Tropical Cyclones: Eye, Eyewall, and Rainbands

Tropical Cyclones

• Intense, low-pressure storm systems characterized by strong winds and heavy rains.
• They are composed of bands of clouds in a tight, rotating spiral.

Eye

• The calm center of a hurricane.
• It appears as a hole in the storm, typically with clear and calm weather.
• The spiral's center extends 30 to 60 kilometers in diameter and has little to no rainfall with calm winds.

Eyewall

• It is a ring of towering thunderstorms, the location of the most severe weather within a cyclone.
• Encircles the eye and has the heaviest precipitation and strongest winds.
• It is the most dangerous part of a hurricane.

Rainbands

• Spiraling clouds that surround the eye and can produce heavy rains.
• Are capable of producing heavy rain and strong winds, though less intense than those in the eyewall.

Misconception Alert

• A period of calm during a typhoon is caused by the eye passing over an area.
• Violent winds and torrential rain can be expected from the eyewall after the eye passes.
• The eyewall has the strongest wind speed and the heaviest rain.

Tropical Cyclone Formation Areas

• Tropical cyclones form in seven oceanic basins:
• North Atlantic Ocean
• North Indian Ocean
• Eastern Pacific Ocean
• Southwest Indian Ocean
• Western Pacific Ocean
• Australian region
• Southern Pacific Ocean
• Each basin is monitored by a Regional Specialized Meteorological Center (RSMC).
• The Western Pacific region, where Asia is located, is monitored by the Japan Meteorological Agency (JMA).

Types of Tropical Cyclones

• Hurricanes: Form in the North Atlantic and Eastern North Pacific Ocean.
• Cyclones: Form in the Bay of Bengal, Arabian Sea, and Western Southern Indian Ocean.
• Typhoons: Form in the Western North Pacific Ocean.

Tropical Storm Formation

• Stage 1: Tropical Storms Formation - A low pressure area occurs when warm sea air rises, bringing surrounding air inflowing, causing increased winds.
• Stage 2: Tropical Storms Formation - Warm air continues to rise creating moisture, which cools and condenses into storm clouds
• Stage 3: Tropical Storms Formation - Once the cool air descends, a calm area forms called the "eye". Winds near the equator move the storm from East to West, the Earths spin causes the wind to spin, starting to swirl into a cyclone.

Landform and Water Body Effects

• Tropical cyclones weaken after landfall due to being cut off from warm, moist air sources, which reduces condensation and heat release.
• Mountains interrupt cyclones and surface winds:
  • Moist air moving inland from the ocean is forced up a mountain range.
  • The rising air cools and expands, losing moisture as rain or snow on the windward side.
• Windward Side:
  • The side of the mountain facing the wind.
  • As wind blows, it pushes the moist air up the slope.
  • Often lush and green with more vegetation due to frequent rainfall.
• Leeward Side:
  • The mountain side faces away from the wind.
  • By the time the air reaches this side, it has already lost much of its moisture.
  • Descending dry air warms up, creating drier conditions and a rain shadow with a desert-like environment.
• Air descends, warms and releases a small amount of moisture and it weakens over the leeward side.
• Flat landforms, such as plains, do not effectively stop wind flow.
• Tropical cyclones disperse and weaken when moving:
  • Over land.
  • Towards the poles.
  • The above are compounded when encountering colder and drier air.

Typhoons in the Philippines

• Typhoons can occur anytime, most common from June to September.
• Approximately 20 typhoons enter the country annually, with about five being potentially devastating.
• Typhoon Yolanda in 2013 was the deadliest based on record.
• Tracked by PAGASA.

Philippine Area of Responsibility (PAR)

• PAGASA monitors PAR.
• PAR refers to the Philipines’ designated area in the Northwestern Pacific bounded by the lines joining specific points in the area.
• Typhoons generally originate in the region around the Mariana Islands (Western North Pacific Ocean).
• Most typhoons hit Luzon because it is along the country's latitude with the Islands.

PAGASA Classification

• PAGASA classifies typhoons by intensity, measured by maximum sustained wind speed near the eye.
  • Tropical Depression (TD): Less than 62 km/h
  • Tropical Storm (TS): 62 to 88 km/h severe
  • Severe Tropical Storm (STS): 89 to 117 km/h
  • Typhoon (TY): 118 to 184 km/h
  • Super Typhoon (STY): 185 km/h or above

Typhoon Preparedness in the Philippines

• PAGASA issues typhoon and storm warnings before an occurance.
• In 2022, a five-scale modified Tropical Cyclone Wind Signal (TCWS) was introduced.
• The TCWS is based on wind intensity and potential impact on human life and property.
• The National Disaster Risk Reduction and Management Council (NDRRMC) plans for and mitigates the effects of typhoons and other natural disasters.
• The NDRRMC is composed of different governmental, non-governmental, civil and private organizations.

Primary Effects

• Strong winds, heavy rain, and storm surges cause:
  • Buildings to be destroyed or flooded
  • Damage to infrastructure such as roads and railways
  • Loss of lives of civilizations and animals

Secondary Effects

• Secondary effects result from the primary effects:
  • Shortage of food and clean water
  • Job losses
  • Economic costs
  • Landslides