Cook Strait Weather Bomb 2020.09.18?

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Cook Strait Weather Bomb 2020.09.18?

Unread post by Coopsy »

I was watching the Met Service Wellington Radar one hour animation ( an image every 7 minutes or so) this morning to try and determine how long it was going to be before this large cold front moved off us here in the Manawatu. Whilst watching the animation repeat I could see the main band of rain moving slowly from SW to NE. A couple of notable Cb's appeared briefly just off the Brothers Islands in Cook Strait, the first at 7.28 am and another one in the same spot 40 minutes later. Both were short lived. At the same time when I first observed this, the animation started at 7.21 am BTW, I noticed a convex arc moving north away from Wellington and running roughly west-east.

When I checked the earlier hourly radar images a good length of the arc had been a skinny row of Cb's around 6.00 am. As the main front moved from left to right this feature moved at right angles to that main flow and only dissolved as the front moved off. In the latter part before 9.43 am as more of the front moved south of Wellington, there appeared to be another shock wave at the bottom of the possible circle in a concave shape. Because I didn't see all of the images prior to 7.21 am I can't be certain if there weren't more large Cb's in the sounds. I understand that parts of Wellington had considerable downpours this morning.

The image attached is from the Met Services Wellington Radar at 7.28 am Sep 18th 2020. Has anyone come across this before? Could what appears to be a shockwave be related to those sudden Cb outbursts? I have seen something similar of satellite images a few years back. It may also be related to the arrival of the southerly undercutting the NW flow of the main front, which I feel is most likely as the temperature dropped nearly 8C from dawn to noon! I saved all of the 7 minute images from 7.21 to 9.43 am as well as a few of the hourly images back to 4.00 am.
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Re: Cook Strait Weather Bomb 2020.09.18?

Unread post by Awhituobs »

it may also be related to the arrival of the southerly undercutting the NW flow of the main front
i think you just answered your own Question :)
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Re: Cook Strait Weather Bomb 2020.09.18?

Unread post by Nev »

Coopsy wrote: Fri 18/09/2020 14:25 Cook Strait Weather Bomb 2020.09.18?
I don't think it was a 'weather bomb', at least not in the meteorological sense, i.e. to quote MetService
* A 'bomb' low is technically known as ‘explosive cyclogenesis’, and is defined as a low pressure system that deepens by at least 24hPa in 24 hours, with a small correction for latitude. Often in the media a weather system may be referred to as a ‘weather bomb’ when this criterion is far from being met.