Storms Central & Eastern 13/12/2017
Posted: Wed 13/12/2017 09:10
Possible storms today is worthy of a thread considering the severe threat for northern half of Canterbury and Marlborough, as well as Gisborne and northern Hawkes Bay
From the Met Service
Valid to: Midnight Wednesday 13 Dec 2017
Issued at: 8:39am Wednesday 13 Dec 2017
Temperatures aloft are expected to cool this afternoon and evening bringing instability to many central and southern areas.
This cooling combined with low level wind convergences should lead to daytime cloud buildups producing scattered showers and thunderstorms about Gisborne and Hawkes Bay during the afternoon and evening. These thunderstorms will be accompanied by localised heavy rain and hail. There is a low risk a few of the thunderstorms could be severe over Gisborne and northern Hawkes Bay producing localised downpours in excess of 25mm/hr and large hail. Rainfall rates of this intensity can cause surface and/or flash flooding, while large hail can cause damage to crops.
Further south, a freshening south to southeast flow and cooling aloft is expected to lead to thunderstorms embedded within broader areas of rain about parts of Buller, Marlborough and inland Canterbury during the afternoon and evening, with localised heavy rain of 10-25mm/hr and hail. Additionally there is a low risk a few of the thunderstorms could be severe in the hills and ranges of Canterbury and Marlborough producing localised downpours with rates of 25 to 35mm/hr.
As this southeasterly wind change pushes through Nelson and the lower North Island late in the day, there is a moderate risk of the change triggering thunderstorms about parts of Whanganui, Manawatu, Horowhenua, Wairarapa and Nelson from this evening with localised heavy rain and hail.
A broad low risk of thunderstorms covers remaining parts of central and southern New Zealand through much of the period, as indicated on the chart.
From the Met Service
Valid to: Midnight Wednesday 13 Dec 2017
Issued at: 8:39am Wednesday 13 Dec 2017
Temperatures aloft are expected to cool this afternoon and evening bringing instability to many central and southern areas.
This cooling combined with low level wind convergences should lead to daytime cloud buildups producing scattered showers and thunderstorms about Gisborne and Hawkes Bay during the afternoon and evening. These thunderstorms will be accompanied by localised heavy rain and hail. There is a low risk a few of the thunderstorms could be severe over Gisborne and northern Hawkes Bay producing localised downpours in excess of 25mm/hr and large hail. Rainfall rates of this intensity can cause surface and/or flash flooding, while large hail can cause damage to crops.
Further south, a freshening south to southeast flow and cooling aloft is expected to lead to thunderstorms embedded within broader areas of rain about parts of Buller, Marlborough and inland Canterbury during the afternoon and evening, with localised heavy rain of 10-25mm/hr and hail. Additionally there is a low risk a few of the thunderstorms could be severe in the hills and ranges of Canterbury and Marlborough producing localised downpours with rates of 25 to 35mm/hr.
As this southeasterly wind change pushes through Nelson and the lower North Island late in the day, there is a moderate risk of the change triggering thunderstorms about parts of Whanganui, Manawatu, Horowhenua, Wairarapa and Nelson from this evening with localised heavy rain and hail.
A broad low risk of thunderstorms covers remaining parts of central and southern New Zealand through much of the period, as indicated on the chart.
