Climate Information
Rainfall
Rainfall in Ilocos Norte is principally brought about by the Southwest Monsoon and Tropical cyclones. Thunderstorms also contribute to the rainfall received in the province.
Based from 45 years (1976-2020) of rainfall data, the annual rainfall is 2082.9 mm. About 80% of this occurs from June to September. The highest rainfall amount usually occurs in August, while negligible rainfall occurs during January, February, March, April, November, and December
Evaporation
Annual evaporation in Batac, Ilocos Norte is about 1784.4 mm. Highest evaporation generally occurs during the month of April with a total of 189.9 mm (6.3 mm/day). Highest solar radiation (23.5 MJ/m2/day) and lowest relative humidity (75%) are observed during this period
Superimposing evaporation data to that of the rainfall data, it can be observed that rainfall is in excess during the rainy season but deficit during the dry season
Air Temperature
The annual mean daily temperature is 27.3oC (maximum, 32.4°C and minimum, 22.1°C). The coolest month of the year is January, while April and May, the hottest
Solar Radiation and Relative Humidity
On the average, daily solar radiation is 19.3 MJ/m2/day. Solar radiation values are low during the rainy season and short day periods of the year (October to February). Values of relative humidity is inversely proportional to solar radiation i.e. when the solar radiation is high, the relative humidity is low and vice versa. Relative humidity is above 80% except in April and May. The average relative humidity is 82%
Wind Speed
The daily mean wind speed at 1-km height is about 41 km/day. The highest recorded mean monthly is June (40.6 km/day) and the lowest (26.5 km/day) is October.
Wind Direction
The prevailing wind system in Ilocos Norte are as follows: a) the Southwest Monsoon affects the province in June to August. b) the Northeast Monsoon affects the province in October to November. The wind coming from the North starts from the month of December and ends in February. c) the trade wind (varying directions) dominates the province from March to April
Wind direction
| Jan | Feb | Mar | Apr | May | June | Jul | Aug | Sept | Oct | Nov | Dec |
|---|---|---|---|---|---|---|---|---|---|---|---|
| N | N | N-NW | W-WN | W | SW | SW | SW | E | NE | NE | N |
Length of day (sunrise to sunset)
Longest days occur in June (13.10 hrs) and short days begin in October to February. Shortest days occur in December (11.05 hrs).
Tropical cyclones
Nine of the 20 tropical cyclones entering the Philippine Area of Responsibility (PAR) affect directly the province of Ilocos Norte. Most of these occur during the wet season. On the average, about 3 cyclones each occurred in the months of July and August, and one each in the months of June, September, and October. Higher probabilities of tropical cyclones occur from June to October with the highest probability occurring during the month of August. This coincides with the highest rainfall also occurring during that time.
