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Ex-TC Gita 19th February 2018

Gita--Satellite-1600-19-Feb-sm

There's much excitement in the air at the moment! First off this is the first Weather blog on the NZ Weather Enthusiasts site. It's also my first blog, and my first blog about a weather event. And it's a significant weather event I'm blogging about.

I've been watching TC Gita for several days - right from it's formation in the tropics. Even at that point there was talk of it impacting New Zealand in some way, although no-one at that point knew how of course. So the purpose of this blog is to document the passage of (now) Cyclone Gita as it passes across the country. Feel free to add your comments below, ask questions, and tell me how things are going for you. You will need to log onto the site to do so.

 Oh - by the way, the cover image is of Cyclone Gita taken at 1600 hours NZDT on 19th February. The eye is clearly visible top left.

Right lets get started:

Monday 19th Feb 2018 8:00pm NZDT

Gita is currently 935km WNW  of Cape Reinga with a central pressure of 986mb 

Pressure 2000 19 Febv2

  (Image Source: Windy.tv)

 

The proposed track according to the latest ECMWF model is from points 1 to 2. It's expected that as the cyclone moves south it will deepen to around 975mb before reaching the Nelson Buller regions. The GFS model suggests a similar path, although slightly further south. 

Model runs through the day have pushed the impact point north, and then south again, so there is still some variability in the proposed path. The centre of Cyclone Gita is expected to hit the top of the South Island sometime around 7pm on Tuesday 20th February.

As the cyclone moves south it will be affected by winds from the south at high level - effectively causing shear across the system which will ultimately lead to it's demise. Although the cyclone will transition quickly across the country, it's what is going on around the centre that is interesting.

Expected rainfall

Cyclone Gita currently holds alot of moisture. Using the ECMWF model again you can see that rainfall is largely confined to the lower left quarter of the cyclone. That said there is a long "tail" spinning out of Gita, and this precedes the core of the storm (ie it points in the direction the storm is moving.)

This will bring rain to lower parts of the North Island from about midnight tonight, and heavy rain in the Wellington region from about 9am tomorrow.  A warning is currently in place for that region - expect 100 to 120mm in the 24 hours from 1:00am Tuesday to 1:00am Wednesday. Other areas likely to be affected are the Marlborough Sounds, Buller, Westland, and the Canterbury foothills, and warnings are out for these areas. Check out Metservice.com for the latest details. Snow is expected to fall on the higher Southern Alps to about 900m, as the bottom of the cyclone sucks up cooler air  from the South, and pulls it onto the the country from an easterly direction.

Expected wind

The image below shows the ECMWF Forecasted model 24 hours from now. The core of Gita has just transitioned across the top of the South Island. Again, this is a forecasted view so is subject to change.

Pressure 2100 20 Feb ECMWF 

(Image Source: Windy.com)

 There are several interesting features here. What remains of the cyclone centre now sits off Kaikoura. Strong south to south east  winds of up to 42 knots are being pushed up into the Marlborough coastline. Meanwhile the area between New Plymouth and Wellington continues to get a battering with NW's between 55 and 75 km/h. Gusts in the Wellington area could reach 120 km/h.

 Overall the storm moves off the country very quickly and by 7am Wednesday 21st February, it is expected most of the severe impacts will have occurred. 

So we wait and see what happens. I'll update this blog over the next few days as the models are updated. Again if you have any feedback then feel free to post it below in the comments section

Tuesday 20th February 0900

Gita now has it's own wiki entry. You can find that here: https://en.wikipedia.org/wiki/Cyclone_Gita

Rain started falling a little earlier than predicted in Wellington last night, and has continued steadily throughout the night. At this stage there is little to no wind associated with it, but that is expected to change this afternoon. Onto the models.

Both GFS and ECMWF models were updated last night, and now largely say the same thing.The centre of  Gita is expected to directly impact the top of the South Island just after 9pm tonight with a central pressure of around 982mb.It will quickly transition across the island towards Kaikoura, and by 2am the centre will lie off the Kaikoura coast.

Expected Rainfall

Heavy rain is currently affecting Nelson and Tasman Bay regions. This transitions across into Marlborough early this afternoon. The bulk of the rain will fall along the West Coast from 7pm tonight

Expected Wind

For the Wellington region, the forecast remains the same - strong winds building tonight up to 120km/h gusts. On average NW's 55 to 75km/h. These will slowly ease during Wednesday. 

Tuesday 20th February 1930

No model updates as yet, so just some regional updates. 

Wellington

It's been calm all day, but wind finally kicked in from the NW about 7pm. We're still expecting stong NW's to kick in tonight, (Strong wind warning in place).50mm of rain has fallen since midnight so far, but their have been regional variations. Wainuiomata has had 74mm today already. By all accounts the weather we've seen is fairly typical of what's happened in other areas where the wind has already hit. It truly is the calm before the storm. Air New Zealand flights were cancelled from 2:45pm at wellington airport.

Air pressure has dropped significantly as Gita has moved closer. The following graph shows barometric pressure from midnight this morning at the Maungaraki weather station:

Air pressure 1833 200218

 Wind is picking up from the NW

Nelson Region - Motueka and Riwaka 

State of emergency declared. Flooding. Evacuations are taking place in Riwaka

Buller and Westland Region

State of Emergency declared. This allows the Defence Force to head up the road north of Greymouth, and warn people to stay put.  Roads north and South of Hokitika closed. This is the same area that was hit about  a month ago from ex TC Fehi.

Canterbury Region

Christchurch: State of emergency declared. Heathcote river likely to burst it's banks tonight and residents are being asked to move to higher ground. Concern over Banks Peninsula which will bear the brunt of the storm tonight.

Selwyn District: State of emergency declared. Concerns that the Selwyn River may flood overnight, and this will mean evacuations of low lying areas.

 Wednesday 21st February 0700

The depression that was Gita, has now passed over New Zealand, it's energy now represented by two low pressure centres. The depression on the right hand side will continue to move off the coast of New Zealand, while the one on the left will stay around a little bit longer, moving upwards towards the central North Island. Luckily this one has significantly less energy than ex TC Gita. Winds will tend southerly across the country as a whole.

An interesting point is that the depression on the left has a slightly lower central pressure than was predicted. This means that more energy has been retained within this depression than the one on the right hand side of the South Island, which translates into less severe weather than predicted for the Kaikoura Coast and Canterbury.

Pressure 2000 21 Feb (Image Source: Windy.com)

Regional Updates:

Wellington Region

SH1 Closed - coast road has been inundated with waves of up to 6m. Will need repairing, before reopening.

Taranaki Region

State of Emergency declared. Power has been out to about 15000 homes for the last 24 hours or so, and winds need to die down before repairs can be made.

Wednesday 21st February 2000

Time for a wrap up. Locally the following measurements were taken from the Huttweather.co.nz station in Maungaraki:

  • Total rainfall for storm = 86mm
  • Maximum gust = 46km/h
  • Average wind speed = 46km/h
  • Minimum pressure = 988mb

There's a few good places that provide a summary of the impacts from this storm. The following links will give you more information:

The MetService have also produced an informative video

If you have any comments about this blog, please let me know in the comments section below, even if you just want to let me know you've enjoyed reading it! Remember the purpose of this blog section is to record weather events for the purposes of learning from historical events, so if something is missing, please let me know.

Do not rely on this information for the protection of life or property. Please ensure you keep up to date with any warnings and watches issued by the New Zealand MetService, as the MetService is New Zealands official weather forecast provider.

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