Why is the South Texas coast so dry?

[Yn0hTnA]

Originally Posted by Westerner92

Much of the world's arid climates are concentrated near the 30*N latitude where high pressure zones are caused by sinking tropical air. The American Southwest, The Sahara, and the Middle East are affected by this.



The humidity of the American South is an anomaly of sorts, then, because the humid air flowing northward from the Gulf combines with the cold lows coming from polar areas. The humid air tends fo flow parallel to the shore rather than on shore in South Texas, and the low pressure areas rarely get that far south. South Texas is following the pattern, with its weather often being dictated by the dry, high-pressure zones putting a cap on storm development.

True, but the South Texas coastal areas in question are well below 30N in latitude; Brownsville, TX, for instance, is around 25N. Houston is far closer to the 30N high-pressure zone than Brownsville is, and yet it consistently gets more rainfall per year than Brownsville (nearly 30 inches more), in both summer and winter.

And I don't think the South's humidity is an anomaly; the South is on the eastern coast of a continental landmass at 30N; areas of the world in that circumstance break the arid climate regime, since they are on the western side of the high, where it is able to move in moist, humid air poleward. Eastern Asia countries like China, and Japan exhibit the same humid subtropical climate as the South, and at the same latitudes as well.

Subtropical ridge - Wikipedia, the free encyclopedia

Originally Posted by rynetwo

People are also leaving out the Mexican Plateau to west. Warm dry air flows over this large plateau and creates a cap of warm air aloft over most of South Texas. As mentioned before low pressure systems rarely make it that far south and thus that cap or air cannot be broken.



NOAA's National Weather Service - Glossary

Perhaps this is the true reason.

[Westerner92]

Originally Posted by Yn0hTnA

True, but the South Texas coastal areas in question are well below 30N in latitude; Brownsville, TX, for instance, is around 25N. Houston is far closer to the 30N high-pressure zone than Brownsville is, and yet it consistently gets more rainfall per year than Brownsville (nearly 30 inches more), in both summer and winter.

When talking about climatic zones on a global scale, 5* of latitude is almost negligible since we're talking in generalities. The Sahara and Arabia are concentrated in the 20s N latitudes, but they epitomize effects of the subtropical highs that I described. The American South and southern China are anomalies when you consider that the majority of the 30*N line traverses desert.