LA NIÑA ADVISORY   No. 8

The La Niña event has shown signs of further weakening in the tropical Pacific. Computer models continue to predict the return to neutral conditions across the Pacific likely by June.

Rainfall conditions in the country during April was affected by the following weather systems: the tail-end of the cold front, the easterly wave, the ridge of high pressure area, the inter-tropical zone (ITCZ), and one (1) tropical cyclone. Tropical Storm “Ambo”, (April 14-15), embedded along the ITCZ, was the first tropical cyclone to enter and cross the country this year through the southern portion of Visayas towards Palawan area. It brought moderate rainfall over the affected areas. For the month, above normal rainfall condition was observed over the Visayas, most parts of Mindanao, most areas of Southern Luzon including the Bicol region, and some areas in the western and Central Luzon. The rest of the country experienced near to below normal rainfall condition. For the last four months, above normal rainfall values were noted in the Visayas area, Bicol region, and Northern Mindanao, a manifestation of the recent La Niña impact. Likewise, above normal rainfall was also observed in some portions of Western Luzon although not significant enough to cause flooding.

Surface air temperature during the month was slightly cooler compared to last year in terms of maximum, while slightly warmer night time temperatures were observed. This was due to the cloudy conditions during the day. The actual ranges recorded were as follows: 22 – 36°C in Luzon while 16 – 25°C over its mountainous areas; 23 - 34°C in Visayas; 22 – 33°C in Mindanao and 18 – 30°C over its mountainous areas. (View Rainfall Charts)

Warm and humid weather condition in April due to normal surface heating during the month initiated the thunderstorm activity. Manifestations of the development of weather pattern in the Asian continent (appearance of heat lows) signals the coming of the rainy season in the country. The onset of the rainy season associated with the southwest monsoon is expected to be on the second half of May onwards. The occurrence of a tropical cyclone during the month may trigger the usual onset of the rains.

Weather systems likely for the month of May are the southwest monsoon, ITCZ, monsoon trough, and one (1) or two (2) tropical cyclones. Above normal rainfall conditions are expected over Visayas, Bicol region and most areas of Central and Southern Luzon, including many portions of Ilocos region, Cordillera Administrative Region (CAR) and Mindanao. The rest of the country will likely experience near to below normal rainfall. Forecasted ranges of temperature will be 23 - 36°C in Luzon and 16 – 25°C over its mountainous areas; 24 – 34°C in Visayas; 23 – 34°C in Mindanao and 19 – 30°C over its mountainous areas. Surface air temperature over the country is expected to be near normal.

PAGASA will continue to monitor the day-to-day rainfall/weather conditions and the large-scale climatic patterns that will affect the country. Updates/advisories on the on-going La Niña shall be issued as appropriate.