Cyclonic Fury has released our May 2018 Atlantic hurricane season forecast update. We have lowered our numbers slightly since the March forecast. Cyclonic Fury now anticipates 10-14 named storms to form during the 2018 Atlantic hurricane season, along with 4-7 hurricanes and 2-3 major hurricanes. This updated outlook calls for a 75% probability of near or below average activity. This forecast reduction is based on two primary factors: cooler tropical Atlantic sea surface temperatures and a moderate chance for a weak El Niño to form late in the year.

Atlantic sea surface temperatures

For the most part since 1995, the Atlantic has been generally in the positive/active phase of the Atlantic Multidecadal Oscillation (AMO). However, the current Atlantic sea surface temperature (SST) pattern is much different than what is typically seen during active hurricane seasons. Sea surface temperatures over the tropical Atlantic have remained anomalously cool, along with sea surface temperatures over the subtropical Atlantic remaining above average – this pattern is generally consistent with the negative phase of the AMO. This reverse of the Atlantic SST pattern from last season has been caused by a persistently positive North Atlantic Oscillation (NAO), which has resulted in strong easterly trade winds over the tropical Atlantic, keeping it cooler than normal. Because of the current unfavorable Atlantic SST pattern, it is highly unlikely that this hurricane season will be as active as last year. The tropical Atlantic is much cooler than the global tropics average.

It is far too soon to make conclusions that the next cool phase of the AMO has begun. Global models predict that the tropical Atlantic may warm to near average by the August-September-October (ASO) peak period, but the subtropical Atlantic is expected to remain warm, which would likely suppress convective activity over the deep tropical Atlantic. Overall, the Atlantic SST pattern looks less than ideal for an active Atlantic hurricane season, especially in the tropical latitudes.

ENSO/PDO/PMM

In addition to the unfavorable Atlantic sea surface temperature anomaly pattern, the chances of an El Niño forming this year have increased slightly since March. La Nina conditions dissipated in April, and the El Niño Southern Oscillation (ENSO) has since returned to neutral conditions. A slow but steady warming is expected in the Niño 3.4 region between now and the end of the year, and the region is likely to approach weak – possibly “Modoki” El Niño conditions by autumn. However, it is unlikely that El Niño, if it develops, will become a strong event. The development of El Niño is still not quite certain, since the warmest anomalies in the subsurface have remained nearly stationary since late March. Since El Niño is not likely to develop until late in the year, it will likely have little effect on the first half of the season, but could play a suppressing role late in the season.

El Niño development appears unlikely in the short term. Although there is a pool of anomalously warm water at the subsurface of the equatorial Pacific, the warmest anomalies (about 3-4°C above average) remain near the central Pacific and have moved little in the past two months. In addition, the Southern Oscillation Index (SOI) has not been persistently negative, indicating that the pressure pattern is not favoring El Niño yet. With the Madden-Julian Oscillation (MJO) expected to progress into phases 4 and 5, this favors easterly trade winds near the International Dateline, making warming across the ENSO regions difficult. With the trade burst expected over the equatorial Pacific in the short term, an upwelling Kelvin Wave could develop, which could result in a pool of cooler than normal water temperatures forming beneath the surface – which would make El Niño development less likely.

The Pacific Meridonial Mode (PMM) is also strongly positive. +PMM phases usually lead to increased hurricane activity over the eastern Pacific basin, which would, in turn, induce subsidence across the tropical Atlantic. Even if El Niño does not form, the strong positive PMM could be a negative factor that could limit tropical activity across the Atlantic. In contrast, the Pacific Decadal Oscillation (PDO) has been weakly negative in recent months. This could be a slight enhancing factor for the Atlantic, but it should be noted that global models suggest that the PDO could turn more positive this summer and fall as the ENSO regions warm.

African Monsoon

A likely enhancing factor for the 2018 Atlantic hurricane season is expected above normal rainfall in the Sahel region of Africa during the July-August-September period, which would lead to stronger tropical waves. Stronger tropical waves are more likely to develop into tropical cyclones, and may be able to survive the tropical Atlantic even if it is very hostile. It should be noted that, despite the strong waves, most climate models are predicting a drier than normal tropical Atlantic, which would mean that waves would struggle to get going over the deep tropics. The expected strong African monsoon is primarily why I have stopped short of predicting a below average season.

Where will the activity be?

I expect activity this year to be the greatest in the Gulf of Mexico and Subtropical Atlantic, where I expect near to perhaps above average activity. In the Atlantic Main Development Region (MDR) and Caribbean Sea, I expect activity to be slightly below average, possibly well below average near the Lesser Antilles and Eastern Caribbean. The Atlantic MDR (the tropical Atlantic between the Lesser Antilles and Africa) is currently significantly cooler than normal, and is expected to be very dry during the peak of the season. Tropical waves, despite expected to be strong, are likely going to struggle to develop in this region due to hostile conditions. It is worth noting that many similar seasons to 2018 have often seen storms quickly developing near the Cabo Verde Islands, but these storms often weaken as they run into hostile conditions farther west. The subtropical Atlantic is currently very warm, and I expect above average activity in this region. Tropical waves unable to develop over the deep tropical Atlantic may find better conditions over the subtropical Atlantic north of 25°N.

It is nearly impossible to predict exactly which areas will get hit by tropical cyclones in a pre-season forecast, but it is possible to analyze which areas have a greater and lower risk looking at the expected basin activity. I would generally say that the Eastern Gulf Coast and East Coast of the United States, the Bahamas as well as Bermuda, may have a slightly enhanced risk for a storm this year due to the very warm subtropical Atlantic. The Lesser Antilles, Greater Antilles (including Puerto Rico), and the Yucatan Peninsula will likely have a lower risk for a tropical cyclone landfall this season, due to the expected hostile deep tropics. I would say that the risk of a tropical cyclone affecting mainland Mexico is near average. It must be stressed that, even if conditions are generally unfavorable during a season, it only takes a short window of favorable conditions for a storm to intensify and affect a region!

Cyclonic Fury’s May 2018 Atlantic hurricane season forecast:

• 10-14 named tropical storms (average: 12)
• 4-7 hurricanes (average: 6)
• 2-3 major (Category 3+) hurricanes (average: 3)
• Accumulated Cyclone Energy (ACE) 90 +/- 25 (average: ~95)

Cyclonic Fury also gives the following probabilities of activity. I have lowered the probability of a hyperactive or above normal season, and increased the probability of a near normal or below normal season – primarily due to the unfavorable Atlantic SST pattern and possible weak El Niño.

• Hyperactive season: 5% (Accumulated Cyclone Energy (ACE) of 153 or greater, given the parameters of an above-normal season are also met. This is highly unlikely, and would likely only occur if the tropical Atlantic unexpectedly warmed significantly to above normal levels during the summer months with ENSO remaining neutral.)
• 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 could occur if the MDR warms to about average, and no El Niño forms during the season.)
• Near normal season: 35% (Does not fall into the Below Normal, Above Normal or Hyperactive criteria. This will likely occur if tropical Atlantic sea surface temperatures are  below normal with no El Niño event, or tropical Atlantic sea surface temperatures are above normal with a weak El Niño event.)
• Below normal season: 40% (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 the tropical Atlantic remains very cool, and El Niño forms by the peak of the 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.

• 1994 – 7 named storms, 3 hurricanes, 0 major hurricanes
• 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

Overall, Cyclonic Fury expects activity to be close to average, but much quieter than last year. It should be stressed that, even in a quiet season, it only takes one storm to have a significant impact. If you live in a hurricane-prone area, be sure to have a hurricane plan this season, even though it may not be a very active season!