African dust

[hurricanetrack]

Wow, that's a lot of dust moving west off of Africa. You can really see it well in this sat pic:

http://www.esl.lsu.edu/webpics/goes/Sto ... est_lc.jpg

[Meso]

[cycloneye]

These sal outbreaks mean that the Azores high is fairly strong and it can be transported westward for thousands of miles as the trade winds are moderate to strong.I wonder if these sal big outbreaks continue if it may cause the CV season to not be as active as the sal blocks the sun from the water to not warm them enough.

[MiamiensisWx]

Firstly, the SAL is not dust. The populace continually misrepresents the SAL as strictly dust. It is a stable air mass that often indicates the presence of a subsidence inversion that "caps" convection.

"The Saharan Air Layer (SAL) is an intensely dry, warm and sometimes dust-laden layer of the atmosphere which often overlays the cooler, more-humid surface air of the Atlantic Ocean. In the Sahara Desert region of North Africa, where it originates, it is the prevalent atmosphere, extending from the surface upwards several kilometers. As it drives, or is driven, out over the ocean, it is lifted above the denser marine air. This arrangement is an inversion where the temperature increases with height. The boundary between the SAL and the marine layer suppresses or "caps" any convection originating in the marine layer. Since it is dry air, the lapse rate within the SAL itself is steep, that is, the temperature falls rapidly with height."

http://en.wikipedia.org/wiki/Saharan_Air_Layer

There has been a significant pattern change over the Atlantic basin over the past several weeks, which is largely in response to the North American and Pacific pattern. Amplification and persistence of the strong upper ridge over the Southwest states and the Aleutians has combined with a strongly negative NAO and staunchly supported the continuation of the broad H5 mean trough over the Midwest and eastern CONUS. Consequently, upper divergence/shear vectors have been intense over the Gulf of Mexico and the majority of the Caribbean Sea/southwestern Atlantic, partially because of multiple shortwave impulses. The previously meager Azores ridge has intensified, and we have observed strengthening low-level easterlies (stronger easterly shear) and the re-emergence of a subsidence inversion and stable SAL, which is suppressing the ITCZ slightly further south and inhibiting convection. Overall, the basin looks extremely hostile, and I don't see any changes in the short to medium term. However, this only applies to the rest of this month and early July.

[MiamiensisWx]

Finally, this is exceedingly familiar in June, as the SAL typically peaks at this time. Several conducive factors suggest an active Cape Verde season. Mean SSTA in the MDR remains slightly above average, though some minute cooler areas have appeared. ITCZ will likely lift north when the pattern and global circulation "reloads" again. Below average SLP will also aid cyclogenesis, especially with the trends for greater low level vorticity and convergence associated with several of the systems that have exited the coast throughout the month. I highly doubt the current pattern will "look identical" in August/September.

[KWT]

Should be noted that the Azores high does appear to be fairly strong right now and if anything the models are only strengthening the Azores high over the next week with it peaking probably between 1031-1033mbs. Should drag a lot of stable air and dust off Africa so it shouldn't decrease all that much.

As others have said this is around the time that SAL peaks and probably won't ease down for a little while yet, though by late August we should be seeing a large decrease.

[LarryWx]

Firstly, the SAL is not dust. The populace continually misrepresents the SAL as strictly dust. It is a stable air mass that often indicates the presence of a subsidence inversion that "caps" convection.

While I'm not disagreeing with you, it has been my understanding that the presence of dust, itself, serves to make it even more hostile as per the info at this link:

http://science.nasa.gov/headlines/y2001/ast22may_1.htm

From this link:

"Our laboratory analysis of the desert dust showed that [dust] particles contained very little water-absorbing matter," says co-author Yinon Rudich of the Weizmann Institute. "As a result, even large dust particles form relatively small cloud droplets."

"Dust and other particles in the air cause water droplets in clouds to be smaller, leading to decreased rain."

So, wouldn't a SAL with more dust be more hostile to trop. development than a SAL with little dust? Are SAL and dust, indeed, actually two separate factors that both work to make it more hostile?