Climate of the Philippines

Monsoons are large-scale sea breezes which occur when the temperature on land is significantly warmer or cooler than the temperature of the ocean. Most summer monsoons or southwest monsoons (Filipino: Habagat) have a dominant westerly component and a strong tendency to ascend and produce copious amounts of rain (because of the condensation of water vapor in the rising air). The intensity and duration, however, are not uniform from year to year. Winter monsoons or northeast monsoons (Filipino: Amihan), by contrast, have a dominant easterly component and a strong tendency to diverge, subside and cause drought.

The summer monsoon brings heavy rains to most of the archipelago from May to October. Annual average rainfall ranges from as much as 5,000 millimeters (197 in) in the mountainous east coast section of the country, to less than 1,000 millimeters (39 in) in some of the sheltered valleys. Monsoon rains, although hard and drenching, are not normally associated with high winds and waves.

At least 30 percent of the annual rainfall in the northern Philippines can be traced to tropical cyclones, while the southern islands receiving less than 10 percent of their annual rainfall from tropical cyclones. The wettest known tropical cyclone to impact the archipelago was the July 1911 cyclone, when the total precipitation for Baguio was distributed over the four days as: 14th – 879.8 mm (34.6 in), 15th – 733.6 mm (28.9 in), 16th – 424.9 mm (16.7 in), 17th – 200.4 mm (7.9 in);[3][4] followed by extraordinary drought from October 1911 to May 1912, so that the annual amount of those two years were hardly noticeable.

The Philippines sit across the typhoon belt, making dangerous storms from July through October. Climate change exacerbates the situation with typhoons in the Philippines.[7] Typhoons are especially hazardous for northern and eastern Luzon and the Bicol and Eastern Visayas regions, but Manila gets devastated periodically as well. Bagyo is the Filipino term for any tropical cyclone in the Philippine Islands.[4] From the statistics gathered by PAGASA from 1948 to 2004, around an average of 28 storms and/or typhoons per year enter the PAR (Philippine Area of Responsibility) – the designated area assigned to PAGASA to monitor during weather disturbances. Those that made landfall or crossed the Philippines, the average was nine per year. In 1993, a record 19 typhoons made landfall in the country making it the most in one year. The fewest per year were 4 during the years 1955, 1958, 1992, and 1997.[8]

PAGASA categorises typhoons into five types according to wind speed. Once a tropical cyclone enters the PAR, regardless of strength, it is given a local name for identification purposes by the media, government, and the general public.[9]

There are four recognized climate types in the Philippines, and they are based on the distribution of rainfall (See the Philippine Climate Map at the top).[lower-alpha 1] They are described as follows:[1]

The average year-round temperature measured from all the weather stations in the Philippines, except Baguio, is 26.6 °C (79.9 °F). Cooler days are usually felt in the month of January with temperature averaging at 25.5 °C (77.9 °F) and the warmest days, in the month of May with a mean of 28.3 °C (82.9 °F).[1] Elevation factors significantly in the variation of temperature in the Philippines. In Baguio, with an elevation of 1,500 m (4,900 ft) above sea level, the mean average is 18.3 °C (64.9 °F) or cooler by about 4.3 °C (8 °F). In 1915, a one-year study was conducted by William H. Brown of the Philippine Journal of Science on top of Mount Banahaw at 2,100 m (6,900 ft) elevation. The mean temperature measured was 18.6 °C (65.5 °F), a difference of 10 °C (18 °F) from the lowland mean temperature.[16]

Relative humidity is high in the Philippines. A high amount of moisture or vapor in the air makes hot temperatures feel hotter. This quantity of moisture is due to different factors – the extraordinary evaporation from the seas that surrounds the country on all sides, to the different prevailing winds in the different seasons of the year, and finally, to the abundant rains so common in a tropical country. The first may be considered as general causes of the great humidity, which is generally observed in all the islands throughout the year. The last two may influence the different degree of humidity for the different months of the year and for the different regions of the archipelago.[17]

The climate of the country is divided into two main seasons:

1. the rainy season, from June to the early part of October;
2. the dry season, from the later part of October to May. The dry season may be subdivided further into (a) the cool dry season, from the later part of October to February; and (b) the hot dry season, from March to May.[1] The months of April and May, the hot and dry months when schools are on their long break between academic years, is referred to as summer while in most of the northern hemisphere those months are part of spring.