The 2019 Atlantic hurricane season will officially begin on June 1. So far, one named storm has formed in the North Atlantic basin in 2019 – Andrea. Now that it is May, the forecast has become clearer, and Cyclonic Fury now expects a more active season than our March forecast. This is primarily because El Niño has not strengthened over the last two months, and climate models have backed off their ENSO forecast. In addition, the equatorial Pacific subsurface has cooled significantly, with the subsurface sea temperature anomaly now negative. The tropical Atlantic is also much warmer than at this time last year, though still significantly cooler than most very active seasons in May.

Atlantic Sea Surface Temperature Anomalies

After three consecutive above-average hurricane seasons, the Atlantic basin still appears to be in an active phase of hurricane activity that began in 1995. During the active era of Atlantic hurricane activity, the Atlantic basin most commonly has a sea surface temperature (SST) anomaly pattern known as a positive Atlantic Multidecadal Oscillation (+AMO). In a +AMO pattern, the tropical Atlantic and far north Atlantic are warmer than normal, while the SST anomaly in the subtropical Atlantic is cooler than that of the deep tropics. Right now, the Atlantic sea surface temperature profile does not strongly resemble a +AMO or a -AMO pattern. The far North Atlantic is cooler than normal, the subtropical western Atlantic is much warmer than normal, and the tropical Atlantic is very close to normal. This is in contrast to May 2017, when a defined +AMO pattern was present, and May 2018, when a strong -AMO pattern was present. While a cooler than normal far North Atlantic is usually associated with -AMO, the far north Atlantic has been consistently cooler than normal the last three years, and has had little suppressing effect on the hurricane season.

Most climate models predict the tropical North Atlantic will be slightly warmer than normal at the peak of the hurricane season (August-September-October), including the NMME multi-model consensus. This should have a relatively neutral, if not a slight enhancing, effect on the hurricane season. However, it is not even close to as warm as the very warm tropical Atlantic of hyperactive seasons such as 2005, 2010 and 2017. It is worth noting last year that despite a significantly colder than normal tropical Atlantic for much of the first half of hurricane season, the tropical Atlantic produced six named storms and four hurricanes. It is also worth nothing that 2005, a hyperactive season with a very warm tropical Atlantic, only featured two hurricanes in the tropical Atlantic east of 60°W. This proves that sea surface temperature anomalies alone are not always a great predictor for activity in the eastern tropical Atlantic. The strength of the West African Monsoon (WAM), as well as the strength of the Saharan Air Layer (SAL) are other variables that influence activity in this region.

El Niño Southern Oscillation (ENSO)

Weak El Niño conditions remain present over the equatorial Pacific. The latest Nino 3.4 sea surface temperature anomaly was estimated at +0.7°C, which is slightly warmer than last week but cooler than in March. At the time of our March forecast, it appeared as if El Niño would very likely persist and strengthen, because there was an impressive pool of subsurface warmth and the atmosphere appeared to finally be coupling with the ocean. However, as the warm pool began to reach the surface, a strong easterly trade burst occurred, which weakened the warm pool significantly and triggered an upwelling Kelvin Wave, which resulted in a small pool of cooler than normal water forming underneath the warm pool. The El
Niño has made an attempt to persist, with a westerly wind burst occurring near the International Date Line in early May. This appeared to trigger a weak Downwelling Kelvin Wave, which could result in the formation of a new pool of warmer than normal water in the subsurface. So far, this is yet to occur, and without assistance from a Western Pacific typhoon, the westerly wind burst likely did not trigger as strong of a downwelling Kelvin Wave as it needed for the El Niño to strengthen significantly. It does appear as if there are no new upwelling Kelvin Waves developing, and we will likely not see any significant easterly wind bursts over the equatorial Pacific in the near future. Due to this, a transition to cool ENSO (such as a La Niña event) appears unlikely at this time.

The May plume of model Niño 3.4 mean sea surface temperature anomaly mean remains over +0.5°C for the August/September/October (ASO) timeframe, though there has been a trend downward from previous forecasts. While it is certainly possible a weak El Niño will persist through fall, it is looking unlikely that we will even see a moderate event at this point. It is also certainly possible we see a transition to warm ENSO-neutral conditions by fall if the current downwelling Kelvin Wave is unable to significantly warm the subsurface.

