Map from Google - Philippines

In the Philippines, an archipelago of thousands of islands, the climate is generally tropical maritime, with a relatively cool season from December to February, when the north-east trade winds prevail, and a hot, humid and rainy season from May to November, in which the south-west monsoon prevails. Between March and May, before the arrival of the summer monsoon, the temperature increases and reaches the highest levels of the year, especially in the centre-north and the interior of the larger islands: hence, in general the coolest month (or the least hot) is January, while the warmest is May.
In the north of Luzon, from December to March cool air masses can sometimes arrive, so much so that at night the temperature can drop to around 12/15 °C (54/59 °F). In the southern islands, close to the Equator, the temperatures are more stable, and remain high all year round.
Even relative humidity in the Philippines is almost always high, and makes the heat muggy, at least in the plains.
Some areas (usually the eastern coast, facing the Philippine Sea), have an equatorial climate, ie rainy throughout the year. In fact, during winter the northeast trade winds discharge a large amount of moisture in the form of rain on exposed coasts and slopes. This in general rarely happens in the inner islands, which are more sheltered, and even less along the western slopes, where winter is a dry season.
The tropical rains typically occur in the form of downpour or thunderstorm in the afternoon, except during tropical storms and typhoons, which can last for a few days and are accompanied by strong winds.

Equatorial climate

Philippines - area with an equatorial climate

In summer it rains all over the Philippines; the equatorial climate zones are those in which it rains even in winter, that is, those exposed to the northeast winds. They are the eastern part of the island of Luzon, some of the Eastern Visayas, like the island of Samar and the eastern part of Leyte, the north-east of Mindanao and the smaller southern islands. In these areas, more than 100 millimetres (4 inches) of rain per month fall even in winter, which is often the rainiest season. In fact these areas, being exposed to the easterly winds, are generally at least partially sheltered from the summer monsoon, which as mentioned blows from the south-west. In these areas the annual precipitation exceeds 2,500 mm (98 in), but in most of the easternmost coast it exceeds 3,000 mm (118 in), and in some cases even 4.000 mm (157 in).
Here is the average precipitation in Legazpi, located in the south-east of the island of Luzon.
Average precipitation - Legazpi
LegazpiJanFebMarAprMayJunJulAugSepOctNovDecYear
LegazpiJFMAMJJASONDY
Prec. (mm)2951951951501802402401802152654854603100
Prec.(in)11.67.77.75.97.19.49.47.18.510.419.118.1122
Days191515151416171617202222208

Here are the average temperatures in Legazpi.
Average temperatures - Legazpi
LegazpiJanFebMarAprMayJunJulAugSepOctNovDec
LegazpiJFMAMJJASOND
Min (°C)222223242525242424242424
Max (°C)292930313232323232313029
Min (°F)727273757777757575757575
Max (°F)848486889090909090888684

Being rainy throughout the year, these areas of the Philippines honestly do not have a beautiful climate, and not surprisingly here you won't find large cities.
The least rainy period varies depending on area, and advances in the year proceeding from north to south. In Legazpi (Luzon Island), less than 200 mm (8 in) per month fall from March to May, while in Borongan (Samar island) this happens from July to September.
The southernmost islands (Basilan, Sulu, Tawi-Tawi), which lie north of Borneo, must be put into the equatorial climate zone, with rainfall even in winter, but since they do not have an evident peak in this season, they can be visited from February to April, and after all even from June to September, when however it rains on average every two days.
Here is the average precipitation of Bongao, in the province of Tawi-Tawi.
Average precipitation - Bongao
BongaoJanFebMarAprMayJunJulAugSepOctNovDecYear
BongaoJFMAMJJASONDY
Prec. (mm)2101751351502101901701451502152002102160
Prec.(in)8.36.95.35.98.37.56.75.75.98.57.98.385
Days141111101316151515171616169

Tropical climate

Philippines - areas with a tropical climate

In the rest of the Philippines, the climate can be defined as tropical, since it is possible to identify a dry season, which coincides with winter, and is most evident in the western part (blue area), and less evident, but still present, in the central part (green area), while the summer monsoon is generally more intense in the western part.
In this area, the biggest cities of the Philippines are found, starting from the capital Manila.
In the northernmost islands (Batanes and Babuyan), which are in the intermediate area circled in green, it's pretty cool from December to February, with average highs around 24/25 °C (75/77 °F), because they are located far to the north, almost at the Tropic, and are affected by cool air masses from the Asian continent.
Here are the average temperatures of Santo Domingo de Basco, in the Batanes province, in the far north of the Philippines.
Average temperatures - Basco
BascoJanFebMarAprMayJunJulAugSepOctNovDec
BascoJFMAMJJASOND
Min (°C)192021232525252524232221
Max (°C)242527283131313130282725
Min (°F)666870737777777775737270
Max (°F)757781828888888886828177

