If you are planning to fly to the Philippines around Christmas/New Year holidays or Easter, make sure to book your flight tickets several months in advance. One in ten Filipinos works abroad and they often return home for holidays, thus air tickets for holiday periods are expensive and hard to get.
Monsoon season in the Philippines lasts from June till September. It is followed by the dry seasons during which travel in the Philippines is most pleasant. It gets hot in April and in May; the heat accompanied by high humidity becomes almost unbearable. It is best to visit the Philippines between November and May (heavy rain might still occasionally hit the country in September and October). Between November and May the weather is generally nice and there are no typhoons. However, it might get cold in the Cordillera in winter months.
Travel to the Philippines during the monsoon season is not impossible, but it is often difficult. Some roads become impassable, ships can be delayed for several days and there are frequent flight cancellations. On the other hand, there are much less tourists travelling in the Philippines during the monsoon season thus prices of accommodation drop considerably.