is not ideal for high activity in this region. The warmest anomalies in the subtropics are farther south than last season, which likely means that we will see fewer subtropical storms than 2018. The Caribbean may be more active than last season, especially if cool neutral ENSO emerges by Autumn.

One difference from July 2019 compared to recent years is that the subtropical ridge has been weaker. If this continues, it would favor more recurving storms and less westward moving storms. This is largely a result of a persistent negative North Atlantic Oscillation. However, the synoptic setup for every tropical cyclone is different, and you cannot make conclusions about where storms will go during the peak of the season.

Cyclonic Fury’s July 2019 Atlantic hurricane season forecast:

• 12-16 named storms (average: 12)
• 6-9 hurricanes (average: 6)
• 2-4 major hurricanes (average: 3)
• Accumulated Cyclone Energy 120 +/- 40 (average: 100)

Cyclonic Fury also gives the following probabilities of activity:

• Hyperactive season: 10% (Accumulated Cyclone Energy (ACE) of 153 or greater, given the parameters of an above-normal season are also met. A hyperactive season is not particularly likely this year, since the Atlantic SST pattern is not typical of a hyperactive season. However, it cannot be ruled out entirely if further MDR warming occurs in August, and ENSO cools to the cool neutral range.)
• Above normal season: 40% (Accumulated Cyclone Energy (ACE) of 112-152, with at least two of the following three parameters met or exceeded: 13 named storms, 7 hurricanes and 3 major hurricanes. This is the most likely scenario and will likely occur if the Atlantic remains in a similar state to now, along with neutral ENSO.)
• Near normal season: 30% (Does not fall into the Below Normal, Above Normal or Hyperactive criteria. This will likely occur if mid-level dry air and the sinking branch limit activity to some extent, but wind shear is low enough for several hurricanes to form.)
• Below normal season: 20% (Accumulated Cyclone Energy of 65 or below, or none of the following three parameters met or exceeded: 10 named storms, 5 hurricanes and 2 major hurricanes. This is not likely because El Niño is not expected to be in place, and the Atlantic MDR is not significantly cooler than normal.)

Cyclonic Fury also considers the following three years to be the best possible analogs for the 2019 Atlantic hurricane season. It should be stressed, however, that every hurricane season is different and nobody should expect a “repeat” of any season. 2019 is unusually tough to find analogs for, as it is rare to see an El Niño event dissipate during late summer as appears to be the case this season.

• 2003 – 16 named storms, 7 hurricanes, 3 major hurricanes
• 2004 – 15 named storms, 9 hurricanes, 6 major hurricanes
• 2014 – 8 named storms, 6 hurricanes, 2 major hurricanes
• Analog average – 13 named storms, 7.33 hurricanes, 3.67 major hurricanes

This is the last Cyclonic Fury seasonal forecast for the 2019 Atlantic hurricane season. The next seasonal forecast will be an early look at the 2020 Atlantic hurricane season, and will be released some time in December 2019. If you live in a hurricane-prone area, be sure to have a plan, as the peak of the season is quickly approaching!