Squally showers with possible thunder, Upper NI 6th-7th May.

[Tornado Tim]

Wohoo CB's heading straight for us Northern North Islanders

Have a look at this loop
http://www.weatherzone.co.nz/satellite/

[Manukau heads obs]

and here
http://www.goes.noaa.gov/sohemi/sohemil ... mscol.html
there is a line of showers way to the north that are going to blow up as this new development (convergence) moves south
its not over thats for sure

[jamie]

good looking stuff

[Tornado Tim]

Some decent temps for this time of year 21-22°C with a high DP of 19°C around the Waikato.

relatively good sfc conditions

[spwill]

A mostly dry morning for Auckland with some sunshine, reached 22C. Currently overcast 20C dewpoint 18C.

Photo of shower cloud developing over east Auckland earlier today.

[David]

Warm here for May, reached 21C. Dewpoint max 19.4C, must be rare for the time of the year?
Not much interesting weather yet though.

[Tornado Tim]

Trough is right over the Manukau heads and over Northern Auckland dishing out some heavy showers.

Wonder what will come of it.....

[spwill]

Yes, that shower line has produced very little here but I see there has been a thunderstorm near the Waikato west coast on the line.

[David]

Gone really dull and gloomy here, looks like its about to pour but not much showing on radar.

[Paul Mallinson]

Yes, I see from home home that there have been some heavy showers moving through the Auckland area with a thunderstorm in the west in the last hour. There was also a thunderstorm earlier this afternoon at the southern end of the Kaipara Harbour.

The midday Whenuapai sounding was very unstable (as expected) along with very significant helicity (winds backing with height). One could expect convergence on the trough Brian was mentioning, in the Auckland area (northeast wind about 25kts at Whanagaparoa coming off the water meeting a lighter northery to the north side of the trough coming off the land) to kick something off.

It just shows you how one has to stick to the technical reasons why thunderstorms and possible tornadoes might form. Late morning/early this afternoon it didn't look like much was going to happen and it would be easy to give up on the threat scenario we had advertised. But when you have good technical reasons for doing so, then you are able to stick with your thinking.

Cheers,

Paul

[Tornado Tim]

For Reference here is the midday sounding from Whenuapai as Paul was mentioning.

Have a look at the wind flags

Hardly any Negative CAPE (convective inhibition)

[Manukau heads obs]

we did hear thunder at around 3:30
on the way to coromandel the mama on sunset from the cloud sheet moving in from the east looked nice

[NZstorm]

The cap on the NZWP sounding is the reason why I was a bit negative on our TS chances today.

Not a bad day in Auckland with mild conditions, which is not unusual in May.

[Paul Mallinson]

There was no significant cap. A temperature around 20C and a dewpoint around 18C allowed this sounding to convect with the CAPE up somewhere around 1150 J/Kg from memory. What was lacking was good upper support (from a short wave trough) and strong enough surface convergence in the face of non summertime (weak) surface heating to trigger the convection. There was some triggering since there were heavy showers around and the odd thunderstorm.
Besides, how could you know that that noon sounding would have some sort of capping without using a forecast sounding from a high resolution numerical model. Ours didn't show that.

[NZstorm]

Besides, how could you know that that noon sounding would have some sort of capping without using a forecast sounding from a high resolution numerical model. Ours didn't show that.

The cap was observed on the 12z gfs. I plot my own skew-t soundings but don't save them after use. But you can see the cap on the sounding that Tim posted. The cap is small but this is significant in May. I also noticed the lack of upper level support as well. Also, I tend to lift the parcel off the 950mb dewpoint, its a conservative way of estimating CAPE and I believe it gives a better picture of the instability rather than the surface dewpoint.

[Tornado Tim]

Some strikes being picked just off Doubtless bay Northland, looks like an intensifying line.

[NZstorm]

Yes, the next trough line making its appearance. It gradually comes south overnight no doubt with some rumbles, more likely in the west.

[David]

Looks like it's giving Kerikeri a good downpour - up to 37mm there for the day

[spwill]

Yes, currently thundery over the top of Northland.
Kaitaia on 13.6C, Whangarei on 17C.

Kerikeri is showing 27.4mm on the latest Metservice hourly observation.

[spwill]

25mm at Greylynn from a crop of heavy showers in the early hrs, brought in a change of air, now 13C.

[jamie]

Wow what a sudden change of air over night. Temp graph is like a cliff face at the change of air

[iomkiwi]

Just had a pretty intense squall come thru here - went from calm to almost 64km/h in very quick time, heavy rain at the same time, pretty sure there was some hail in there too.
Max rain rate was 160.8mm/hr at 6:56am
Max gust 63.7km/h at 6:55am from the North - the wind for the previous few hours was from the East.
120 min average is calm

squall.png

squall2.png

[David]

25mm at Greylynn from a crop of heavy showers in the early hrs

Almost double what Howick got - 13mm here

[NZstorm]

We had very heavy rain here for about an hour this morning and I'm quite sure more fell here than at Rickys. I have to get a rain gauge set up.

[Nev]

Yeah, quite heavy 22mm here in the wee-smalls - almost blue dome skies this morn though.