MANILA — The shear line, an area where cold and warm air meet, dumped six weeks worth of rain in Northern Samar and spawned floods on Tuesday, the state weather bureau said.
Within just 24 hours, between Monday 8 a.m. and Tuesday 8 a.m., PAGASA's station in Catarman town recorded 619 millimeters of rain, more than its normal November rainfall of 457.8 millimeters.
This was higher than the 24-hour amount of rain during the passage of Tropical Storm Ondoy in 2009, at 454.9 millimeters recorded at the Science Garden in Quezon City.
The rainfall also topped the previous highest daily rainfall recorded in Catarman on December 2, 2019 at 605.5 millimeters.
Floods almost reached the second story of some houses in the towns of Catarman, Lope de Vega, and Catubig.
In Sorsogon, 185.0 millimeters of rain was recorded at the Juban station of PAGASA.
As of 11 a.m. Tuesday, red warning for heavy torrential rains was hoisted over Sorsogon, Northern Samar, Biliran, and the northern portions of Samar and Eastern Samar.
Orange warning level for intense rains was raised over the rest of Samar and Eastern Samar. Lastly, yellow warning level for heavy rains was in effect over Catanduanes, Camarines Sur, Albay, Masbate, northeastern Iloilo, northern Negros Occidental, and northern Leyte.
Shear line rains have been battering the Bicol Region and Eastern Visayas for around a week. A low pressure area that approached the region also added to the rains before it dissipated last Sunday.
PAGASA forecasts that the shear line will continue to bring heavy rains in Southern Luzon and Visayas until Wednesday.
The shear line forms only during the northeast monsoon or amihan season, when the cool northeast monsoon meets the warm and moist winds blowing from the Pacific. The difference in temperatures of the air masses allows big thunderstorm clouds to form and dump heavy rains.
Climate experts note that the warming atmosphere can hold more moisture that may lead to more severe rainfall events.