February 2022 - South Island West Coast Rainfall event

4 minutes reading time (895 words)
A significant weather event is forecast to occur in Westland and Buller over the next few days. Westport itself was hit by a weather event that cuased significant flooding and damage in July 2021 and many residents are still rebuilding from this storm. This event is expected to be larger.
 

Setup

 
As you can see from the image above, moist air is being fed from the tropics and pushed onto the West Coast of the South Island. This is expected to occur for the next two to three days. 
 

Warnings

The MetService has published a Red Warning for this event. Red Warnings are only issues in frequently and where significant impact is expected from weather conditions. At 02 Feb 2022 2030 the following warning had been issued
NOTE THAT THIS IS NOT A CURRENT WARNING. OFFICIAL WARNINGS CAN ONLY BE ISSUED BY THE METSERVICE. FOR THE LATEST WATCHES AND WARNINGS PLEASE REFER TO THIS PAGE
 
 

Places to watch:

Cropp River (Hokitika River Gorge). This is traditionally New Zealands wettest place: https://data.wcrc.govt.nz/cgi-bin/hydwebserver.cgi/sites/details?site=81&treecatchment=3
 
 

Update 03 Feb 6:00pm

Westport so far seems to have escaped much of the planned rainfall. More rainfall is expected to fall though in this multi day event.
 
In the past 24 hours
 
 
The tropical flow that was coming from the tropical area to the North East of Australia, is now no longer as pronounced as it was yesterday. Much of the moisture associated with this flow is now being merged into a low pressure which is also being fed with cooler air from the south. With the cooler area mixing with the warmer air, rainfall is created and we can see this on the diagram in the top left.
 
The other tropical flow that was evident on yesterdays image, still exists, and that is driving the rain into the Nelson, Tasman and Buller regions
 
The high pressure to the right remains where it is, which will push the low pressure back down onto the West Coast on Friday afternoon. 
 
An Incoming high pressure that curently sits below Tasmania will eventually push the rain band up into the lower North Island on Sunday and Monday
 
A Red Warning: Heavy Rain  is still in place for the Ranges in Buller with between 250 to 350mm of rainfall to occur on what has already fallen at the coast. 
 

4th February 2022 8:30pm

The setup tonight remains similar to what it was last night. Cold air flows in from the south, mixing with warm moist air from the north. Temperatures reamin warm on the north side of the system. The temperature in Napier currently (9pm) is 27C! While on the Southern side of the system, temperatures are much colder - between 11C and 14C on the east coast of the south island.
 
The rain slowly moves north overnight, with an orange warning now in place for Wellington and Marlborough (100 to 120mm over 24 hours, at times with a rate of 10 to 20mm per hour).
 
There have been several evacuations in and around Westport today (Refer news articles below)
The Image below shows the period from around midnight on 4th Feb to the evening of Monday 7th Feb. The model used is the ECMWF model:
 
 
 
 

5th February 2022 8:30pm

The storm continues to move slowy north. 93mm of rainfall has been recorded today in Lower Hutt (an additional 8mm yesterday).
 
 
There are no Red Heavy rain warnings currently in place.  Orange heavy rain warnings still remain in place as follows.
 NOTE THAT THIS IS NOT A CURRENT WARNING. OFFICIAL WARNINGS CAN ONLY BE ISSUED BY THE METSERVICE. FOR THE LATEST WATCHES AND WARNINGS PLEASE REFER TO THIS PAGE
 
Niwa (@niwa_nz ) have published an infographic that allows you to see where the rain fell from this event:
 
 

 

Media

 03/02/2022:
04/02/2022:
 05/02/2022:
 

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