About cyclones

The official Northern Territory cyclone season runs from 1 November to 30 April.

Cyclone severity categories

The severity of a tropical cyclone is described in terms of categories ranging from 1 to 5 related to the zone of maximum winds. An estimate of cyclone severity is included in all tropical cyclone advices.

The Bureau of Meteorology (BOM) Warning Service is not designed to give an exact statement of conditions at individual locations but will give a general idea of the expected worst conditions. Using this severity scale, communities will be able to assess the degree of cyclone threat and take appropriate action.

Category

Strongest gusts (km/h)

Indicative typical effects

1-Tropical Cyclone

Gales - less than 125kmh Gales

Minimal house damage. Damage to some crops, tree and caravans. Boats may drag moorings.

2-Tropical Cyclone

Destructive winds - 125-164kmh 

Minor house damage. Significant damage to signs, trees and caravans. Heavy damage to some crops. Risk of power failure. Small boats may break moorings.

3-Severe Tropical Cyclone

Very destructive winds - 165 -224kmh  

Some roof and structural damage. Some caravans destroyed. Power failure likely. Boats will break moorings

4-Severe Tropical Cyclone

Very destructive winds - 225-279kmh 

Significant roofing and structural damage. Many caravans destroyed and blown away. Dangerous airborne debris. Widespread power failures.

5-Severe Tropical Cyclone

Extremely destructive winds - more than 280kmh

Extremely dangerous with widespread destruction

Cyclone warning stages

The Department of Infrastructure, Planning and Logistics (DIPL) will operate under the umbrella of the Darwin Port Cyclone Management Stages for the facilities at Frances Bay Mooring Basin. Darwin Port uses a six stage plan to manage its response to a cyclone, which is aligned to the Northern Territory Government (NTG) Emergency Response Group for counter disaster region 1.

Response stages

Description

Pre-season readiness

Cyclone response plans reviewed and updated.

Stage 1 - Cyclone watch (48hrs)

Declared when a tropical low or tropical cyclone exists and gale force winds are likely to affect Greater Darwin within the next 48 hours but not before 24 hours.

Stage 2- Cyclone watch (24hrs)

Declared when a tropical low or tropical cyclone is expected to cause gale force winds in Greater Darwin within 24 hours.

Stage 3- Cyclone warning (12hrs)

Declared when available information suggests that destructive winds are likely affect Greater Darwin within the next 6 – 12 hours.

Stage 4- Safety management and lockdown

At this time an official announcement is made by Northern Territory Emergency Services advising all persons in Greater Darwin to take shelter.

Stage 5- Destructive winds reach Greater Darwin

Declared when destructive winds have reached the boundary of Greater Darwin.

All-clear pending

Declared when winds no longer pose a threat to communities within Greater Darwin.  Note that the all clear is not declared at this time and a Stage 5 may be re-declared if necessary.

Stage 6 – All-clear

Declared when it is considered safe for the public to leave shelter.

The following two stages are not official stages, but are used in the operational response.

Post cyclone recovery

The recovery phase is managed by the Chief Minister’s office and is aimed at returning Greater Darwin back to normal.

Stand down

Declared when the Greater Darwin Controller considers that no further counter disaster measures are necessary.

Other information services

The Bureau of Meteorology also provides the following cyclone information services throughout the cyclone season.

Tropical cyclone seasonal outlook

This is issued at the beginning of the season to provide an estimate of the level of tropical cyclone activity in the coming season.

Tropical cyclone outlook

These are issued daily throughout the tropical cyclone season. They provide a forecast up to three days in advance of the probability of cyclone development in the seas around Australia.

Tropical cyclone information bulletin

These are issued when a cyclone is active in the Australian region, but is not expected to impact land-based communities within 48 hours

Tropical cyclone   watch

A watch is issued if a cyclone is expected to affect coastal communities within 48 hours, but not expected within 24 hours.

Tropical cyclone   warning

A warning is issued if a cyclone is affecting or is expected to affect coastal communities within 24 hours.

Marine warnings

Marine Warnings are issued for high seas and coastal waters threatened by cyclones. Additional information can be obtained from the BOM website: http://www.bom.gov.au/cyclone/about/warnings/

A DP cyclone response is triggered by the declaration of a cyclone watch or warning but response actions may be initiated prior to either a watch or warning being declared if the CMT considers early action warranted.

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Last updated: 13 October 2017