Outlook for the hurricane season in the Atlantic

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  • Eye of the hurricane Sandy over New York in 2012

    Sea-surface temperature anomalies in the Atlantic Basin in late March 2015 compared to 1980-2010 average. Blue/purple colors denote cooler than average SSTs. Yellow/orange/red colors denote warmer than average SSTs. (Klotzbach and Gray April 2015 hurricane season forecast).

    NOAA/NESDIS: Sea Surface Temperature (SST) Anomaly in the Pacific shows warmer than usual SSTs, that is called El Niño conditions (16th/04/2015).

  • Outlook for the hurricane season in the Atlantic
    19.04.2015 14:57

    The 2015 Atlantic hurricane season will have its official start on June 1st and it will last until November 30th. Many people live around the Gulf of Mexico or go to the Caribbean to enjoy their holidays during these months and many forecasters have already embarked to Mexico and Caribbean on preparedness missions. So, let’s take a look at the early outlook for this season.

    The Colorado State University (CSU) has released its outlook at the beginning of April and it forecasts one of the least active in decades. According to this estimate, there could be seven named storms and three hurricanes. Just one is projected to attain major hurricane status. These numbers are well below the 30-year average of 12 named storms, six hurricanes, and three major hurricanes.

    Long-range hurricane forecasts of this nature are notoriously difficult and have limited success. It is likely that there are factors which cannot yet be keyed into these predictions.

    Nevertheless the CSU researchers have based the outlook on a combination of 29 years of statistical predictions combined with analogous seasons exhibit similar features of sea-level pressure and sea surface temperatures in the Atlantic and eastern Pacific Oceans. The fact that there will be less activity than usual does not mean that a hurricane has less chance of making landfall or passing through some islands. There will be a risk of damaging winds and torrential downpours, anyway.

    Why does CSU think that hurricane activity in 2015 is going to be subdued?

    First of all, for a hurricane to form it needs, among other ingredients, a sea surface temperature (SST) of more than 26ºC to fuel a hurricane with water vapour. Tropical and sub-tropical waters reach this level of warmth every year but the ocean from the Windward Islands eastwards to the west African coast, where hurricanes spawn, is a little cooler than normal.

    A hurricane may form in any case in the western Atlantic Basin or Gulf of Mexico given that SSTs will easily top 26C but there is a narrower space to form and develop.

    Most importantly, though, El Niño is going to strengthen (anomalous warming of eastern Pacific waters) and this is known to have a tendency to subdue hurricane formation because it produces greater wind shear over the Atlantic than normal

    The general rule is:

    - Warming in the eastern equatorial Pacific: lower number of Atlantic tropical cyclones.
    - Warming in the central equatorial Pacific: higher number of Atlantic tropical cyclones

    Is there any influence by global warming on hurricane
    s?

    For statistical reasons, a single hurricane event cannot be attributed to climate variations of any kind, but what can we say about the effects of climate change on tropical cyclones? Should there is a less active season than of late, does it mean that the ongoing climate change is no longer influencing hurricanes?

    There is a strengthening consensus that the frequency of high category tropical cyclones should increase as the planet warms. Basic theory and a variety of numerical simulations support this, as well as the projection that tropical cyclones should produce substantially more rain, owing to the increased moisture content of the tropical atmosphere. The latest research on hurricanes and global warming indicates that the inner core dimensions of a hurricane should increase over time. That means a higher diameter on hurricanes and consequently more destructive potential.

    Obviously, a single event or an entire hurricane season – either more or less active than normal - does not say anything about a long-tern global climate trend.  If we look at the overall pattern we have seen destructive and intense cyclones in the western Pacific, such as typhoons Haiyan and Pam while, perhaps this season is quiet in the Atlantic.

    Despite the above outlook, both for residents and people thinking to holiday near the Gulf of Mexico, it is important to keep an eye on the useful forecast provided by the National Hurricane Center (NHC) or our website and be ready in case one of these events comes to you. A season can deliver many storms but have little impact, or deliver few storms and have one or more hitting the place where you are.

    Mario Cuellar and Stephen Davenport