Subtropical Low (Ex-TC June) 20-21 January

[David]

Time for a new thread on this subtropical low due to cross the North Island. Metservice forecasting heavy rain developing in Northland and Auckland on Monday 20th

Here is the GFS pressure forecast for 1pm Tuesday 21st.

[NZstorm]

Will be interesting to see the impacts on New Caledonia and Norfolk island over the weekend as it moves down this way.

Looking like the fronts will move too quickly to cause any flooding issues over the North Island. Perhaps the upper South Island will get more prolonged rainfall. Have to see how the low moves.

Also the threat of gales for northern NZ.

[Manukau heads obs]

sure looking good on the sat image now...undergoing rapid deepening

the models have it moving SE relatively fast....its the fast moving ones that in the past have brought damaging gales to northland
(i.e it weakens, but it gets that much closer by the time it does)

I wonder what effect the cooler than normal airmass coming up and around the top of the high in the tasman will have...might make it into a good rain maker?

[David]

GFS has been pretty consistent on 10-25mm rain for Waikato northwards, with more in the central NI and BOP. I'm hoping we get a little more than that though

[harleyb]

Sounds promising...

2. SOUTH PACIFIC AREA (WEST COAST OF SOUTH AMERICA TO 135 EAST):
A. TROPICAL CYCLONE SUMMARY: NONE.
B. TROPICAL DISTURBANCE SUMMARY:
(1) THE AREA OF CONVECTION PREVIOUSLY LOCATED NEAR 12.5S
160.8E, IS NOW LOCATED NEAR 13.8S 160.2E, APPROXIMATELY 625 NM
NORTHWEST OF NOUMEA, NEW CALEDONIA. ANIMATED INFRARED IMAGERY
DEPICTS A CONSOLIDATING LOW LEVEL CIRCULATION CENTER (LLCC) WITH
DEEPENING CONVECTION. A 160841Z TRMM 85GHZ MICROWAVE IMAGE SHOWS A
BROAD LLCC WITH FORMATIVE, ALBEIT BROKEN, CONVECTIVE BANDING ALONG
THE NORTHERN AND EASTERN SEMI-CIRCLE. UPPER LEVEL ANALYSIS REVEALS A
FAVORABLE ENVIRONMENT AS MULTI-DIRECTIONAL OUTFLOW IS BEING OFFSET
BY MODERATE TO LOW (10 TO 20 KNOTS) VERTICAL WIND SHEAR. SEA SURFACE
TEMPERATURES IN THE REGION ARE ALSO FAVORABLE FOR DEVELOPMENT.
DYNAMIC MODELS ARE AGGRESSIVELY DEVELOPING THIS SYSTEM AS IT DRIFTS
POLEWARD. MAXIMUM SUSTAINED SURFACE WINDS ARE ESTIMATED AT 15 TO 20
KNOTS. MINIMUM SEA LEVEL PRESSURE IS ESTIMATED TO BE NEAR 1006 MB.
DUE TO THE RECENT INCREASE IN STRUCTURE AND OVERALL FAVORABLE
ENVIRONMENT, THE POTENTIAL FOR THE DEVELOPMENT OF A SIGNIFICANT
TROPICAL CYCLONE WITHIN THE NEXT 24 HOURS IS UPGRADED TO MEDIUM.

[Nev]

Here's today's Severe Weather Outlook from MS for early next week. Although they have risks of heavy rain and gales from this Low (ex-TC ?) as low, I suspect they may increase in tomorrow's outlook…

MetService - Severe Weather Outlook

Issued: 2:11pm Friday 17 Jan 2014
Valid from Sunday 19 January 2014 to Wednesday 22 January 2014

A front is expected to move northwards over the South Island on Sunday and may stall over Westland. A burst of heavy rain is likely in the southwest of the South Island with this front, and in southern Westland and northern Fiordland there is a moderate confidence of warning amounts of rain on Sunday. Further north in Westland, there is a low confidence of rain reaching warning criteria on Sunday and into Monday. In the east of the South Island, the front is preceded by strong northwesterlies, and there is a low confidence of severe northwest gales about the Canterbury High Country and parts of Otago and Southland early Sunday.

Meanwhile, a ridge of high pressure over the North Island on Sunday should move eastwards on Monday as a low approaches from the north. The low is expected to cross the North Island on Tuesday, but there is still considerable uncertainty regarding the progression of the low. Rain is expected to gradually spread south in a northeast flow on Monday. There is a low confidence of heavy rain reaching warning criteria in Northland and Auckland on Monday and into Tuesday, with severe northeast gales possible. On Tuesday, rain is likely for much of the North Island. For the Coromandel Peninsula, Bay of Plenty, Taupo and the central North Island mountains, as well as Taranaki and the far north of Gisborne, there is a low confidence of rain reaching warning criteria.

As the low pulls away to the east later Tuesday and on Wednesday, southwesterlies should spread across the country, with gales possible in Auckland and Northland. The low confidence of severe gales in Northland and Auckland also covers the possibility of southwest gales becoming severe for a time on Tuesday.

