NZ Weather Forum

Metservice wrote:Daytime heating and sea breeze wind convergences are expected to trigger afternoon and evening showers over inland parts of both Islands, especially from Gisborne to Wairarapa, including the Central Plateau and also from inland Nelson and Marlborough to North Otago.

For the ranges of Gisborne, Hawkes Bay, the eastern Bay of Plenty, eastern areas of Taupo and Taihape, and also the ranges of Nelson and Marlborough, there is a high risk of thunderstorms during the afternoon and evening with a moderate risk of isolated SEVERE THUNDERSTORMS developing, while for Wairarapa the risk of thunderstorms developing is considered moderate with a low risk that one or two may be SEVERE. SEVERE THUNDERSTORMS WATCHES have been issued.

These thunderstorms are expected to be slow producing localised heavy rain with intensities of 15 to 25mm/hr, as well as hail of 5 to 10mm in diameter. However with SEVERE THUNDERSTORMS localised downpours of 25-35mm/hr are possible.

Early in the evening, there is a low risk that thunderstorms drift from the ranges of the central North Island into the Bay of Plenty and most of Taupo.

Additionally, a lower risk of thunderstorms extends out from the main areas to take in the central North Island high country and inland areas of north Canterbury.

Finally, a front is forecast to move onto Northland late Monday, bringing increasing showers to the area. Some of these showers could be heavy, with a low risk of isolated thunderstorms from this afternoon.

Elsewhere, no thunderstorms expected.

Metservice wrote: Issued at: 10:34am Monday 18 Nov 2013

Daytime heating and sea breeze wind convergences are expected to trigger afternoon and evening showers over the central North Island during Tuesday. From central Hawkes Bay, across to Taranaki and then north to Waikato, Bay of Plenty and Gisborne, there is mostly a moderate risk of thunderstorms during the afternoon and evening, which could bring localised heavy rain of 10-25mm/hr and hail 5-10mm in diameter. However, in the ranges of Gisborne and the eastern Bay of Plenty, and also about western parts of Waikato and Waitomo, the risk of thunderstorms is considered high, with the potential that localised heavy rain rates could exceed 25mm/hr in these areas.

Additionally, in the west of Northland there is low risk of thunderstorms during the afternoon and evening.

Elsewhere, no thunderstorms expected.

NZstorm wrote:A problem with this set up is there is no low level cap, so showers develop freely and weaken afternoon instability.

Tornado Tim wrote: Id expect a line to develop from North Waikato down to central mid Waikato, where the winds meet. The stuff preceding that will be unorganised and should collapse quickly. ie: dont chase that stuff.......

jamie wrote:High risk of severe today. Wahoo

Metservice wrote: Daytime heating and sea breeze wind convergences are forecast to trigger showers over inland parts of both Islands from late morning. The most unstable conditions are expected about central parts of the North Island under a cold upper level trough, where there is a high risk of scattered thunderstorms this afternoon and early evening. For inland areas from Waikato to Taranaki and across to the main ranges of Gisborne and Hawkes Bay, these storms will be slow moving and as a result have the potential to be SEVERE producing localised downpours of 25 to 40mm/hr, along with hail. Rainfall of this intensity can cause surface and/or flash flooding as well as slips, and may make driving hazardous. Heavy showers and thunderstorms should diminish into the evening hours. Outside the central high risk area, there is a lower risk of isolated thunderstorms from western parts of Northland to northern Manawatu and Central Hawkes Bay as indicated on the chart.

Over the South Island, isolated afternoon and early evening showers are most likely over the ranges from Nelson and Buller down to the Mackenzie, as well as inland parts of Southland, Clutha and Central Otago. There is a low risk of one or two showers turning thundery in these areas.

Elsewhere, no thunderstorms expected.