East Coast deep low 25/26 June 2024

[harleyb]

Looks as though the low developing off the North Island might tuck in closer to the Gisborne region than was expected a couple of days ago. An interesting couple of days coming up for that neck of the woods.

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[Blowy]

100mm plus for HB also likely by the look

[NZ Thunderstorm Soc]

100mm plus for HB also likely by the look

Another Gabrelle?, I hope not

[Ash]

Weather bomb. It's going to get stormy. Drive with care.

[Razor]

Fishing boat missing off Gisborne. Not good with this system.starting to wind up. Hope there is a successful search outcome

[NZ Thunderstorm Soc]

Weather bomb.

Maybe not. A weather bomb has to drop 24 hPa in 24 hours. This may night reach this, but then you may never know.
....anyway we had 10mm more rain overnight but it had eased off by dawn. A grey overcast morning but in the afternoon it started to clear with it becoming sunny later this afternoon, however it did cloud up this evening with some drizzle around 10pm. 10.5C for today. Calm day with no wind.

[Kobi]

Weather bomb.

Maybe not. A weather bomb has to drop 24 hPa in 24 hours. This may night reach this, but then you may never know.

The GFS model has a 1006mb - 983mb change in 24 hours, so its just 1mb short of being classifiable as a weather bomb, the ECMWF has a change of 1007mb down to 985mb in 24 hours, which is just 2mb short of being classifiable, so it will be close if it actually becomes one or not, though knowing how the term is misused in our country, it wouldn’t surprise me if its called one anyways.

[TonyT]

Maybe not. A weather bomb has to drop 24 hPa in 24 hours. This may night reach this, but then you may never know.

The GFS model has a 1006mb - 983mb change in 24 hours, so its just 1mb short of being classifiable as a weather bomb, the ECMWF has a change of 1007mb down to 985mb in 24 hours, which is just 2mb short of being classifiable, so it will be close if it actually becomes one or not, though knowing how the term is misused in our country, it wouldn’t surprise me if its called one anyways.

Bombogenesis, or more correctly explosive cyclogenesis, is latitude dependant. At 60degS a deepening of 24hpa over 24 hours is the definition for a "bomb low" or (more excitingly) an "explosive depression". More than 24hpa is required closer to the pole, and less closer to the equator. The ratio of sin(lat)/sin(60deg) is used to scale the 24hpa figure. So for 35deg latitude (as we have with this system) the required pressure drop is about 16hpa. So (assuming the modelling verifies) this system comfortably meets the criteria for a "bomb low".

[Razor]

Thought I'd create a separate thread for this one, could have some severe impacts on the region given its post Gabrielle fragility

[Blowy]

Possibly, however I reckon Gabby opened up all the congested waterways (tree, silt, shingle,fences), so this rainfall event can easily find its way to the sea, mainly, via clear channels. Pretty wild in Havelock North, some meaty dumps. Had 20mm here today, 45mm at altitude on coast (Waipoapoa). Looks like system spinning a little further south so worst to come? Gabby was 263mm overnight rapid dump event here in town.

[Kobi]

The GFS model has a 1006mb - 983mb change in 24 hours, so its just 1mb short of being classifiable as a weather bomb, the ECMWF has a change of 1007mb down to 985mb in 24 hours, which is just 2mb short of being classifiable, so it will be close if it actually becomes one or not, though knowing how the term is misused in our country, it wouldn’t surprise me if its called one anyways.

Bombogenesis, or more correctly explosive cyclogenesis, is latitude dependant. At 60degS a deepening of 24hpa over 24 hours is the definition for a "bomb low" or (more excitingly) an "explosive depression". More than 24hpa is required closer to the pole, and less closer to the equator. The ratio of sin(lat)/sin(60deg) is used to scale the 24hpa figure. So for 35deg latitude (as we have with this system) the required pressure drop is about 16hpa. So (assuming the modelling verifies) this system comfortably meets the criteria for a "bomb low".

Never knew that, thanks for the explanation!

[midgrove]

There is no such thing as a weather bomb - that term was coined and misused by the media.
New Zealand has gained a rather unfortunate reputation internationally for misusing weather terminology.
The official term is "bomb low" or "explosive cyclogenis.
I havnt heard MetService refer to "depressions"or "anticyclones" for years now

[TonyT]

I havnt heard MetService refer to "depressions"or "anticyclones" for years now

I still do

[Razor]

Fishing boat missing off Gisborne. Not good with this system.starting to wind up. Hope there is a successful search outcome

Really hope theres a positive outcome here, 2 people spotted in the water alive but now lost from sight. the conditions must be awful https://www.rnz.co.nz/news/national/520 ... ntact-lost

[Ash]

Yeah hats off to the people out searching.
Surf this weekend on the coast will be dreamy for the surfers.
Radar showing a big soaking incoming for Hawkes Bay.

[Razor]

Rain radar is pumping concerning amounts of heavy rain into the Hawkes Bay and Gisborne hill country. I don't think it's going to look good in the morning

[tornado]

Coastal Hastings under a state of emergency now.

[Kobi]

Gisborne has had 135mm between today and yesterday, with Tolaga bay having 115mm yesterday, though no data that i can find on whats fallen there today.

[Blowy]

Coastal Hastings is sea inundation. Only ~75mm so far for the event, and clouds lifting now.

[Achten]

Hastings south rural, sitting at 71.1mm from this event so far.

[Simon Culling]

This was posted at 7:30pm (GMT) our time here Tuesday (25th June) evening which I think is 7:30am NZ time on Weds 26th June. So these are probably 24 hour rainfall totals to 6am or 7am on your Wednesday morning from the Gisborne area:

218mm at Mangaheia
194mm at Hikawai River
190mm at Tokomaru Bay

From this NIWA tweet:

https://x.com/NiwaWeather/status/1805685907661766735

[Blowy]

Topped out at 100mm here in Havelock North for the event, maybe a bit more to come.

Noted on the Farming show today NIWA issues a heads up for mid July on, 'Tropics active', which *might* mean more severe weather for HB/EC.

We dont really need that! My question is, what sites do you guys look at for crystal ball gazing 14days+ out?

Thanks in advance from us EC farmers

[Ryza117]

Just over 130mm here in Patoka. Not as bad as expected, I think the bulk of it went to our north with more of a SE flow to it.

[Kobi]

Topped out at 100mm here in Havelock North for the event, maybe a bit more to come.

Noted on the Farming show today NIWA issues a heads up for mid July on, 'Tropics active', which *might* mean more severe weather for HB/EC.

We dont really need that! My question is, what sites do you guys look at for crystal ball gazing 14days+ out?

Thanks in advance from us EC farmers

I personally use the model viewing site Tropical tidbits to view models, specifically its southwestern pacific region, which has ECMWF up to 10 days out, and GFS up to 16 days out, though for a New Zealand specific look theres likely some better sites, though im not aware of any that are free to use.

The GFS also has an ensemble model (which is basically a bunch of different models for slightly different variations in data for the forecast) which can go like a month in advance, but not very accurate that far out.