The wettest period is from July to December, but even January is often very rainy, in fact in this month the rains in some places still amount to 180 mm (7 in). It goes a bit better in February, but the driest months here are March and April, so they will be the ones to be preferred for a visit.
Here is the average precipitation in Basco.
Average precipitation - Basco
BascoJanFebMarAprMayJunJulAugSepOctNovDecYear
BascoJFMAMJJASONDY
Prec. (mm)18012590701702602804203803302952552850
Prec.(in)7.14.93.52.86.710.21116.5151311.610112.2
Days18141081014152018181919183

In winter, the sea remains warm enough for swimming even in this northernmost part of the Philippines, although as we said the air can be a bit cool.
Sea temperature - Basco
BascoJanFebMarAprMayJunJulAugSepOctNovDec
BascoJFMAMJJASOND
Sea (°C)252526272829292929282726
Sea (°F)777779818284848484828179

In the interior of Luzon, the pre-monsoon heating from March to May is fairly noticeable: there are hot cities like Angeles, San Fernando, Tarlac, Cabanatuan and Tuguegarao, which in this period easily reach 35/37 °C (95/99 °F), but with peaks of 40 °C (104 °F).
Here are the average temperatures in San Fernando.
Average temperatures - San Fernando
San FernandoJanFebMarAprMayJunJulAugSepOctNovDec
San FernandoJFMAMJJASOND
Min (°C)202022232323232323232221
Max (°C)313234353534323232323231
Min (°F)686872737373737373737270
Max (°F)889093959593909090909088

The metropolitan area of Manila and Quezon City is located in a better position, because it is situated on the coast and therefore gets some breezes, however, being a big city, the so-called urban heat island effect is evident. In Manila and Quezon City, it's hot all year round, since the maximum temperature is around 30 °C (86 °F) even in winter. Here are the average temperatures.
Average temperatures - Manila
ManilaJanFebMarAprMayJunJulAugSepOctNovDec
ManilaJFMAMJJASOND
Min (°C)242425262726262626262524
Max (°C)303132343332313131313130
Min (°F)757577798179797979797775
Max (°F)868890939190888888888886

The dry season, from January to April, is very pronounced: in general, it almost never rains, especially in February and March, which are the driest months. The hottest months are April and May, in which the average maximum temperature is around 33/34 °C (91/93 °F) during the day, with peaks of 36/38 °C (97/100 °F). In fact, high temperatures like these are possible even in the rainy season, albeit more rarely. During the rainy season, from June to October, the average temperature drops, so that highs are around 31/32 °C (88/90 °F), although night temperatures remain high, around 26 °C (79 °F) and the humidity makes the heat muggy. The rainiest months is August, with about 475 mm (18.5 in) on average. Here is the average precipitation.
Average precipitation - Manila
ManilaJanFebMarAprMayJunJulAugSepOctNovDecYear
ManilaJFMAMJJASONDY
Prec. (mm)1572020140285365475335200110552025
Prec.(in)0.60.30.80.85.511.214.418.713.27.94.32.279.7
Days4233101622222018149143

The amount of sunshine is never scarce even in the wettest months, because usually in the morning the weather is good, while in the afternoon or in the evening, showers and thunderstorms often occur.
The best months to visit Manila are January and February, being the least hot among those of the dry period.
At Manila, the sea is warm all year round, with little variation over the months, and this applies also to the rest of the country.
Sea temperature - Manila
ManilaJanFebMarAprMayJunJulAugSepOctNovDec
ManilaJFMAMJJASOND
Sea (°C)272728293030302929292928
Sea (°F)818182848686868484848482

Manila

Cebu City is located in the group of the central islands (Visayas), which are more sheltered, so they are moderately rainy but without excesses. Here, about 1,350 mm (53 in) of rain per year fall, of which less than 100 mm (4 in) from February to May, and a peak of 200 mm (8 in) in October, which is the rainiest month. For many months of the year, it rains on average every second day, except during the period from February to May. We are in the intermediate zone (green), where the dry winter period is present but less pronounced, January is still a pretty rainy month, and therefore the best period is from February to April. Here is the average precipitation.
Average precipitation - Cebu
CebuJanFebMarAprMayJunJulAugSepOctNovDecYear
CebuJFMAMJJASONDY
Prec. (mm)110702030701701801101602001101101340
Prec.(in)4.32.80.81.22.86.77.14.36.37.94.34.352.8
Days14996813151314151214142

