Because of its latitude, the country's climate is tropical: warm, humid, and fairly consistent from year to year. Because of its topography, Cagayan has three types of climate. Type I climate prevails in Sta. Praxedes and in western Claveria, which have two pronounced seasons: wet, May to October and dry, the rest of the year. Type III climate is experienced in the eastern part of the Sierra Madre mountains and in the Babuyan group of islands, where rainfall is evenly distributed throughout the year mainly because of the northeast tradewinds. This further enhances the economic potential of the level land along the Pacific coast of the province.

The rest of the province, which consists of the valley floor, has Type II climate, and that means no pronounced season: relatively wet from May to October. Maximum rain periods are not very pronounced and dry seasons last from one to three months.

From November to January, the northwest monsoon from East Asia brings dry and cool winds to this valley floor. Because of the open coastline in the north, this part of the province feels the full impact of this phenomenon, which could mean cold mornings and evenings, with average temperatures ranging from 18° to 21° Celsius. The tradewinds from the Pacific are blocked by the Sierra Madre range. Being on the leeward, this part has hot and dry climate in summers from February to May, with average temperatures ranging from 30° to 38° Celsius. From June to October, the southwest monsoon from the Southern Hemisphere brings heavy rainfall as it blows over the mountains. This heavy rainfall extends to the early part of November. During these months, rainy days could average 11 to 20 days a month. Being sheltered by the Sierra Madre Mountains the prevailing winds are north and northwest in the valley floor of Cagayan. This part of the province is driest in February to March.

The Isohyetal Map of Northern Luzon shows the average amount of rain in the different parts of the province. The valley floor of Cagayan receives 1,500 to 2,000 mm. of rain per year. Except for the Sierra Madre Mountains which have 3,500 to 4,000 mm. of rainfall per year, the rest of the province receives 2,000 to 3,500 mm. of rainfall per annum.