2013 Atlantic Hurricane Season

Fortunately for many along the Atlantic Coastline the 2013 Hurricane Season has been relatively slow.  As of August 28th there have been 6 Named Storms in the Atlantic Basin.  All have been Tropical Storms, weak and questionable tropical storms.  Andrea was arguably a weak “subtropical storm”, probably not a true tropical storm.  Juston and I chased Andrea as it passed over Florida and Georgia in June and found it difficult to find a breeze in the core rain bands as the storm came onshore. We documented a tornado from a supercell in a band moving over Southeast Georgia far from the core of the system, but from our observations and analysis of the available data it appeared Andrea was most likely subtropical.

Barry, Chantal, and Dorian were barely tropical depressions and it would be easy to argue whether they reached Tropical Storm strength.  Erin and Dorian briefly had more robust appearances on satellite, but only enough to maybe estimate them to have briefly attained minimum tropical storm status.  Fernand developed quickly from a cluster of thunderstorms in the Bay of Campeche, but it’s difficult to say whether it was able to intensify into a tropical storm before it moved over the Mexican Coast.  With exception of Andrea (most likely subtropical) all the 2013 Named Storms were barely on the threshold of Tropical Storm status and perished quickly due to high wind shear, dry air, land, or all three.

Below are a few satellite images of some of 2013 tropical systems:

Satellite image of T.S. Andrea more indicative of a subtropical storm

Satellite image of T.S. Andrea more indicative of a subtropical storm

Dry air, wind shear, & land made organizing difficult for T.S. Barry

Dry air, wind shear, & land made organizing difficult for T.S. Barry

Dry air & wind shear obliterated T.S. Chantal's updrafts

Dry air & wind shear obliterated T.S. Chantal’s updrafts

T.S. Dorian didn't stand a chance against dry air & high wind shear

T.S. Dorian didn’t stand a chance against dry air & high wind shear

So far the Atlantic Basin has remained mostly unfavorable for the development of Tropical Cyclones.  Large areas of high wind shear has ripped apart many possible tropical systems this summer.  A Tropical Cyclone is vertically stacked, meaning the system is very similar from the surface to thousands of feet up into the mid-levels of the atmosphere. Wind shear can offset the vertical balance of a tropical cyclone causing it to weaken or dissipate.

Large swaths of deep dry air masses have been evaporating storms.  Individual storm updrafts need moisture and heat to strengthen and propagate.  Tropical cyclones are comprised of a vast amount of individual storm updrafts generating an incredible amount of heat (from latent heat release as water vapor condenses into cloud water droplets in storm updrafts).  This heat generates the low pressure at the center of a tropical cyclone.  Large quantities of dry air can evaporate storm updrafts, which causes evaporational cooling as cloud droplets become water vapor again.  This cooling combined with the loss of storm updrafts can weaken or kill a tropical cyclone.  Large-scale global sinking motion affecting the Atlantic Basin has created dry air masses, and large dry dust storms blowing off of Western Saharan Africa has, also, contributed to the dry Atlantic air.

The 2013 Atlantic Hurricane Season is still young and the sea surface temperatures are very warm.  Plenty of time and energy to generate an active Hurricane Season and it only takes one strong cyclone making landfall to cause a major disaster.  People living along the Atlantic Coast should to utilize these “quiet days” to prepare, create or revisit a hurricane disaster plan.

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