Update from Weatherwatch.co.nz

Tropical Cyclone Lusi has been named today by the Fiji Met Service and currently lies over Vanuatu as a category 1 tropical storm.

Winds are sustained at gale force.

Forecasters expect Lusi to grow into a Cat 3 or 4 cyclone before being technically downgraded before reaching New Zealand waters this Friday/weekend. While the storm will likely lose it's cyclone status before arriving here, it may well still retain Cat 1 or 2 strength.

The exact path of the centre of Lusi is unknown at this early stage for New Zealand but the centre could cross anywhere from Northland to just east of the North Island over the weekend.

With tropical cyclones the severe weather is near the centre - so until we can lock in exactly where the centre will track it makes it hard to pinpoint severe weather risks in NZ.  However generally speaking heavy rain could affect northern and eastern areas and severe gales could affect a number of North Island regions




Above / Saturday morning / ECMWF
Below / Saturday morning / MetOcean

http://metvuw.com/forecast/forecast1.php?type=rain&region=nzni&tim=102

looks like a wet and windy weekend ahead for Kiwiland.

Update from weatherwatch.co.nz 8.00am

Lusi is now classed as a severe tropical cyclone after reaching the predicted category 3 status overnight according to both JTWC and Fiji Met.

The storm will now travel over open waters towards New Zealand, but will start to weaken before arriving in the upper North Island over the weekend.

Winds are sustained at 120km/h with gusts to 150km/h according to JTWC.

Fiji Met Service says Lusi is expected to intensify further today.

Despite it now being just 48hours out from arriving in northern New Zealand computer models still haven't locked in an exact track for the centre of the low.  Various computer models agree the centre of the storm will likely approach Northland on Saturday, they then start to disagree about what happens next.

For example one model tracks Lusi's remains directly down the North Island while another suggests it will slide down the western side of New Zealand - something that doesn't happen too often.

"This might sound like we're splitting hairs but the difference between the center of this low tracking 100kms further west or east can have profound differences to the severe weather over land in New Zealand" says head weather analyst Philip Duncan.

Yesterday New Zealand's Ministry of Civil Defence & Emergency Management out of Wellington - which operates under Metservice advice - also launched warnings for the nation, saying this cyclone would likely "track over northern New Zealand on Saturday and Sunday and then track southwards over central New Zealand before moving out to sea east of the South Island on Monday" - which mirrors a similar forecast track by WeatherWatch.co.nz.

MetService says Lusi has the potential to be a "significant event".

WeatherWatch.co.nz maintains that damage is expected for some parts of New Zealand but that forecast needs to be balanced with the fact that larger areas will not be damaged too. 




Metservice

Updated 3:55pm from Weather Watch. Is she changing direction?

The exact path of Lusi over New Zealand this weekend remains unclear with computer modelling continually shifting the future track of the storm westwards.

This afternoon Lusi's wind speeds have ramped up further, according to JTWC, with winds averaging 130km/h and gusting to 160km/h.

Fiji Met says the air pressure has now fallen to 960hPa.

In the past 24 hours most reliable data has suggested the centre of the tropical low might now push west of Northland and Auckland on Saturday night/Sunday morning.

The latest data also suggests the centre of the low might track further south into the South Island now - bringing more rain and wind into the upper South Island and potentially Canterbury.

"For the working week so far the data has suggested the low would track across the North Island or along the western coastline of the North Island. Today we're seeing the high east of New Zealand pushing back a bit - helping the low sink further southwards down the South Island" says head weather analyst Philip Duncan.

"We'll need to see another 12 to 24 hours of computer runs to be certain of this developing change in the predicted track".

Mr Duncan says the high east of New Zealand is acting as leverage - helping tilt the air pressure and that shifts the direction of the low. 

WeatherWatch.co.nz says the shift in tracking will still see Northland, Auckland, Coromandel and Waikato exposed to the full brunt of the storm - which will be weakening upon arrival.  Two data updates today have weakened the low a little upon arrival - however there would need to be further similar updates before that could be locked in. 

However Fiji Met has today release a new threat map which shows the storm retaining Cat 2 status all the way to the South Island - something rarely seen.

Many farmers are wanting the rain to arrive with near-drought conditions forming in some North Isand areas.  To have the low weaken before landfall would be a positive outcome, reducing wind damage risks but still maintaining soaking rains for many areas.

In Auckland winds are likely to ramp up as Saturday ticks along.  Gales are expected to develop with the risk of severe gales in the afternoon or evening - and overnight.  If the low tracks further west than predicted it may not mean any easing in winds - instead it will change the wind direction away from ESE to more NE.

Rain may also be patchy - although patchy doesn't mean light and drizzly.  Some rain data suggests torrential downpours in the mix with lighter falls. 

"My feeling is that this low is quite complex and we may not have a truly clear picture until Saturday, at least rainwise"

The geography across the country means the wind and rain could be severe in a number of places.  "Everytime the models shift the track of the low it means all the forecasts also change - especially wind direction, which is key to working out severe gales and where highest rainfall accumulations will be".

With the low now possibly tracking further south over the South Island places like Dunedin may now have more wind and rain - along with Canterbury, Nelson and Marlborough.

"Originally it looked as though the low would take the offramp at Cook Strait to depart our shores, now it looks as though it might turn off further down the road over Canterbury and Otago".

Mr Duncan says the best advice to people is that this weekend, for many parts of the country, there will be wet and windy weather for a time "Not everyone will have severe weather or damage - but this storm is complicated and brings with it high risks for severe weather to various parts of the country".

Cyclone Lusi has moved out of the tropics and is now approaching northern New Zealand.

Lusi, currently a Category 2 tropical cyclone is lying about 800 kilometres north of Cape Reinga. Lusi's speed of movement is about 35 kilometres per  hour, and on its current track is expected to pass just to the northwest of  North Cape around midday Saturday bringing widespread heavy rain and easterly gales to the North Island from tonight (Friday night), and the upper South Island during Saturday. Rain is forecast to become heavy in Northland this evening, and 80-100mm are likely to have accumulated there by Saturday afternoon. The rain should spread quickly southwards, totalling more than 100mm in Coromandel, Bay of Plenty and Gisborne by Sunday morning.

Easterly gales will accompany the heavy rain, with severe gusts of 120km/h in Northland, Auckland and Coromandel Peninsula, and 130km/h west of the Kaimai Range.
Metservice.

Quite a significant change in track from the beginning of the week..

A very cool digital generated Pacific map of the wind and rain patterns is here...

http://earth.nullschool.net/#current/wind/surface/level/orthographic=-184.92,-34.12,640

You can grab it with your mouse and move the globe around.  Fascinating.


Wind Map Sth Pacific Luci 150314 by suthg, on Flickr