'Bomb' low crossing North Island Saturday 3 March

[Manukau heads obs]

Met Service has issued the first warnings now
severe gales for central and southern NI, gusts to 150kmh!

[TonyT]

Good morning all
Weather bomb is a term we don't use lightly

As I've said before on this forum, "weather bomb" isnt even a technical term at all. I believe its origin can be traced back to a quote (which may even have been a misquote) from Bob McDavitt. The actual term used by the authors of the original paper (Sanders and Gyakum, 1980 see here http://journals.ametsoc.org/doi/abs/10. ... .0.CO%3B2) which I read back in 1981 soon after it was published was "bomb cyclone" or "bomb low". At the time the McDavitt quote first appeared I thought that perhaps Bob had mis-remembered the term, or the reporter had misquoted, it, or maybe Bob did decide to coin the term "weather bomb" deliberately.

That paper also defined "explosive cyclogenesis" for the first time, which is also a good word to use for these systems as it conveys some sense of the dynamics of the system - ie what makes these systems so hazardous is not their size or their depth (central pressure) but the rate at which the central pressure is dropping, in the same way that the truly impressive thing about a seriously fast car is not the top speed it reaches, but the acceleration it has to get there.

[David]

Met Service has issued the first warnings now
severe gales for central and southern NI, gusts to 150kmh!

I'm a bit surprised Waikato has a warning but not Auckland, I wouldn't mind breaking my high wind gust record

[Manukau heads obs]

the auckland area will get hit hard too,dont you worry, thats my prediction
especialy if the low crosses the center of the NI
due to the wind flow being blocked by ranges, etc, it will want to find an easier route, which is through the narrow auckland region

[Manukau heads obs]

M/S have a watch in place for severe gale SW winds on saturday for northland and auckland now

[spike_01]

150 kph gusts here.. Bound to some damage..

[Nev]

As I've said before on this forum, "weather bomb" isnt even a technical term at all. I believe its origin can be traced back to a quote (which may even have been a misquote) from Bob McDavitt. The actual term used by the authors of the original paper (Sanders and Gyakum, 1980 see here http://journals.ametsoc.org/doi/abs/10. ... .0.CO%3B2) which I read back in 1981 soon after it was published was "bomb cyclone" or "bomb low". At the time the McDavitt quote first appeared I thought that perhaps Bob had mis-remembered the term, or the reporter had misquoted, it, or maybe Bob did decide to coin the term "weather bomb" deliberately.

That paper also defined "explosive cyclogenesis" for the first time, which is also a good word to use for these systems as it conveys some sense of the dynamics of the system - ie what makes these systems so hazardous is not their size or their depth (central pressure) but the rate at which the central pressure is dropping, in the same way that the truly impressive thing about a seriously fast car is not the top speed it reaches, but the acceleration it has to get there.

Hmm... Clicking on that link, I just get 'The requested article is not currently available on this site'?

May have even been Erick Brenstrum who popularised the term 'bomb' here in a National Geographic story about 20 years ago, according to this 16 minute Radio NZ interview back in August, 2008 (fast forward 11 minutes).

[TonyT]

Try this, you can only see the abstract, I think the rest is behind a paywall.

http://journals.ametsoc.org/doi/abs/10. ... 2.0.CO%3B2

[Philip Duncan]

Hey Tony - yes I'm aware that technically the term isn't "weather bomb" - that term is simply jargon for bombogenesis - but Bob made it far more user friendly for the public and media.

[TonyT]

I've deleted a couple of posts which did not help further the discussion of the subject at hand. Please stay on topic, and if you wish to debate adversarially with other forum members take it to PMs.

[Manukau heads obs]

Barometer starting to fall here already
its not much to look at on the sat image at the moment
I guess the jet stream is hiding it
talked to someone who flew from melbourne to auckland...really bumpy flight!

[littleheaven]

My weather station has the pressure down 1.8 hPa since 10am - when are we likely to see the rapid descent which could give it "weather bomb" status? (a term I really like, by the way, regardless of its technical validity )

Edited to add: Snap, Brian!

[borris89]

Flying into Wellington at 10.30am tomorrow morning, suppose the airport will close with gusts to 150kph??

[Manukau heads obs]

Taranaki will see the biggest pressure drop.....
the strong winds will be associated with the big pressure drop
thats expected to be overnight
you can see the jet stream is starting to kink in the tasman sea now
so thats the start of the cyclogensis
the thing about this system is its going to peak right over the NI
often system peak before they reach NZ...

[Manukau heads obs]

picture of where I think the low center is now
which if its moving east, has it crossing North Taranaki

[dan]

Forecast:
*** STORM WARNING IN FORCE ***
Westerly 15 knots. Tending northerly 25 knots this evening, then rising to 50 knots overnight. Changing westerly 70 knots but 45 knots north of Raglan Harbour early morning,easing to southwest 45 knots everywhere Saturday afternoon, then easing to southwest 30 knots Saturday night. Sea becoming Phenomenal in the south for a time. Northwest swell rising to 5 metres for a time.Southwest swell rising to 4 metres. Poor visibility in rain developing this afternoon,very poor visibility for a time overnight,then poor visibility in showers Saturday.

Haven't seen this before! Seas becoming "phenomenal"

[Manukau heads obs]

WOW
70 knot westerly expected for southern Raglan marine area?
thats insane
thats average windspeeds
never seen that forecasted before!

[littleheaven]

Haven't seen this before! Seas becoming "phenomenal"

Another fantastic term! I must say I've never seen it on a forecast either.

Barometer still dropping here.

[spwill]

Haven't seen this before! Seas becoming "phenomenal"

I recall seeing this in the marine forecast for Cyclone Fergus in 1996, I think it means sea swell 14m ond over.

[Manukau heads obs]

sea waves I think you mean
as there is not time for the actual swell to reach that height (the swell forecast is only 5 m)

i.e short period waves (i.e like chop) on top of the ground swell.....accentuating the existing swell that is there....which can make waves as big as 14m (i.e an individual wave and not a group of swells)

[littleheaven]

I recall seeing this in the marine forecast for Cyclone Fergus in 1996, I think it means sea swell 14m ond over.

Ah, yes, Wiki agrees. It appears to be the highest rating in the WMO Sea State Code. You learn something new every day.

[Tornado Tim]

I will most likely stare at my weather station when the wind gets going

I see that Metservice are expecting the low's central pressure to drop to 970hpa! Havnt had a low that deep for a while.....

[NZ Thunderstorm Soc]

I see that Metservice are expecting the low's central pressure to drop to 970hpa! Havnt had a low that deep for a while.....

Well not over the NorthIsland, except for a few close TC's moving past.
Shame we will miss the action down here, but then after the non-weather related natural events of the past 2 years , we don't really need a storm like that to come through. I hope there will no deaths or serious injury.

[Chris Raine]

Not sure if we are getting spillover rain here or a southerly flick but it has been raining intermittently since lunchtime

[Storm Struck]

Last night and todays model runs have brought the low slightly further south, which means top of the south and perhaps even down to into Canterbury will get some brief nasty weather from it.
Persistant rain from early morning with gale SE winds maybe around 70-80kmh in exposed places, always hit and miss with these type of systems sometimes they track away from where models depict so the next 24 hours will be interesting.
Wesport will be a place to watch for again 150kmh plus gusts, i remember a simular system location few years ago in february giving the northern west coast a battering.
It is bomb status so to speak but i think its over rated in terms of how its being put across from the media, 970hpa is deep but we have seen deeper in the past.
There is a fine line between warning the public over a wide area and being calm about the situation as it happens, but i guess as government forecaster you have to cover all basis and protect or warn the public the best you can.