As the rain draws near: Thunderstorms in the Philippines

Have you felt the shift in the weather lately? To those in Manila, did you experience the sudden and heavy rainfall last Wednesday evening? It is not just the wind, but the sign of another season to come.

It is quite typical during the month of May when thunderstorms occur due to a steady increase in cloudiness, coupled with the frequent occurrence of heat transfer brought about by intense daytime heating, which gives thunderstorms power to build up fast. Thundery rains give a new lease of life to semi-parched lands amid their apparent semi-permanence.

May is also the time when “electrical” storms become more evident. These are thunderstorms. With rain beginning to fall later in the day or evening, they indicate the arrival of a transition period when condensation and evaporation rates accelerate further, despite the warm temperatures we have been experiencing for months. These rains somewhat decrease the hot and humid conditions people have been accustomed to. A thunderstorm is a kind of weather phenomena which brings dangerous lightning, thunder, and strong winds, resulting in brief but sometimes heavy downpours which can cause instant inundation to the unsuspecting and low-lying areas.

Regional climate driver

How do thunderstorms form? There is evidence of the migration of Intertropical Convergence Zone (ITCZ) along Indonesia and Papua New Guinea last mid-April, and the buildup of High Pressure Areas (HPAs) to the North of Australia recently. As such, winds tend to move poleward, bringing moister air and increasing the rate of precipitation over the West area.  The development of troughs or regions of low atmospheric pressure along Hainan Island, China stretching well into the Ilocos Norte and Cagayan provinces are good indicators too. This will intensify rain-producing clouds, which brings more frequency of rainfall across Luzon. Another is the prevalence of the weak Southwesterly surface wind flow coming from the West Philippine Sea. This will become the dominant wind system through the end of the month until it reaches its peak by late July or August.

The rainy season

The state weather bureau, the Philippine Atmospheric Geophysical and Astronomical Services Administration (PAGASA) will begin to monitor rainfall totals in select manned stations around the country in the days ahead. There is a particular criterion to satisfy before the agency officially declares the start of the rainy season, which is normally announced sometime in June. Two of these is the presence of the Southwest Monsoon (Habagat), and rainfall of 25 millimeters or more for five consecutive days in five major weather stations.

wpf_may_rainyseasonstart

Needless to say, the country is now in a transition period from the hot-dry season to a much anticipated rainy season, which is great news for everyone amid the dwindling water resources in many parts of the country. We can also expect the formation of tropical disturbances well to the East of Visayas or Mindanao in the coming weeks as evidenced by Tropical Disturbance (LPA) 90W which remains steady at about 1,100 km to the East of Tandag City, Surigao Del Sur. Should the system strengthen further, it will be named locally as ‘’Dodong’’ – the fourth Tropical Cyclone this year.

El Niño hangs on

With the current Weak El Niño still underway, there will be a significant reduction in average rainfall totals through August and September. And the issue of food security and water supply increases the complexity of its impact in several sectors of society.

The varying cycles and impacts of El Niño on rainfall distribution bring drought severity to a new level. These are hard to predict as they are complex. However, there are small incremental steps to avoid significant losses. An early warning system is one, and local climate adaptation measures can be put into place to address this problem by identifying vulnerabilities and potential risks. It is always good to be #WeatherWiser, especially in times of weather transitions.

Interested about being #WeatherWiser? Contact us at weatherwiser@weatherph.org.


–By Adonis S. Manzan
Typhoon Specialist, WeatherPhilippines Foundation, Inc.

Reference:

https://www.rappler.com/business/229052-el-nino-damage-agriculture-as-of-april-25-2019
http://bagong.pagasa.dost.gov.ph/
https://iridl.ldeo.columbia.edu/maproom/ENSO/ENSO_Info.html
http://glossary.ametsoc.org/wiki/El_ni%C3%B1o

 

 

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