Temperatures are high throughout the year, with a hotter period from March to May. Here are the average temperatures.
Average temperatures - Cebu
CebuJanFebMarAprMayJunJulAugSepOctNovDec
CebuJFMAMJJASOND
Min (°C)232323242524242424242423
Max (°C)303032333332323232323131
Min (°F)737373757775757575757573
Max (°F)868690919190909090908888

Davao City is located in the south of Mindanao, overlooking the gulf of the same name, and a short distance from mountains such as Apo and Leonard Kniaseff. Here we are at the boundary between the tropical and the equatorial climate zone; annual rainfall amounts to 2,000 mm (80 in), without there being a well-defined dry season, although between December and March, precipitation drops to around 90/115 mm (3.5/4.5 in) per month.
The least rainy area of the Philippines is the protected Sarangani Bay, in the far south of Mindanao. In General Santos, 1,000 mm (40 in) of rain per year fall, of which about 100 mm (4 in) per month, therefore not very much, in the summer months.

Mountains, typhoons, El Niño

In the Philippines there are many mountains and volcanoes, the highest of which is the aforementioned Mount Apo, in Mindanao, almost 3,000 metres (9,800 ft) high. Along the mountain slopes, usually the rains are more abundant than in the plains, and as mentioned, on the slopes exposed to the wind, showers and thunderstorms are possible throughout the year.
In Baguio, at 1,500 metres (5,000 feet) above sea level, on the island of Luzon, 4,100 mm (160 in) of rain per year fall; the rains are plentiful especially in July and August, with almost one metre (3.3 feet) of rain per month! Here is the average precipitation.
Average precipitation - Baguio
BaguioJanFebMarAprMayJunJulAugSepOctNovDecYear
BaguioJFMAMJJASONDY
Prec. (mm)202050120350420920995650360160554120
Prec.(in)0.80.824.713.816.536.239.225.614.26.32.2162.2
Days44610202327272519106181

However, there is little rain from December to March, and having a mild climate thanks to the altitude, Baguio is a haven to escape the heat of the cities of the plains, especially in the hottest period of the year, ie in March and April, before the rainy season (which here begins already in May).
Average temperatures - Baguio
BaguioJanFebMarAprMayJunJulAugSepOctNovDec
BaguioJFMAMJJASOND
Min (°C)121314151616151515151513
Max (°C)222224252423212121222323
Min (°F)545557596161595959595955
Max (°F)727275777573707070727373

The Philippines are struck in full force by tropical cyclones, which in south-east Asia are called typhoons. The only area which generally remains outside of their trajectory is the southernmost one, therefore the island of Mindanao, especially in the south-central part, and the small southern islands. The typhoon season runs from mid-May to mid-November, although they are more frequent between August and October. However, they can sometimes arrive late, as happened with typhoon Bopha, which affected the Philippines on early December 2012, or with Hagupit, which struck the islands around December 10, 2014.

The Philippines are also affected by the phenomenon known as El Niño, which in some years upsets the climate of large areas of the world, and in the Philippines brings heat, drought and fewer typhoons than usual, while the opposite phenomenon, La Niña, brings heavier rainfall than normal and slightly lower temperatures.

When to go

The best time to visit the Philippines as a whole runs from February to April, because in the regions with an equatorial climate, which in any case are rainy all year round, January is a particularly rainy month. Since March and April are very hot months, February is the best month of all. In areas with a tropical climate, where the winter drought is evident, such as Manila, January is also a good month, and is often the best, because it is dry and also the least hot.
Wanting to travel in July or August, you will prefer Mindanao and the southernmost islands (Basilan, Sulu, Tawitawi), which are less rainy and therefore are acceptable even in this period, and above all are generally sheltered from typhoons.
As mentioned, the sea is warm enough for swimming all year round.

What to pack

In winter: in the northernmost islands (Batanes and Babuyan): spring/autumn clothes, light for the day, sweatshirt or sweater, jacket, raincoat or umbrella. In the north of Luzon, light clothing, a sweatshirt or sweater for the evening, raincoat or umbrella. In Manila and the rest of the Philippines, light clothing, made of natural fibres, a scarf for the breeze, a light sweatshirt for air-conditioned places, light raincoat or umbrella for the areas where it rains even in winter. In Baguio, at 1,500 metres (5,000 feet), spring/autumn clothes, light for the day, jacket and sweater for the evening. For the mountains, warmer clothes depending on altitude.

In summer: throughout the plains and the coasts, tropics-friendly clothing, a scarf for the breeze, a light sweatshirt for air-conditioned places, light raincoat or umbrella. In Baguio, at 1,500 metres (5,000 feet), spring/autumn clothes, jacket and sweater for the evening, raincoat. For the mountains, warmer clothes depending on altitude.
For the reef, equipment for snorkeling, water shoes or rubber soled shoes.