Weather Patterns: Low-Pressure Areas

Low-Pressure Areas (LPA)

• LPA is a region with lower atmospheric pressure compared to surrounding areas.
• LPAs are often precursors to tropical cyclones and typhoons.
• Meteorologists use pressure drops to forecast weather changes.

Formation of LPAs

• Warm evaporation from ocean waters rises, creating low pressure below.
• Vapor thickens into clouds which are moved by storm winds.
• Clouds condense and precipitate as rain.
• Gases move from high-pressure areas (HPA) to LPA, forming winds.

Hydrometeorological Hazards

• These are natural atmospheric or oceanic processes that can lead to loss of life or damage.
• Hazards include tropical cyclones, floods, and storm surges.

Tropical Cyclones

• Large storms characterized by a low-pressure area and powerful winds.
• They gain strength over bodies of water and weaken when moving inland.
• Areas hit by cyclones experience strong winds, heavy rainfall, and high sea waves.

Destructive Effects of Cyclones

• Strong winds can damage structures, vehicles, and topple trees.
• High-speed winds can capsize vessels and project dangerous debris.
• PAGASA categorizes cyclones based on wind speed for public safety.

Preparedness for Cyclones

• Regular occurrences have made Filipinos adept at cyclone preparation.
• Pre-cyclone measures include securing tree branches, reinforcing roofs, and boarding windows.
• Local Government Units (LGUs) must identify at-risk communities prior to storms.

Flooding as a Secondary Hazard

• Heavy rainfall from cyclones leads to flooding, which can be gradual or sudden (flash floods).
• Flooding areas are categorized based on potential floodwater heights: low (up to 0.5 m), moderate (up to 1.0 m), and high (above 1.0 m).
• Low-lying areas serve as basins for floodwater, increasing vulnerability.

Impact of Flooding

• Flooding can result in structural damage and physical hazards, leading to biological risks.
• Historical floods have caused outbreaks of diseases like leptospirosis.
• Local governments are encouraged to invest in flood prevention measures, including floodgates and adequate drainage systems.

Storm Surges

• A storm surge arises from rising sea levels and powerful waves during a tropical cyclone.
• Strong winds push coastal waters, amplifying wave heights, posing risks to coastal communities.
• The catastrophic effect of Super Typhoon Yolanda in 2013 exemplified the deadly nature of storm surges, causing extensive destruction in Tacloban with waves up to 7 meters high.