Tropical climates and trade winds
Pressure Zones in the Tropics and Subtropics
Low Pressure Zone
Inter-tropical Convergence zone (ITC)
Also known as Equatorial Trough or doldrums
It is a 10-12º band straddling the equator
It moves with the sun south of 0 in the dry season (Nov-Apr) producing stronger trades for Boracay and dry skies and north of 0 in the wet season (June-Sept) bringing lighter wetter winds.
This is an area of low pressure because of the intensity of solar radiation which heats the air
High Pressure Zone
A band about 30º north and south.
This area is known as the Horse Latitudes, characterized by calm and unstable, unsteady winds.
In the days of sailing ships, horses got sick at this point and were often thrown overboard.
Trade Winds
Dependable winds moving from high pressure zone of horse l
atitudes to the edge of the ITC.
They veer to the west because of the rotation of the earth, thus are easterly winds.
The trade winds dominate the tropics.
Winds blow 10-15 miles per hour, fairly steady 10 to 12ºN & 25ºS. Boracay sits 11.9N therefore perfectly placed for the NE trade winds.
Monsoon winds
Monsoon winds reverse themselves seasonally.
They are best developed in Western parts of oceans or eastern parts of continents, particularly Asia.
Monsoon is based on differential thermal heating and cooling of land areas creating zones of high and low pressure over land in differnet seasons.
Monsoon represents a great break in the general circulation of the atmosphere.
Therefore the Philippines sits in a roaring trade wind zone with monsoonal effects.