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Feb 3 • 6 tweets • 4 min read
All eyes on Westport (again). #ExtremeWeather #nz

An overnight satellite + weather radar overlap (12 hours) showing consistent moderate rain in the Buller River catchment.

The next 36 hours will be critical. With evacuation of the town expected today.
A live video cross to @radionz's @CheckpointRNZ from Westport, reporting on preparations in the town which was severely flooded last July by a similar #extremeweather event. rnz.co.nz/national/progr…
Here's a broader view showing all of NZ and the cause of the rain converging atmospheric rivers coming together over the Tasman Sea and bringing a continuous stream of thunderstorms towards the Southern Alps.
High resolution satellite pictures of this taken yesterday morning.
Thread on the this #ExtremeWeather event which is expected to have a significant impact in terms of extreme rain and flooding over NZ's South and North island over the coming five days.
And beyond five days there is more #ExtremeWeather in the forecast. This thread looks at the long-range weather model forecasts, and the causes of this #KiwiDeluge.

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More from @althecat

Alastair Thompson Profile picture
Feb 5
NZ's #ExtremeWeather event is not over.

Simulations of the area of tropical moisture that brought torrential rains to the South Island now show a storm system moving south into the Tasman Sea resulting in intense rainfall across Northern NZ through Feb 12th.
Forecasts for this system's exact impact remain highly uncertain but four major global forecasting models are in agreement that some form of extreme weather for NZ will be result.

These are the latest ensemble tropical storm "spaghetti" track graphics for storms north of NZ. ImageImage
The event is expected to begin within 24 hours these are four different models showing the intense area of atmospheric moisture moving over Northern NZ this morning (Sunday) NZT. ImageImageImageImage
Read 20 tweets
Alastair Thompson Profile picture
Feb 5
#Batsirai #ExtremeWeather Update Thread:

Cyclone Batsirai is weakening and accelerating on its final approach to Madagascar's East Coast. But while lower winds will be helpful - it's primary impact - widespread very heavy rain - is likely to be extreme.

The official forecast has not been updated, the eyewall landfall (diminished by the filling of the eye) is likely to take place a little later than forecast but wind and rain is already building over the island as is obvious in the satellite imagery. Image
As of 20 minutes ago the center of the cyclone had roughly 100kms to travel to the shoreline. It will a bring a significant tidal surge with it, especially on the southern side and likely cause significant coastal flooding over a large area of the coastline. ImageImage
Read 13 tweets
Alastair Thompson Profile picture
Feb 4
#ExtremeWeather Split screen.

Two world's apart.

The US Eastern Seaboard and Madagascar.

The US experiencing yet another of what it calls "bomb cyclone". Madagascar about to experience a cyclone which will be much more like a bomb. ImageImage
Both #Extrremeweather events caused by climate change, and 30+ years of failure to address known extreme damage to the biosphere caused by avoidable harms.

One nation responsible for the peril.

Another defenceless against it's catastrophic harms.
In one nation the harms will be felt mostly in travel delays.

In the other nation many will likely die, and 100s of thousands will have their lives scared and livelihoods threatened, and will likely be dependent on humanitarian aid for months if not years.
Read 4 tweets
Alastair Thompson Profile picture
Feb 4
#Batsirai #ExtremeWeather Update Thread.

As a poster child for the impact of climate change on developing nations this cyclone, is a truly terrifying phenomena. In the next 24 hours it will make landfall at most likely Cat 4 or Cat 5 Hurricane Strength.

The animation above is live and covers the last three hours. This animation shows the last 24 hours.

Madagascar is an impoverished nation of nearly 30 million people the majority of whom live in the path of this Cyclone's wind and forecast extreme rain.
Whilst at Cat 4 strength a day ago what was already Intense Cyclone #Batsirai underwent a eyewall replacement and slowed down, it is now accelerating and strengthening. Image
Read 10 tweets
Alastair Thompson Profile picture
Feb 3
#NZ #ExtremeWeather Update Thread.

The quoted thread addresses the long term threat posed by current conditions - beyond five days - around which there is a lot of uncertainty.

Here's the latest ECMWF model PWAT forecast for the current event - next three days.
The longer term picture depends on a complex storm picture north of NZ with a potential 2nd #ExtremeWeather event beginning around 9th Feb.

The current atmospheric river generated event is expected to conclude in around 5 days. Here's the latest GFS 5 day rain accumulation sim.
Beyond five days as detailed in the quoted thread, the global weather simulations diverge. Here is the GFS's current simulation rainfall expectations Feb 8-13. In this scenario the bad weather continues for a further 6 days.
Read 7 tweets
Alastair Thompson Profile picture
Feb 3
This is the UK-Met model's solution at 120 hours. As the AccessG model is associated with the UK-Met model (which only runs for 144 hours) for this reason I am discounting it in this scenario. The ECMWF and GFS models are the two tropical phenomena specialist models.
Here we see the ECMWF models 120-240 hour prognostication.
And here's the GFS 120-240 hour prognostication.

The main difference at the starting point is that the GFS is expecting four lows two strong & two weak and this results in a sharply different outcome.
Read 9 tweets

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