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Saturday, December 9, 2023

Vigilance vs. flash floods

Meteorologists have raised a warning for people to be vigilant while experiencing rains due to the shear line and the northeast monsoon.

Aircraft and ships are also forewarned with this wind shear phenomenon, the change in speed and direction of wind over a short distance, most often caused by microbursts (really small yet intense downbursts from thunderstorms), temperature inversions (when the temperature of the air gets colder as you get closer to the surface of the Earth), and surface obstructions.

The northeast monsoon is rainy weather caused by northeasterly winds affecting much of the tropics from December to March.

With this shear line, moderate to strong winds and moderate to rough seas will prevail over Luzon, the Visayas, and the northern section of Mindanao, and rough to very rough seas are forecast over the seaboards of Northern Luzon, the eastern seaboard of Central Luzon, the eastern and western seaboards of Southern Luzon, and the eastern seaboard of the Visayas.

Sea travel is risky for small seacraft, and mariners of these vessels are advised to seek safe harbor.

It’s heartening that at least six domestic flights were canceled Tuesday for the safety of passengers.

We heard the weathermen warning people in the affected areas to stay vigilant against possible flash floods or landslides during moderate to heavy rains caused by the ITCZ and shear line.

The ITCZ, known by sailors as the doldrums or the calm because of its monotonous windless weather, is the area where the northeast and the southeast trade winds converge and encircles the Earth near the thermal equator though its specific position varies seasonally.

The shear line, an area where warm and cold air meets, is a narrow corridor along which there is an abrupt change in the horizontal component of the wind, observed both near the ground and in jet streams, where it may be associated with clear-air turbulence.

Vertical wind shear that causes turbulence is closely associated with the vertical and horizontal transport of momentum, heat, and water vapor.

Hypervigilance is needed since the shear line, according to weather forecasters, has dumped six weeks worth of rain in Northern Samar and spawned floods on Tuesday.

Catarman town alone recorded 619 millimeters of rain, more than its normal November rainfall of 457.8 millimeters, and higher than the 24-hour amount of rain during 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 Dec. 2, 2019 at 605.5 millimeters.

An alarming scene showed floods almost reaching the second story of some houses in the towns of Catarman, Lope de Vega, and Catubig in Samar.

Precaution is a pressing priority.

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