Sumatras

SUMATRA SQUALLS

SCOPE:-

• Overview

• Description

• Appearance

• Formation

• Locale

• Movement

• HAZARDS

SUMATRAS

OVERVIEW

“Sumatras” are lines of thunderstorms which usually occur between March and November each year. (SW monsoon)

These squalls (lines of thunderstorms) develop at night over Sumatra or the Malacca Straits and move east towards Singapore and Peninsular Malaysia usually during the pre-dawn and early morning.

They are often characterised by sudden onset of strong gusty surface winds and heavy rain lasting from 1 to 2 hours as they move southwards along the west coast of the Peninsular until it reaches Singapore in the early morning.

Maximum gusts of up to 26 metres per second (93 km/h) have been recorded during the passage of a Sumatra squall.

CONDITIONS REQUIRED -TS

LIFTING AGENT/TRIGGER

HOW ABOUT NIGHT?

HOW MANY HERE?

Between April – September

(Inter monsoon – mid March/mid October)

Nights in the Straits of Malacca.

Conditions are ripe for thunderstorms. How?

SOUTH WEST MONSOON

Although a thunderstorm can consist of just one ordinary cell that

transitions through its life cycle and dissipates without additional new

cell formation, thunderstorms often form in clusters with numerous cells

in various stages of development merging together. Unlike ordinary

single cells, cluster storms can last for several hours producing large

hail, damaging winds, flash flooding, and isolated tornadoes.

MULTI CELLS

SQUALL LINESSometimes thunderstorms will form in a line which can extend

laterally for hundreds of miles. These "squall lines" can persist for

many hours and produce damaging winds and hail. The rain

cooled air or "gust front" spreading out from underneath the squall

line acts as a mini cold front, continually lifting warm moist air to

fuel the storms.

LOCAL PHENOMENAS

...NITE IN THE STRAITS

• DIURNAL VARIATION OF SURFACE WIND

• KATABATIC WIND FROM SUMATRAN & MALAYSIAN HIGHLANDS

• ADIABATIC COOLING

• CONVECTION & CONVERGENCE

• HI – RELATIVE HUMIDITY

Rapid formation of Squall lines

…SO WHEN NITE FALLS

HAZARDS

• (Thunderstorms) HAIL

• DAMAGING WIND

• Wind shear at low levels.

• Heavy precipitation that can last for a few hours.

Degrades aircraft performance (& nav systems)

• Lightning