NZ Weather Forum

very squally shower line moving through here now

59 kts squalls here just now
(109kmh)

Sun is shining now but a blustery WNW has suddenly roared in, gusting around 50 km/h. Feels like winter today.

Westerly gusts in the Waitemata currently up to 93 km/h (50 kt)..

Re last night, according to the Bay of Plenty Times, Mt Maunganui Intermediate's own weather station recorded gusts to 173 km/h.

I did post on M/S FB page that they need to increase the auckland marine forecast....
I wonder what weather station type they have?

Thunder heard in Hamilton just now.

From seeing the damage to the stadium, im not surprised by the 173km/h gust.

There's been a few reports of 'mini-tornadoes' around the BoP this arvo, including at Tauranga Girls College. Pretty sure they're all just squalls through. No doubt because it seems our ignorant journalists have recently slipped back into their old habits of using the 'm-word' again. So any old squall, etc again gets referred to as a 'miniture-tornado'.

Yes just squalls yesterday. Westerly change roared through at 12 and killed off any potential action later. Must have dropped 5 deg as well.

Very doubtful it was a tornado, I can't see any rotational damage, also it was very localised, wind would be quite funnelled to a point in there too.

The fact its such a narrow path points to a tornado
as does eye witness accounts of sudden freight train like sound then gone again just as fast

Need directional low level flow for a tornado and very moist air. Having a quick look back, both looked lacking with that front which points to a wind gust. But with the weather you can never be sure.

I was looking at weather data for the wrong day (Friday).

Thursday had a moist NE flow so a small tornado could have occurred. I generally say tornadoes as the low instability numbers in these types of events would still favour a tornado. Microbursts tend to be more likely when the CAPE is high.

There was a general upper level NNW
wind and a surface NE wibd
add to that the whole coastline and ranges effects in the area...

I've yet to see a wind gust leave such a long, narrow and selective trail of destruction. Although I wouldn't rule out a micro-burst, all the evidence tends to suggest a waterspout turned tornado to me. This trail of damage reportedly extended from Clyde St to Te Maunga (Baypark Stadium), a distance of about 4.6 km. Most of these reports come from Clyde St, Waitui Grove, Golf Rd, Lodge Ave, Ascot Place, Links Ave, Epsom Rd, Golf Rd, Maunganui Rd, Owens Place and Baypark Stadium. Those reporting the damage have also said neighbours just tens of metres away remained relatively unscathed. I've put together a damage track-map based on the dozens of reports I've trawled through so far…
I'd imagine that the Baypark Stadium, built in 2000, would have to have had a wind-rating of at least 200 km/h, even though the canopy-structure did look a little light-weight. If the stadium, which holds about 20,000, had been in use that night, I think we'd have likely seen multiple injuries and even possible fatalities from all the flying debris.

I read one report of a car and driver being picked up and spun around 360 degrees. However, one of the more interesting eye-witness accounts I've read recently was this one…

'Panel beater's work takes a beating' - BoP Times

All points to a tornado to me. Interesting tornado path when you consider the radar image and the direction of the cell movement. I was expecting a more west to east track.

I managed to cache a few radar-images from around that time. The spiralling front did generally move across from west to east, but the wind and rain was being pulled down from the NW.

thanks Nev for the info on damage path etc
and eye witness stories etc
my thinking is this would have been a fast moving nado...the CB's were moving fast that day....you could tell by the rain radar things were moving through very fast...
even though the surface winds were not very fast.....it could have had a forward speed of 100kmh......and so alot of the damage would have been on one side only..making it look like straight line wind damage

Need directional low level flow for a tornado and very moist air. Having a quick look back, both looked lacking with that front which points to a wind gust. But with the weather you can never be sure.

I was looking at weather data for the wrong day (Friday).

Thursday had a moist NE flow so a small tornado could have occurred. I generally say tornadoes as the low instability numbers in these types of events would still favour a tornado. Microbursts tend to be more likely when the CAPE is high.

Manukau heads obs wrote:thanks Nev for the info on damage path etc
and eye witness stories etc
my thinking is this would have been a fast moving nado...the CB's were moving fast that day....you could tell by the rain radar things were moving through very fast...
even though the surface winds were not very fast.....it could have had a forward speed of 100kmh......and so alot of the damage would have been on one side only..making it look like straight line wind damage

Yes, agree Brian. If say its forward speed and rotational speed were both say 100 km/h, they would effectively cancel each other out on the side with backward facing winds (relative to a point on the ground), while doubling to 200 km/h on the side with forward facing winds. Then again, even if its forward speed was say only 50 km/h, but its rotational wind-speed was say 150 km/h, then the side with backward facing winds would reduce to 100 km/h, while the other side with forward facing winds would also increase to 200 km/h.


I had a chat with Mt Maunganui Intermediate's science teacher last week. Their 3-month-old, all-in-one weather station is called a 'Professional Wireless Weather Station - XC0369 ', and was very well secured to the roof of their admin building by the caretaker...
The actual reading was 172.3 km/h and, from the considerable damage the school sustained, looks to have been right in the path of the apparent tornado. They have since discovered that the roofs of 2 classroom blocks (8 classrooms in total) actually lifted then came back down. Sunshades in front of the damaged classrooms were destroyed and the stainless steel poles supporting the sunshades, which were set in concrete, were bent. A trampoline was also embedded in the office block window and another trampoline was wrapped around a concrete column in front of the office block...
She also said the damage to roofs on houses around the school was incredible, with 11 of their families affected. The media reported that 8 homes had to be evacuated that night, and last Tuesday said that at least 70 claims had been lodged to NZ's biggest house and contents insurers.

Btw, going by this rather amusing little blog, the width the apparent tornado's damage may have been wider than indicated on my track-map.

Here's another story about the previously mentioned waterspout and possible tornado in the Far North also on May 14…

'Water spouts and mini-tornadoes' - The Northland Age

Although there appears to be a slight difference between the waterspout sighting and the damage report across the bay, I've included the 2pm radar image and a map for reference…

Nev wrote: I had a chat with Mt Maunganui Intermediate's science teacher last week. Their 3-month-old, all-in-one weather station is called a 'Professional Wireless Weather Station - XC0369 ', and was very well secured to the roof of their admin building by the caretaker...

Mt Maunganui Intermediate WS.png

The actual reading was 172.3 km/h and, from the considerable damage the school sustained, looks to have been right in the path of the apparent tornado.

Not that I am disputing that this could be a tornado or not, but the Reading reported by the supposed Weather Station is outside of its recordable range of 0-100km/hr according to specifications in the link provided: Another thing to note with the wireless transmission times of those typical "Professional" Weather stations, can breach 1 min instantaneous, which is far too coarse to record such a fast evolving event. The wireless transmission interval isnt listed on the link, so I cant confirm on that, but previous predecessors of similar types of Weather stations are very slack when it comes to transmission times.

this new station type I think has 5 second transmission rate?

Hmm… In the link I provided it says 'wind speed: 0-100 mph' (not km/h), although it doesn't give a range for 'wind gust'. Going by the manual, I think they're talking about an accuracy-range, rather than not giving readings past 100 mph (160 km/h). I am aware that most WS's tend to become less accurate in extreme winds. However, 172 km/h is certainly consistent (or at least in the same ball-park) with the damage reported. The manual also says that the measuring interval of the outdoor sensor is 16 seconds.

It's also entirely possible that each transmission from the outdoor sensor contains a minimum, average and maximum for each period, meaning the reading could be quite accurate. It's unfortunate better detail is not provided so you know.