Today is March 20 – the vernal (spring) equinox in the Northern Hemisphere. The start of spring is a reminder that the start of hurricane season will soon be upon us in just over two months. On June 1, the 2018 Atlantic hurricane season will officially begin, although there is about a 10 percent chance a storm could form before then. There is considerable uncertainty about how warm the tropical Atlantic will be during the peak of the season, as well as the state of the El Niño Southern Oscillation (ENSO). Currently, Weak La Niña conditions are present over the equatorial Pacific, although the La Niña is expected to dissipate within the next month or two. We currently expect a near average to slightly above average Atlantic hurricane season for 2018, based on the state of the Atlantic sea surface temperature anomaly pattern as well as the current evolution of the ENSO. However, with the well-documented ENSO Spring Predictability Barrier (SPB), our forecast remains somewhat uncertain.

Atlantic sea surface temperatures

Since 1995, the Atlantic basin has generally been in the active (positive) phase of the Atlantic Multidecadal Oscillation (AMO). Many of the most active Atlantic hurricane seasons in terms of Accumulated Cyclone Energy (ACE) have occurred during this time period, such as 1995, 2004, 2005 and 2017. All four of those Atlantic hurricane seasons featured an ACE of over 200, and were the four most active since Atlantic hurricane naming began in 1950. While it is unlikely we will see a season with quite the same activity as those four seasons, it does appear likely the general trend of increased Atlantic hurricane activity will continue into 2018.

Currently, sea surface temperatures are running slightly cooler than normal in the far eastern tropical Atlantic, and slightly warmer than normal in the western tropical Atlantic. Strong trade winds in January and February – typical of a La Niña winter – resulted in tropical Atlantic sea surface temperature anomalies returning to negative values, in contrast to the near-record warm temperatures observed in the tropical Atlantic during the hyperactive 2017 Atlantic hurricane season. During the month of March, however, a negative phase of the North Atlantic Oscillation (NAO) has resulted in the tropical Atlantic warming back up to near average levels. It is unclear how much the tropical Atlantic will warm during the months of April and May, and will likely be a major factor in determining how active the Atlantic Main Development Region (MDR) will be. It should be noted that at this time in 2017, the Atlantic MDR was running a bit below average in sea surface temperature anomalies, but this pattern quickly reversed in April and hurricane season forecast numbers were sharply adjusted upward.

While it is likely the Atlantic MDR will feature slightly above average sea surface temperatures at the peak of the 2018 Atlantic hurricane season, it is unlikely this part of the basin will be as warm or as active this season. It is also possible than warmer than normal water temperatures in the subtropical Atlantic may “rob” the tropical Atlantic of convective activity and suppress activity in the deep tropics. In 2017, within a span of less than a month, Hurricanes Irma, Jose and Maria all formed in this part of the basin and reached major hurricane intensity. This was somewhat unexpected after the relative quiet in the deep tropical Atlantic since 2012, in which only one major hurricane formed south of 20°N and east of 60°W (Danny in 2015). It is notable that the tropical Atlantic was so active in 2017, despite below-normal instability during much of the season.

El Niño Southern Oscillation (ENSO)

In March, weak La Niña conditions persisted over the equatorial Pacific, according to the NOAA Climate Prediction Center. The Climate Prediction Center (CPC) currently gives a 55% chance of La Niña transitioning back to ENSO-neutral conditions between March and May. Based on the CPC/IRI Official Probabilistic ENSO forecast (displayed above), there is approximately a 33% chance El Niño conditions will develop by the peak of the season, with a 67% chance El Niño conditions will not be present by that time. The latest weekly anomaly value for the Niño 3.4 region is -0.7°C. The CPC has not issued an El Niño watch, indicating that El Niño development is not imminent. El Niño conditions are typically associated with strong wind shear over the tropical Atlantic Ocean, especially the Caribbean Sea.

