UNUSUAL DRY AIR CROSSING ATLANTIC

A large batch of dry air has come off the coast of Africa and is crossing the Atlantic reaching the Lesser Antilles. You can see this by the red and yellow enhancement colors in this graphic from CMISS

What is so unusual is degree of dryness during the month of November. A climatological record of dust events since 1982 shows November being the least frequent month for having these events. June and July is typically a common time of year for dust to be lifted off the desert of western Africa and transported aloft by easterly air currents.

These dust cycles can hold back hurricane development and the events have been tied to coral bleaching and red tide outbreaks in the Gulf of Mexico.

A forecast for the Saharan Dry Air Layer (SAL) for the summer of 2008, predicts fewer outbreaks. This could coincide with our current La Nina situation and result in an active 2008 hurricane season. The method for predicting SAL months in advance is based on the West African cloud cover record this past summer. More clouds would mean higher rainfall in the region. A wetter season would result in fewer dry air outbreaks next year.

A great new tool to spot dry air and moisture in the atmosphere is the MIMIC
graphic above. This product by CIMSS shows the SAL in dark blue moving out into the Atlantic and passing over the Cape Verde Islands and reaching Barbados. I love this tool because it integrates the total amount of water vapor in the atmospheric all the way down to the surface. Conventional satellite based water vapor imagery detects moisture from about 500 mb or around 18,000' and above. Look at how dry Jacksonville is above.