Major hot deserts in northern hemisphere are located between 20-30 deg N latitudes and on the western side of the continents. Why?

The great hot deserts — the Sahara, Arabian, Thar, and the Sonoran-Mojave of North America — cluster between 20 and 30 degrees N on the western sides of continents. This location is a product of the general circulation of the atmosphere reinforced by oceanic and relief factors.

Why between 20-30 degrees N

• This belt lies under the subtropical high pressure cells, the descending limb of the Hadley cell. Subsiding air warms adiabatically, its relative humidity falls, and stable anticyclonic conditions prevent cloud formation and rainfall.
• The belt is also the zone of divergence from which trade winds blow away, so moisture-bearing convergence is absent for most of the year.

Why on the western margins

• The north-east trade winds are offshore on western margins: having crossed the continent, they arrive dry, while the eastern margins receive the same trades as moist onshore winds (hence wetter eastern coasts).
• Cold ocean currents — the Canaries off the Sahara and the California current off Mexico — chill the surface air, increase stability and produce advection fog rather than rain, intensifying coastal aridity (a mechanism at its extreme in the Atacama with the Peruvian current).
• Rain-shadow and continentality reinforce dryness where highlands intercept any residual moisture, as the Rockies do for the interior south-west of the USA.

Thus subsiding subtropical air, offshore trades and cold currents combine to make the 20-30 degrees N western margins the driest parts of the northern hemisphere.