The ENSO is in a strange state, and is showing mixed signals. The subsurface pattern looks very much like a dissipating El Niño, but the atmosphere remains very much El Niño-like. The 90-day average of the Southern Oscillation Index (SOI), an index used to measure how the atmosphere is responding to ENSO, was at -5.56, indicative of borderline weak El Niño conditions. Normally, prior to a transition to cool ENSO, we would see the SOI turn positive, and we would see stronger and more frequent upwelling Kelvin Waves than we have seen so far. Right now, I do think El Niño could slightly reduce early-season activity in the tropical Atlantic (especially the eastern Caribbean), but I do not think it will lead to a well below average season like stronger +ENSO events often do. Also, this event does appear to be more central-based than east-based, which generally does not result in wind shear as high in the tropical Atlantic as east-based events.

West African Monsoon (WAM)

The strength of the West African Monsoon is a factor that is used to determine the amount of activity in the eastern tropical Atlantic. Last year, the WAM was significantly stronger than normal, allowing six named storms to form in the tropical Atlantic, which was cooler than normal for most of the season. When the WAM is strong, you get stronger tropical waves that develop faster.

So far, based on above-normal precipitable water over Africa’s Sahel region, and a persistent negative velocity potential anomaly (upward motion) over Africa since the start of 2019, it appears likely that the WAM will be stronger than normal once again this year. Since the WAM is likely to be strong, we will likely see at least near average activity in the tropical Atlantic, possibly above average activity if the tropical Atlantic warms further. A strong WAM also can reduce the trade winds in the eastern tropical Atlantic, allowing the region to warm further into the season. I expect the WAM to have an enhancing effect on the 2019 Atlantic hurricane season.

Cyclonic Fury’s May 2019 Atlantic hurricane season forecast

• 11-15 named storms (average: 12)
• 5-8 hurricanes (average: 6)
• 1-3 major hurricanes (average: 3)
• Accumulated Cyclone Energy 105 +/- 40 (average: 95)

Cyclonic Fury also gives the following probabilities of activity. Right now, we think a near to slightly above average season is likely, but the forecast remains uncertain due to ENSO uncertainty and how warm the tropical Atlantic will be come the peak of the season.

• Hyperactive season: 10% (Accumulated Cyclone Energy (ACE) of 153 or greater, given the parameters of an above-normal season are also met. This remains a very unlikely scenario, and would likely only be possible if ENSO goes into cool neutral by peak and the tropical Atlantic warms to much above average levels.)
• Above normal season: 20% (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 will likely occur if ENSO goes neutral and the West African Monsoon (WAM) is strong, or if the subtropical Atlantic is once again very active like it was in 2018.
• Near normal season: 40% (Does not fall into the Below Normal, Above Normal or Hyperactive criteria. This will likely occur if ENSO remains around the El Niño threshold, and the Atlantic sea surface temperature anomaly profile does not change much by the peak of the season.
• Below normal season: 30% (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 likely occur if El Niño is able to persist and restrengthen by the peak of the season.
  

Cyclonic Fury also considers the following four 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. The ENSO is also more uncertain than usual at this point in the season, so the analogs are just for guidance.

• 1969 – 18 named storms, 12 hurricanes, 5 major hurricanes
• 2003 – 16 named storms, 7 hurricanes, 3 major hurricanes
• 2014 – 8 named storms, 6 hurricanes, 2 major hurricanes
• 2018 – 15 named storms, 8 hurricanes, 2 major hurricanes
• Analog average – 14.25 named storms, 8.25 hurricanes, 3 major hurricanes

At this extended range, it remains near impossible to predict which areas, if any, will have hurricane or tropical storm threats in 2019. The next Cyclonic Fury forecast for the 2019 Atlantic hurricane season will be released on July 30, 2019. By that time, we should have a better idea on which specific regions of the Atlantic basin will be active.