Breaking down hurricane season 2013

So far this hurricane season, we have had a total 6 named storms in the Atlantic Basin.  Only one made landfall in the United States (Andrea) (Figure 1), while two made landfall in Mexico or Latin America (Barry and Fernand).  No hurricanes have formed and based on the forecast, no hurricanes will form until AT LEAST the first week of September.  Since 1983, there have only been four other seasons in which the first hurricane was recorded after September 1st.  The last being 2002.

So why the slow start to this season?  Not that we are complaining, but lets break it down a little bit more.  Earlier this year, Dr. Gray and his team of experts at Colorado State University forecasted an active season with 18 named storms of which 9 would become hurricanes with 4 major hurricanes.

The active forecast was a based on two very important factors: the El Nino phenomena (or lack there of) and warmer than normal sea surface temperatures in the main development area.  Of course I'm just keeping it simple here; addition variables were considered, but it's still very difficult to forecast an entire hurricane season based solely on climatological averages.

At this point we are 12 named storms behind the original forecast.  Keep in mind, the preseason forecast never said we would only have so many storms by this point; it just covered the entire season.  Hurricane season continues through November, and more importantly, September is considered the peak month for hurricane activity.  The last three hurricanes to strike Southeast Texas (Rita, Humberto, and Ike) all struck in September.  Since 1900, 10 hurricanes made direct landfall in Texas during the month of September.  A few more have made landfall near the Texas state line, including Rita in 2005.  In October, a total of 4 named storms have made landfall in Texas during that same 113 year time frame.

So far this year, storms have been struggling to develop because of factors not considered in the preseason forecast.  In the main development zone of the Atlantic Ocean, dust and dry air from the African continent has been choking off tropical systems before they fully develop (Figure 2,3).  

In the Gulf, wind shear as a result of day to day weather patterns has helped to protrude any significant development.

Let's not be too hasty here, the overall pattern is changing!  Weaker trade winds over the Atlantic have reduced the amount of dust coming off the African continent (Figure 4).  That should also translate to lower shear over the Atlantic Ocean and Gulf of Mexico.  Less dust and lower shear means more favorable conditions for tropical development. 

Now in retrospect, 2013 has been a little quieter than our past active seasons, but with September right around the corner, we can't let our guard down.  A pattern change most certainly could open the door to a burst of tropical activity.


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