Lec 8A - Weather Systems in the Philippines

High-Pressure Area (HPA)

Area where winds sink and diverge at surface; associated with clear weather and light winds

Ridge of High-Pressure Area

Elongated area of relatively high pressure extending from a high-pressure center

Low-Pressure Area (LPA)

Area where winds converge at surface and rise; often moist/warm, can form storms in the Philippines

Easterlies

Trade winds blowing from east to west; bring weather from the Eastern Pacific to the Philippines

Intertropical Convergence Zone (ITCZ)

Band of clouds/thunderstorms where NE and SE trade winds converge; active over NCR in May-Jun and Sep-Oct

Southwest Monsoon (Habagat)

June-Sep; warm/moist winds from SW; brings moderate-heavy rains to western Philippines

Northeast Monsoon (Amihan)

Nov-Mar; cold/dry winds from NE; brings slight-moderate rains to eastern Philippines

Front

Transition zone between two air masses with contrasting temperature and humidity

Stationary Front

Front with essentially no movement; winds blow parallel but opposite on either side

Cold Front

Zone where cold air replaces warm air; steep leading edge; brings narrow band of thunderstorms

Criteria for Cold Front

Sharp temp change, moisture change, wind shift, pressure change, specific cloud/precip patterns

Frontolysis

Weakening of temperature contrast across a front, causing it to dissipate

Frontogenesis

Strengthening of a front due to increasing temperature contrast

Tail-end of Cold Front (Shear Line)

Formed by cold Amihan and warm Easterlies; produces cool NE winds with precip in eastern PH (Nov-Apr)

Warm Front

Formed as warm air advances over cold air mass; gentler slope than cold front

Occluded Front

Formed when a cold front overtakes a warm front; violent weather at occlusion point

Thunderstorm

Convective storm with rising air; forms in conditionally unstable environment

Ordinary Cell Thunderstorm

Scattered storm with limited wind shear; goes through cumulus, mature, dissipating stages

Cumulus/Growth Stage

Initial stage with updrafts; cloud grows vertically; no lightning/precip yet

Mature Stage

Appearance of downdrafts; most intense with heavy rain, lightning, thunder, gusty winds; gust front forms

Gust Front

Boundary between cold downdraft and warmer air; enhances updrafts

Dissipating Stage

Updrafts weaken, downdrafts dominate; light precipitation; cloud evaporates

Multicell Thunderstorm

Contains several cells in different stages; forms in moderate-strong wind shear; longer-lived

Supercell Thunderstorm

Large, long-lasting storm with single rotating updraft; forms in very strong wind shear; can produce tornadoes

Wall Cloud

Rotating cloud descending from a supercell; indicates strong updraft and potential tornado formation

Heavy Rainfall & Floods

Occur when thunderstorms stall; cause rapid rising flood waters

Hail

Formed by intense updrafts keeping hailstones in cloud for extended growth

Lightning

Electrical discharge within cloud, cloud-to-cloud, cloud-to-air, or cloud-to-ground

Thunder

Sound from explosive air expansion due to lightning heat

Lightning Safety

Go inside, avoid appliances/water, don't shelter under trees, if hair stands end lie flat is wrong

Tornado

Rapidly rotating column of air around intense low pressure; funnel cloud if circulation doesn't touch ground

Fujita Scale

Scale from F0 (weak) to F5 (incredible) rating tornado damage based on wind speed