The main factor that makes the 2018 Atlantic hurricane season forecast so uncertain is the Spring Predictability Barrier (SPB). While an El Niño event does not appear to be the likeliest scenario, it is certainly a possibility. Climate models disagree over the state of ENSO by the peak of the season (August-September-October). The CFSv2 (Climate Forecast System) model predicts that cool neutral or weak La Niña conditions will be present by August-September-October 2018. On the flip side, the ECMWF model predicts that the Atlantic will most likely see warm neutral or weak El Niño conditions by that time. The ECMWF model, though very accurate in it short range predictions for tropical cyclones, has a high bias with forecasting ENSO. Last season, the model predicted moderate to strong El Niño conditions when El Niño did not develop at all. It is also likely that the CFSv2 model is too cool with its prediction, with the strong subsurface warm pool developing over the equatorial Pacific (more on this below). The dynamical and statistical model averages both show warm-neutral ENSO for the peak of the 2018 Atlantic hurricane season, with possibly weak El Niño conditions developing by late fall. It appears unlikely we will see a third consecutive year of La Niña conditions, but this possibility cannot be ruled out entirely.

The case for El Niño development is complicated. During the past few months, a downwelling Kelvin Wave over the western and central equatorial Pacific has resulted in a strong subsurface pool of warmer-than-normal sea surface temperatures developing, though it has weakened slightly over the past few weeks as it spreads eastward. Weak negative anomalies remain near the surface of the eastern Pacific,  but these negative anomalies are weakening. With a sizable westerly wind burst (WWB) in the next month or two, this warm water could be pushed eastward and ENSO could switch towards a warm-neutral or weak El Niño phase by June or July. However, if no westerly wind burst occurs, it would be very difficult to initiate El Niño development. As meteorologist Michael Ventrice recently noted on Twitter, the Atmospheric ENSO Index remains coupled to La Niña conditions, with a “warm pool” in the western Pacific. This is detrimental to the development of El Niño conditions. In addition, it is somewhat unusual to have such a rapid transition between El Niño and La Niña. In 16 years with La Niña conditions this late into the year, only three did El Niño conditions develop by the peak of hurricane season.

African monsoon

As has generally been the case since 1995, it is likely that the 2018 Atlantic hurricane season will enhanced tropical wave activity over west Africa. This is likely another positive factor for activity. The CFS and NMME models are both predicting that much of the Sahel region of western Africa will see above average rainfall for the peak of “Cabo Verde” season (July/August/September). With above average rainfall, we will likely see more frequent and perhaps more intense tropical waves. With stronger and/or more frequent tropical waves, it is more likely to see intense tropical cyclones over the tropical Atlantic, Caribbean and Gulf of Mexico.

Cyclonic Fury’s March 2018 Atlantic hurricane season forecast: 

• 11-16 named tropical storms (average: 12)
• 5-9 hurricanes (average: 6)
• 2-4 major (Category 3+) hurricanes (average: 3)
• Accumulated Cyclone Energy (ACE) 125 +/- 50 (average: ~95)

Cyclonic Fury also gives the following probabilities of activity. These have not changed much from our December forecast, with the exception of lowering the hyperactive chances and increasing the below average chances slightly due to the increased chance of an El Niño event since December.

• Hyperactive season: 15% (Accumulated Cyclone Energy (ACE) of 153 or greater, given the parameters of an above-normal season are also met. This is most likely if ENSO remains negative with very warm tropical Atlantic sea surface temperatures.)
• Above normal season: 35% (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. The most likely of the four scenarios, and will likely occur if ENSO remains neutral but the tropical Atlantic is slightly cooler than 2017.)
• Near normal season: 25% (Does not fall into the Below Normal, Above Normal or Hyperactive criteria. This will likely occur if tropical Atlantic sea surface temperatures are near to slightly above normal with no El Niño event, or tropical Atlantic sea surface temperatures are above normal with a weak El Niño event.)
• Below normal season: 25% (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 will most likely occur if an a moderate or strong El Niño event forms by the peak of hurricane season.)

Cyclonic Fury also considers the following four years to be good analogs for the 2018 Atlantic hurricane season. It should be stressed, however, that every season is different and nobody should expect a “repeat” of any season.

• 2000 – 15 named storms, 8 hurricanes, 3 major hurricanes
• 2006 – 10 named storms, 5 hurricanes, 2 major hurricanes
• 2009 – 9 named storms, 3 hurricanes, 2 major hurricanes
• 2012 – 19 named storms, 10 hurricanes, 2 major hurricanes

At this extended range, it is near impossible to predict which areas, if any, will have hurricane or tropical storm threats in 2018. The next Cyclonic Fury forecast for the 2018 Atlantic hurricane season will be released in mid-May 2018. By this time, we should have a much clearer idea on the ENSO forecast for the season as well as how warm tropical Atlantic sea surface temperatures will be.