A Quiet Hurricane Season in the Atlantic?

The official start of the hurricane season in the North Atlantic was June 1 and most experts are predicting a relatively quiet season, pointing to relatively cool water temperatures in place and a developing El Nino in the Pacific.   El Nino can be thought of as a substantial warming of ocean water in the central and/or eastern Pacific which in turn alters global weather patterns.  Atlantic hurricanes typically encounter more hostile atmospheric conditions during El Nino events, limiting their potential to develop and strengthen.  Most of the inactive seasons in the Atlantic over the past 20 years have occurred during El Nino events.

Where did the tropical cyclones go this season?

In short – the western Pacific.

The Atlantic Basin was predicted by many to have an active season. But the season ended November 30th, and it was a very quiet one. There were 13 named storms in the Atlantic, of which two developed into hurricanes.  The Accumulated Cyclone Energy (ACE) Index is used by the National Oceanic and Atmospheric Administration (NOAA) to measure the severity of hurricane seasons.  It considers the intensity and the lifespan of storms.  The 2013 Atlantic season was well below normal; the ACE index came in at 33, about 31% of the 1981-2010 average of 104.

Super Typhoon Dale (1996) was one of our featured storms on Cyclone Center this year.

On the other side of the planet, in comparison to the Atlantic Basin, the western Pacific appears to be the ‘hot spot’ this season for strong tropical cyclones. The western Pacific has seen 31 storms, 13 being typhoons (in this region, hurricanes are called typhoons). This makes the western Pacific season slightly above the 1981-2010 average of 26 named storms. The ACE index for the Western Pacific, however,  stands at 268.3 – about 88% of the 1981-2010 average of 302.

Typhoons such as Lekima, Usagi, Fransico and of course Super Typhoon Haiyan(Yolanda) will be recorded in the 2013 history book.  A super typhoon is a typhoon whose winds exceed 150 mph, equivalent to a Category 4 or 5 hurricane on the Saffir-Simpson scale.

What has contributed to the strong activity seen in the western Pacific this season? A combination of the right ingredients is the answer. A tropical cyclone needs favorable conditions, such as moisture, warm sea surface temperatures, and lack of wind shear in the upper atmosphere in order to aid development. Based on the activity in the western Pacific, it is likely that those conditions were present much of the season.

The 2013 tropical cyclone season was bittersweet for many; those in the Atlantic were glad for a quiet season while many in the western Pacific were forced to make preparations all season. Our prayers are with those affected by these forces of nature.

Visit Cyclone Center to classify many storms including those past storms that formed in the western Pacific, such as: Supertyphoon Dale (1996), Super Typhoon Herb (1996), Typhoon Faxai (2001), Super Typhoon Mike(1990) and more.

– Davanna G. Saunders is an undergraduate student in Atmospheric Sciences at the University of North Carolina at Asheville.  She recently joined the Cyclone Center team as a classifier and contributor to our social media.

Seasonal Tropical Cyclone Forecasts Are Coming In – But Are They Worth It?

Citizen scientists working on Cyclone Center are working with a few thousand tropical cyclones which have developed since 1978.  Beginning just a few years later, Dr. Bill Gray at Colorado State University (CSU) first began issuing forecasts for the number of tropical cyclones that will develop in the Atlantic Ocean for the upcoming Atlantic season (June 1 – November 30 each year).  Since that time, several other groups, including the U.S. National Oceanic and Atmospheric Administration (NOAA), have also developed similar techniques to predict seasonal activity.  With the official start of the Atlantic season just a couple of weeks away, this year’s predictions are in.

Hurricane Andrew, a devastating Category-5 storm, occurred during an extremely quiet Atlantic hurricane season.

The CSU forecast, issued in April of this year,  predicts 18 named storms (those achieving at least Tropical Storm strength), 9 hurricanes, and 4 major hurricanes (Saffir-Simpson Category 3 or higher).  This is well above the long-term average for the Atlantic.  The NOAA forecast, which relies on similar parameters to predict activity (e.g. warm ocean temperatures, El Nino phase),  puts the chances of an active season at 70%.  Groups in other parts of the world also produce seasonal forecasts for their own region.  For example, the Bureau of Meteorology in Australia issues a national as well as regional seasonal outlooks.   Recently, other groups such as the United Kingdom Met Office have begun issuing “dynamical” forecasts, which explicitly count tropical cyclone-like features in weather models rather than relating environmental conditions to past activity.

Seasonal forecasts receive quite a bit of publicity, despite questions about their skill and usefulness.    Statistical schemes such as the CSU forecast, rely on past connections between environmental factors and TC activity.  They fail especially in predicting extreme seasons, such as the 1995 or 2005 Atlantic seasons, because the models just don’t know about hyperactive years like that.   Dynamical predictions, which theoretically can predict record breaking years since they do not rely on past seasons, have been shown to have better predictive skill than statistical techniques for seasonal TC prediction.

But even if a model were 100% accurate, would it really make a difference?  The majority of systems that do develop into tropical cyclones do not affect land.  Predictions of landfall are made by several groups but have not shown any skill so far.  For any given location of coastline, the chances of a TC impact in any given year are very small.  So if a homeowner hears that the upcoming season will be active, should any action be taken?  Does it really matter if we’re going to get 12 storms this year or 11?  Remember that some of the most devastating hurricane events in U.S. history, such as Andrew in 1992,, occurred during inactive seasons.  In the end, how do seasonal forecasts help society?

One could argue that any publicity that gets people to assess their readiness is good – but I think that most will not do anything.   Perhaps more effort should be invested in determining how the nature of tropical cyclones will change in our warming world.  Cyclone Center is going to provide researchers with new data that will help determine if and by how much the nature of global tropical cyclone activity has been recently changing.  With stronger tropical cyclones predicted in the Atlantic and other parts of the world – along with rising sea levels – time and energy is better spent developing plans for mitigation for the big ones rather than issuing forecasts with little or no value for coastal residents.

– Chris Hennon is part of the Cyclone Center Science Team and Associate Professor of Atmospheric Sciences at the University of North Carolina at Asheville