Philippine Monsoon Seasons
Beyond individual typhoons, the Philippine year is governed by two monsoons: the wet habagat and the drier amihan. Understanding them explains when the floods come.
Two monsoons, one tropical climate
The Philippines is hot and humid year-round, but the prevailing wind reverses with the seasons, switching the country between a wet phase and a relatively drier one — with transition periods in between.
Habagat — the southwest monsoon (roughly June to September)
Warm, moisture-laden winds blow from the southwest, bringing the heaviest rains of the year to the western Philippines, including Metro Manila. Habagat rain can be torrential and prolonged, and it is frequently enhanced by nearby typhoons even when the storm itself does not make landfall — the mechanism behind several of Manila's worst floods. This is the classic wet season for the western side of the archipelago.
Amihan — the northeast monsoon (roughly October to March)
Cool, drier winds flow from the northeast. This brings more comfortable, less humid weather to much of Luzon and the western Philippines, but it delivers rain to the eastern seaboard, which faces the incoming winds. Amihan is generally the more pleasant season for Manila and the west.
The transition periods
Between the monsoons, winds go light and variable and afternoon thunderstorms become common, sometimes producing the small tornadoes and waterspouts known as buhawi.
How the monsoons drive flooding
The habagat is the flood-maker. When its moisture is focused over Luzon — especially with a typhoon offshore drawing the flow in — rainfall totals can overwhelm rivers and drainage in hours. Tropical Storm Ketsana (Ondoy) in 2009 famously combined with the monsoon to inundate Metro Manila. See flooding in the Philippines for more.