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A heavy rain warning is displayed on this website when
a heavy rain warning is in force. The heavy rain warning serves to alert the
public on the actual or expected occurrence of heavy rain over any of the 5
sectors (north, south, east, west, central) across Singapore.
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Not all rain events
will be accompanied by warnings. As a guide, heavy rainfall refers to
rainfall with rates exceeding 50 mm in an hour and affecting more than
one-fifth of the island. The warning may be issued even if these rates are not
met when the rain is expected to be prolonged. The warnings could also be
issued after the rain has commenced if it is assessed that the rain is expected
to become heavy subsequently.
The lead time for
warnings usually ranges from 15 to 45 minutes depending on the nature of the
weather system causing heavy rain. For the small-scale convective thunderstorms
which frequently develop and dissipates quickly, the lead time
is generally shorter, about 15 minutes in advance of the heavy rain.
Longer lead times of 30 minutes or more are possible for larger scale systems
such as Sumatra squalls and Northeast Monsoon surges.
More Information on "Heavy Rain Warnings and Challenges in Weather Forecasting" is available under the FAQ section