Seedlings for Tropical Cyclones

Tropical cyclones don’t develop out of nowhere.  A pre-existing disturbance, such as a tropical wave, is needed.  Tropical waves are generated by instability resulting from the temperature gradient over western and central North Africa due to extremely warm temperatures over the Sahara Desert in contrast with the much cooler temperatures along the Gulf of Guinea coast.  Typically, these tropical waves emerge from the coast of Africa every 3 to 4 days and move westward in the lower tropospheric flow across the tropical Atlantic and Caribbean,  often continuing into the eastern Pacific.   About 60% of Atlantic tropical storms and category 1 and 2 hurricanes develop from tropical waves while about 85% of Atlantic major (category 3, 4 and 5) hurricanes develop from tropical waves.

GOES visible satellite image from 10:45 am EDT July 9, 2010

Today’s satellite imagery shows several thunderstorm clusters associated with tropical waves over the western Caribbean, eastern Caribbean, just east of the Lesser Antilles, midway between Africa and the Caribbean, and just off the coast of Africa.

These tropical waves are currently not showing signs of development likely due to a combination of vertical wind shear between the lower and upper levels of the troposphere and/or somewhat drier air over the tropical Atlantic.  But it is only a matter of time before the atmosphere becomes more conducive for tropical cyclone development.  The warm ocean waters are already in place and the seedling disturbances are becoming more trackable as is typical for this time of year.  The historical record shows that the peak of the Atlantic hurricane season is from the middle of August to the middle to end of October.  We will be there before we know it.


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