MANILA — Already inconvenienced by the frequent afternoon or evening heavy rains?

According to weather bureau PAGASA, the warm and dry season is not over yet.

"Based sa historical records, ang matataas na temperatures talaga na-re-record natin ng second part ng April at first half ng May," senior weather forecaster Glaiza Esculler told ABS-CBN News.

(Based on historical records, the highest temperatures are usually observed between the second half of April and the first half of May.)

The hottest temperature yet this year was recorded in Camiling, Tarlac on April 21 at 39.9 degrees Celsius.

The country's all-time heat record of 42.2 degrees Celsius was measured in Tuguegarao City on April 22, 1912 and May 11, 1969.

But as many have observed, since May started, the afternoon thunderstorms have been more frequent, not only in Metro Manila but also in other regions.

Flooding and heavy rush hour traffic were experienced in some parts of Metro Manila while areas in Sultan Kudarat, Cebu, and La Union also observed flash floods or landslides.

"'Pag [kinompare] ang April at May, although pareho namang mainit, pagdating ng May mas tumataas na 'yung humidity so mas nagiging conducive na ito for thunderstorm formation," Escullar explained.

(Both April and May are considered hot months. However, it is during May when humidity rises, which is more conducive to thunderstorm formation.)

TRANSITION PERIOD

Strictly speaking, the entire warm and dry season from March to May is considered the transition period between the cool and dry northeast monsoon or Amihan and the wet southwest monsoon or Habagat seasons.

But the more frequent afternoon rains are early signs that the country is nearing the start of the rainy season over the western part of the archipelago.

"'Pag buwan ng Mayo lalo pag nagiging regular na o nagiging madalas na 'yung thunderstorms sa hapon o gabi, ay isa 'yan sa mga early signs na mag-o-onset na tayo ng rainy season."

(More frequent afternoon or evening thunderstorms in May is among the early signs that the rainy season is nearing.)

The passage of two low pressure areas over central Philippines from the start of May also provided a lot of moisture that fueled the formation of thunderstorms.

Some areas may be more prone to thunderstorms than the others.

"'Pag malapit ka sa bundok o malapit ka naman sa body of water, sa ganitong mga buwan ng March, April, May, mas prone ka sa formation ng mga thunderstorm clouds," Escullar said.

(During the months of March, April, and May, mountainous areas or those around bodies of water, are more prone to thunderstorm clouds formation.) 

RAINY SEASON

PAGASA follows a set of criteria to determine whether the rainy season over the western section of the country has already started.

Five consecutive days of rain should be observed over more than half of the 13 monitoring stations in the western parts of Luzon and Visayas.

Winds blowing from the west or southwest should also be observed in these areas, from the ground up to a height of 1.5 kilometers.

Areas under Type I climate experience the Habagat rainy season. These include Metro Manila, Ilocos Region, western Cordillera, most of Central Luzon, Cavite, western Rizal and Batangas, Occidental Mindoro, western Palawan, and southwestern Panay Island.

They have two distinct seasons: dry from November to April and wet for the rest of the year. Maximum rain is experienced between June and September.

Last year, the rainy season started on May 29, when the passage of tropical cyclone Aghon triggered the Habagat.