Monsoons are seasonal winds that bring heavy rains.
According to the Philippine Atmospheric Geophysical and Astronomical Services Administration,
the country experiences two kinds of monsoons—the northeast monsoon and the southwest
monsoon.
A monsoon is a seasonal change in the direction of the prevailing, or strongest, winds of a region.
Monsoons cause wet and dry seasons throughout much of the tropics. Monsoons are most often
associated with the Indian Ocean.
Monsoons always blow from cold to warm regions. The summer monsoon and the winter
monsoon determine the climate for most of India and Southeast Asia.
It has a different name in each country that it affects. In the Philippines, the Summer
Monsoon (West or southwest winds) is called the Habagat (ha-bag-at) and the Winter Monsoon
(North or northeast winds) is called the Amihan (a-me-han).
Summer Southwest Monsoon - Habagat
Summer Monsoon weather is characterized by a strong, generally West or southwest
breeze that is responsible for bringing significant rainfall to the Asian subcontinent and to South and
East Asia. The significant southwest monsoon rainfall is a by-product of air passing over large areas of
warm equatorial ocean, stimulating increased levels of evaporation from the ocean’s surface; the
southwest monsoon air, now laden with water vapour, cools as it moves north and as it rises over
land; at some point the air is no longer able retain its moisture and precipitates copious volumes to
irrigate rice fields and drench rainforests, sometimes causing severe flooding below hillsides that have
been foolishly stripped of forest cover by Man. The Summer Monsoon (West or southwest) is the
predominant weather pattern throughout most Asian tropical destinations from late April through to
early October each year.
The southwest monsoon is called habagat. Characterized by heavy rains that last
for a week, it affects the country from July to September and brings the rainy season to
the western part of the country.
Winter Northeast Monsoon - Amihan
Winter Monsoon weather features a generally less strong, East or northeast breeze that is
cooler and drier (compared to the Summer Monsoon weather), with prolonged periods of successive
cloudless days. The Winter Monsoon (North or northeast winds) features cool and dry air that
originates in a vast anticyclone - a weather system with a high barometric pressure - which forms over
Siberia, Mongolia and northern China during each northern winter. The Winter Monsoon air from the
anticyclone pushes outward in a clockwise motion from its center and competes with the Summer
Monsoon over a period of a week or two, usually starting in late September and early October, before
finally dominating the weather with a cooler and drier northeast monsoon in most Asian tropical and
sub-tropical destinations through to the following April.
The northeast monsoon, commonly called amihan, affects eastern Philippines
from October to late March. Initially a cold, dry air mass, it comes from Siberia and
gathers moisture over the Pacific Ocean before reaching the eastern parts of the
country. It is characterized by widespread cloudiness with rains and showers.
The Inter Tropical Convergence Zone (ITCZ)
Many people who listen to weather forecasts are confused about the inter tropical
convergence zone. The Inter Tropical Convergence Zone, or ITCZ, is a belt of low pressure which
circles the Earth generally near the equator where the trade winds of the Northern and Southern
Hemispheres come together. It is characterized by convective activity which generates often vigorous
thunderstorms over large areas. But it is easy to understand it once you know that warm air rises, and
air moves toward the place where warm air is rising.
The inter tropical convergence zone is the place where winds in the tropics meet or converge . (Recall
that the area near the equator is called the tropics.) In time the rising warm air will form clouds, which
may lead to thunderstorms. Now you know why weather forecasters often blame the ITCZ for some
heavy afternoon rains. The band of white clouds in the following picture shows the location of the
ITCZ.
