Welcome to Cyclonic Fury’s Daily Blog! From now until the end of November, I will add a blog post nearly every day about the latest news in tropical weather. Today is May 15 – and the Atlantic hurricane season officially begins in only 17 days.  Tropical cyclones form primarily in the Atlantic between June 1 and November 30 (the dates that are officially considered Atlantic hurricane season), however, they can form before or after these dates, as evidenced by Tropical Storm Arlene this past April. However, there is a major uptick in activity between roughly August 15 and October 20, and this is the period of the season in which most of the strongest hurricanes form.  Quiet periods outside of that stretch are very common – in fact, it is not uncommon at all for the months of June, July and November to have very little activity or no activity at all. For instance, last season, we had no named storms in July, and the season ended up well above average with 15 named storms, 7 hurricanes and 4 major hurricanes.

So what does the upcoming 2017 Atlantic hurricane season hold? Well, there is still a large range of possibilities with the upcoming season, and I’m going to go into detail about all of the factors that may come into play this season. The activity of this season will largely be dependent on the sea surface temperature pattern in the Atlantic Ocean and the evolution of the El Niño Southern Oscillation. Most models have been fairly consistent with above-normal sea surface temperatures in the tropical Atlantic Ocean as well as near to slightly above normal sea surface temperatures in the subtropical Atlantic Ocean. This sea surface temperature pattern usually favors above-normal hurricane activity in the Atlantic Ocean, and mostly resembles the positive phase of the Atlantic Multidecadal Oscillation (AMO) – a long-term oscillation of sea surface temperature anomalies in the Atlantic. While sea surface temperatures in the Atlantic should be somewhat favorable for tropical cyclone development, there is a large question mark looming for the season’s activity: and that is the El Niño Southern Oscillation as noted above.

The El Niño Southern Oscillation (ENSO) is a yearly oscillation of sea surface temperature anomalies in the equatorial Central and Eastern Pacific Ocean. The warm phase of the oscillation is known as El Niño, which usually results in increased wind shear and drier air across the Atlantic basin. The cool phase of the oscillation is known as La Niña, which usually results in lower wind shear and a more moist tropical Atlantic. Wind shear is unfavorable for the development of tropical storms and hurricanes because it limits their ability to “stack up” vertically and strengthen. In simpler terms, El Niño is usually unfavorable for Atlantic tropical storms and hurricanes, while La Niña is more favorable.  In many years, the oscillation is neither in an El Niño or La Niña state, known as “ENSO-neutral.” Currently, we are in an ENSO-neutral state, but some models (notably the ECMWF and CanSIPS) have indicated the possibility of development of El Niño later this summer or in the fall. A few months ago, more models had suggested this possibility, but recently the UKMET (UK Meteorological Office), CFSv2 (Climate Forecast System version 2) and Australian Bureau of Meteorology models have backed off the El Niño possibility or dropped it entirely. This means the El Niño Southern Oscillation could remain neutral during the peak of the 2017 Atlantic hurricane season, and the season could be more active than originally thought. Without the increased wind shear and drier environment caused by El Niño, an above-average Atlantic hurricane season is definitely a strong possibility.

On another note, long-range climate models have consistently shown above-average rainfall in the Sahel region of Africa where tropical waves develop. This should mean that the tropical waves coming off of Africa this season will be strong and have the potential to develop into significant hurricanes. A few tropical waves have already exited the coast of Africa – May is typically the start of the “wave train” which usually lasts until November. However, tropical waves do not usually develop much until July or August, and it is highly unlikely that any of the tropical waves this month will develop into tropical cyclones.

Based on recent trends, I forecast that the 2017 Atlantic hurricane season will have roughly 13 named storms, 6 hurricanes and 3 major hurricanes, not including Tropical Storm Arlene which formed in April. This is right around the long-term average for hurricane activity in the Atlantic basin. This forecast takes into account the possibility of the development of El Niño, but could be too low if the ENSO remains neutral or too high if a moderate El Niño forms by the peak of the season. Hurricane season forecasting is very complicated – even the experts cannot exactly predict the activity of the season.

I will release an updated forecast for the Atlantic hurricane season on August 1, and I also plan to release a forecast for the East Pacific hurricane season later this month. During the season, I may also release blogs discussing new model runs.  I’ll be back with another blog tomorrow.

My season probabilities:

• 35% chance of an above-average season (ACE >111) – This will likely occur if ENSO remains neutral throughout the entire season.
• 40% chance of a near-average season (ACE 66-111)
• 25% chance of a below-average season (ACE <66)