MetService Severe WX Outlook map - Is. Jan 17, 2.11pm.png

[NZstorm]

Looks like the rain spreads onto Northland Monday pm and elsewhere by Tuesday.

GFS rainfall chart here for the event. The gfs will be underestimating rainfall for Northland to Bay of Plenty. Embedded instability and orographic enhancement should lead to locally bigger totals than shown.

The wettest spot still looks to be eastern BOP ranges where 150mm could fall.

[Nev]

Here's today's Severe Weather Outlook from MetService, with heavy rain and gale risks upgraded to moderate…

MetService - Severe Weather Outlook

Issued: 2:04pm Saturday 18 Jan 2014
Valid from Monday 20 January 2014 to Thursday 23 January 2014

A subtropical low (the remains of Tropical Cyclone June) is expected to approach the upper North Island late Monday, then cross over the North Island on Tuesday. At this stage, the low is not expected to be an extreme event, but is likely to bring a period of heavy rain to parts of the North Island and upper South Island from late Monday through to early Wednesday as it passes southeast.

There is a moderate confidence that rain may approach short duration warning amounts about Northland, Auckland, Coromandel Peninsula, Bay of Plenty,the central plateau, Taranaki, Wairarapa, Wellington and eastern parts of Marlborough from late Monday to early Wednesday as indicated.

In addition, a period of strong to gale northeasterlies are expected ahead of the low, tending southeast over the lower North Island, with a southwest change everywhere as the low moves away late Tuesday. There is a moderate confidence of northeast gales becoming severe for a time about parts of Northland and Auckland late Monday and early Tuesday, tending southwest late Tuesday with further gales expected. There is a moderate confidence of south to southeast gales about the lower North Island about Wellington, Kapiti, the Marlborough Sounds and Taranaki on Tuesday and early Wednesday.

A weak front is expected to move over the South Island on Wednesday behind this low, then the North Island on Thursday, with some rain about western places and strong westerlies about the lower South Island and lower North Island. There is a low confidence that westerly gales may become severe about coastal Southland and Clutha on Thursday.

MetService Severe WX Outlook map - Is. Jan 18, 2.04pm.png

[NZstorm]

Latest gfs shows we get some rain in Auckland from Monday morning. I'm hoping we can get 20mm in Auckland off this system.

[David]

I see GFS is still showing the rain band splitting either side of us!

[David]

Just cleaned up the rain gauge ahead of the rain tomorrow... lots of spider webs around the plates of the radiation shield but the spiders rarely build any webs inside the rain cone, thankfully.

The 00Z run of GFS has around 33mm for Auckland, up on previous estimates

[spwill]

I see Norfolk Island got 38.8mm, wind gusts up to 78km/h, current temp there is 24.2, dewpoint 22.7C.

The very humid air arrives here tomorrow evening.

[spwill]

Forecast dewpoints for tomorrow night

[NZstorm]

The 00Z run of GFS has around 33mm for Auckland, up on previous estimates

If we can get some embedded cuform that would help the rain total. Too warm for thunder though. 500mb -6C!

I would like enough rain to keep the garden good for another couple of weeks.

[Tornado Tim]

Too warm for thunder though. 500mb -6C!

Not quite, if you look at the Saturated Adiabatic Lapse rate, its borderline unstable on Tuesday afternoon. But borderline it is, so it may have a little lightning, might not. Low risk none the less.

[NZstorm]

GFS still plotting the heaviest precip to the west of the North Island. The strongest thermal gradient is there/warm front effect. I believe its known as a baroclinic zone and often see this with lows dropping from the north.

Latest total rainfall for the event from gfs.

[David]

Rain radar showing rain across the Auckland area, but no one seems to be recording any rain!?

Also, I see Metservice have issued a warning for SW gusting up to 120 km/h in exposed places of Northland and Auckland tomorrow morning.

[GraemeWi]

We have good steady rain here for the last 10 minutes (Henderson)

[NZ Thunderstorm Soc]

Also, I see MetService have issued a warning for SW gusting up to 120 km/h in exposed places of Northland and Auckland tomorrow morning.

This will really put Michael 'up on his toes'

[spwill]

Just light rain here, 18C, dewpoint 17C, calm conditions.

[jamie]

Well that seems to be the majority of the rain. 1.4mm for me. Compared to last year NIWA charts show my area to be at the same level today as we were last year. Scary thought given we have actually had cooler temps so less drying out.

[Manukau heads obs]

the rain is still coming
there will be high dew points with the center of the low
the sat image does not look like much rain,....but it will be...low cloud and low level rain...
should be anway...

[David]

I think we'll be lucky to get 15mm...

[spwill]

A freshening easterly here now, mostly dry brighter conditions , 21C, dp 17C.

[Manukau heads obs]

barometer down to nearly 1000hpa here already...
and yet the low center is supposed to be only 992?
must be deeper than that...