Thu, 28 Oct 2004
Metservice On The Lookout For Severe Thunderstorms
From 1 November 2004, MetService will be providing a new severe
Convection advisory service, funded by the Minister of Transport. Severe convection concerns the development of intense
localised storms associated with thunder, lightning, heavy or torrential downpours of rain, large hailstones, hail
accumulation and sudden bursts of gale force winds.
MetService's Chief Forecaster Rod Stainer said, "Severe convection events are very localised and are not covered in the
existing severe weather warning system which relates to widespread events." Mr Stainer went on to say that severe
convection is not uncommon in New Zealand and the impacts are wide ranging, for example -
Sudden localised flooding occurred in Wellington on 10 January 2001 after 52mm of rain fell in 45 minutes, resulting in
parts of the CBD becoming knee deep in water. - The stability of a dam behind Picton was threatened on 16 February 2003
after 85mm of rain fell in one hour. - Hailstones of golf ball size fell in Masterton on 7 January 2001 and considerable
damage was done to some orchards, windows were broken and cars damaged with overall losses estimated at $5 million. –
Large accumulations of hail occurred in Wellington on 12 September 2002 resulting in disruptions to traffic and aircraft
operations, and in Wanganui on 6 April 2004 causing damage to the roofs of homes and buildings. - Sudden windstorms
associated with a squall line crossed the Auckland area on 31 October 2001 with gusts of 150 km/h and caused significant
damage to properties from Helensville to Mangere.
The new Severe Convection Outlook service will provide emergency managers around the country with valuable information
to assist them in their "readiness" role. Marshall Hyland, Porirua City Council's Emergency Manager who worked closely
with MetService forecasters last summer testing this new service said, "The outlooks for severe convection provided us
with vital advance notice of sudden heavy downpours and allowed us to identify potential problem areas."
Mr Hyland went on to say that severe convection advice received on 19 February 2004 allowed for early activation of the
Emergency Incident Room and pre-event briefing of fire crews and police. Severe thunderstorms overnight on the 19
February resulted in localised flash flooding around the Wellington region.
Mr Stainer cautioned that these Outlooks are not the complete answer. He said, "While they will describe the broad
areas that are at risk to severe convective activity they will not supply precise information on exactly when and where
these localised storm will hit."
Mr Stainer went on to say that over the next 12 months or so MetService will work towards the development of severe
convection "watches" which will contain more detailed information concerning the areas that are likely to be most
affected in the immediate 4-6 hour period.
Eventually MetService hopes it can supply, with the aid of its Doppler weather radars, detailed warnings for precise
locations. However, this will require considerable research and development, and it may be as much as 4 or 5 years
before such a service is available.
The Severe Convection Outlooks will be freely available to the public on the MetService web site at