Eastern Indian Ocean climate

North-east Monsoon - November to March

  • Winds generally north-easterly.
  • Frequent showers and thunderstorms over and to the east of high ground; more scattered to the west.
  • Main threat: eastern India, Sri Lanka, north Sumatra, Andaman and Nicobar Islands.

Transitional season - April to May

  • Wettest near the convergence zone as it moves north.
  • Generally cloudy with showers and thunderstorms frequent at times.
  • Wind begins to turn south-westerly.
  • Very isolated tropical storms mainly in the east.

South-west Monsoon - June to September

  • Winds generally south-westerly.
  • Frequent showers and thunderstorms over and to the west of high ground; more scattered to the east.
  • Main threat: western India and Sri Lanka, north and west Sumatra, Andaman and Nicobar Islands, western Thailand.

Transitional season - October to November

  • Wettest near the convergence zone as it moves south.
  • Generally cloudy with showers and thunderstorms frequent at times.
  • Wind begins to turn north-easterly.
  • Very isolated tropical storms mainly in the east.

All seasons

  • Maximum temperatures 28-33 °C, minimum temperatures 23-27 °C, high humidity.
  • Winds generally light but increasing significantly in or near heavy showers and thunderstorms.
  • Squalls possible mainly in Sumatra and Thailand.
  • Rainfall totals in excess of 50 mm/hour and 300 mm/day possible.

Effects on operations

  • Hazards due to the heavy showers and thunderstorms, i.e. reduced visibility, lower cloud bases, strong winds and gusts, severe icing and turbulence. Poorer conditions generally short-lived.
  • Heavy showers potentially leading to flooding, possibly without warning, and damage to the local infrastructure.
  • Generally high temperatures and humidity leading to high heat-stress values.
  • Isolated squalls and very isolated tropical storms.

Last updated: 17 December 2013